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DETAILED ANATOMY NOTES - Editorial Comment

Editorial Comment (Editorial Overview Text Replicated on Overall Species page - Loxodonta africana - African Elephant
  • Elephants show a number of adaptations for their large size. 
  • Elephants have a large brain with a highly convoluted temporal lobe which may be important for storage of social information and information about good feeding areas, dangerous places etc. The olfactory lobe is also large.
  • The digestive system is broadly similar to that of the horse, with a simple, relatively small stomach but a large colon and a very large caecum. There is no gall bladder.
  • The respiratory system is notable for the lack of a pleural space; the lungs are attached to the chest wall and diaphragm by connective tissue.
  • The vomeronasal organ is large and connects only to the oral cavity, not to the nasal cavity.
  • The heart has a double apex and paired anterior vena cavae. The ductus arteriosus connects between the left pulmonary artery and the aortic arch, as in humans, rather than from the pulmonary trunk to the aortic arch as in other mammals.
  • The kidneys are retroperitoneal and multi-lobed. The bladder has a capacity of six to 18 litres. In females, the urethra and the vagina both open into the long urogenital canal which opens at the vulva between the hind legs. In males, the urethra extends to the end of the penis. There is no os penis. There is no scrotum, the testes remaining intra-abdominal. There are three types of accessory glands: seminal vesicles, prostate and bulbourethral glands. The uterine horns are joined externally for much of their length but remain separate internally until close to the vagina. The placenta is zonary and non-deciduate. Placental scars remain permanently visible in the uterus. The clitoris is well developed and has a large, erectile corpus cavernosum.
  • The skeleton is well adapted for the size of the animal. The cervical vertebrae are short. The appendicular skeleton forms solid columns, with the glenoid fossa in the scapula and the acetabulum in the pelvis facing downwards, long femur and humerus, both radius and ulna fully present in the forelimb and fibula as well as tibia in the hind limb.

Further information is available within this section on the structure of the brain, respiratory system, vomeronasal organ, cardiovascular system, gastro-intestinal system, liver, spleen, urogenital system (including details of the reproductive systems of adult males and females), skeleton, skin and endocrine glands. 

(References are available in detailed literature reports below)

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Detailed Anatomy Notes

Source Information In General:

Elephants show a number of adaptations for their large size. 

Brain:

  • Elephants have a large brain, weighing in females 3.6 to 4.3 kg (8.0 - 9.5 lb) and in males 4.2 to 5.4 kg (9.3 - 12.0 lb). (B285.w3)
  • The temporal lobe is highly convoluted; this may be related to storage of information regarding identities and behaviour of other elephants as well as good feeding areas, droughts, dangerous places etc. (B285.w3)
  • The brain is large, up to 6.5 litres in volume, and weighing up to 6.0 kg (for a large African bull). (B384.4.w4)
  • The cerebral cortex is large, as is the neopallium (responsible for memory). (B384.4.w4)
  • The brain is 4.2 - 5.4 kg (9.25 - 12.0 lb) in the adult male and 3.6 - 4.3 kg (8.0 - 9.5 lb) in the female. Its dimensions are about 35 cm long, 30 cm wide and 20 cm deep and its volume is about 6,600 cc. (B453.5.w5)
  • The cerebrum is highly convoluted. The temporal lobe shows considerable development, projecting anteriorly and ventrally, the frontal lobe is large while the olfactory lobe is enlarged and somewhat flattened, being connected to the cerebral hemisphere by a hollow stalk, separated by a deep fossa from the frontal lobe. (B453.5.w5) The occipital lobe is indistinct and the cerebellum is uncovered, with the parietal region passing smoothly to the temporal lobe. The corpus callosum is large and medially for much of its length is closely applied to the body of the fornix. In the cerebellum, lobule I is strongly developed, lobule II is reduced, lobule III is wider than lobule IV. The pons is quite broad; the medulla oblongata is unremarkable. The pituitary is pear shaped, lying in the hypophyseal fossa of the sphenoid bone. While the pituitary increases in size from 0.7 g in calves of less than six months old to 7.2 g in elderly elephants, its size as a proportion of total body size actually decreases. (B453.5.w5)
  • The brain is situated at back of the skull. It is quite large and grows considerably after birth, the calf's brain being only 35% of the size of the adult's brain. The cerebrum is highly convoluted, although not large enough to cover the cerebellum. The temporal lobe increases in size most during development. (B451.1.w1)
  • Elephants have a large brain, averaging 4,783 g in the adult (range 4,000 - 6,075 g, excluding three reported as 6,500, 7,455 and 9,000 g) and 50% of this in the newborn calf. The cerebellum is very large, averaging 18.6% of the total brain weight, and is visible dorsally. There are well developed cerebral frontal, parietal, temporal, limbic and insular lobes; the occipital lobe is relatively small. The olfactory bulb is large and the olfactory tract foreshortened in comparison to this. Despite the complex sulcal pattern, the sulci are shallow and there are relatively few "buried gyri". The cortical thickness is fairly uniform, minimum 2.3 mm, maximum 4.1 mm. The cranial nerves follow a similar pattern to that in man; the greatest difference is the nerves to the proboscis; the maxillary division of the trigeminal (V) sensory nerve and the facial (VII) motor nerve come together anterior to the eye , forming the great proboscideal nerve. The pituitary gland is large, pear shaped, with a narrow infundibular proximal part, hollowed inside by the recess of the third ventricle. In one Asian elephant it measured 32 mm long, 2.2mm at its widest and weighed 6.16 g. The pineal gland is indistinct, and weighed 0.08 g in one elephant; in another it could not be identified. The dura mater is 10 mm thick (compared with 3 mm in humans) with four folds: the falx cerebri between the cerebral hemispheres, tentorium cerebelli between the cerebellum and cerebrum, falx cerebelli between the lateral lobes of the cerebellum and the diaphragma sellae "covering the roof of the sella turnica with the pituitary body inside, leaving a small opening for the pituitary stalk". The arachnoid membrane, subarachnoid space and pia mater are unremarkable, similar to those of humans. Two pairs of arteries supply the brain: the internal carotid and the vertebral arteries; the joining of these arteries and their branches forms the arterial circle at the base of the brain. The superior sagittal sinus, inferior sagittal sinus and straight sinus, collecting blood from the cerebral veins and returning it to the internal jugular, are identifiable. (J397.70.w1)

Respiratory system:

  • There is no pleural space; the lungs are attached to the chest wall by fibrous connective tissue. (B10.49.w21, B384.3.w3)
  • The lungs are bilobed. (B384.3.w3)
  • Elephants breath by diaphragmatic movement rather than movement of the ribcage. (B384.3.w3)
  • The large circular external nares are located at the extremity of the trunk and are separated by a thick, fleshy septum. The nasal passages are lines with moist epithelium. At the trunk base the nasal passage enters the bony nasal fosae; the bony nares then lead ventrally and posteriorly into narrow bony passages with a vascular muco-periosteum lining. The passages are separated by the mesethmoidal cartilage then by the vomer. Dorsally these is a connection to the olfactory areas of the nasal fossa. The posterior nares are transversely narrow and for a dorsally pointed arch. (B453.3.w3)
  • Elephants have a large larynx. (B453.3.w3)
  • The epiglottis is short and thick. (B453.3.w3)
  • Elephants have strongly marked vocal cords about 7.5 cm (3.0 inches) long, lying in a pharyngeal groove, as well as reduced "false" upper vocal cords. (B453.3.w3)
  • The trachea, about 30 cm long and five to seven centimetres in diameter, is supported by stout, dorsally incomplete, cartilaginous rings. There are about six cartilaginous rings on each of the two bronchi before they enter the lungs. (B453.3.w3)
  • The lungs are large and are attached by tough connective tissue to the chest wall and the diaphragm, without any pleural cavity. (B453.3.w3)
  • The edges of the lungs are rounded and the lobules are not easily seen macroscopically. It is sometimes possible to distinguish an infracardiac or secondary lobe on the right, slightly larger lung. (B453.3.w3)
  • The lungs are directly adherent to the chest wall, with no pleural cavity. (B451.1.w1)
  • The internal nares are high on the forehead. (B451.1.w1)
  • The left lung has one lobe while the right lung has two or three lobes. (B450.15.w15)
  • The lungs are connected to the thoracic wall by extensive fibrous tissue. This suggests that diaphragmatic rather than costal movements are important for respiration. The diaphragm extends as far cranially as the second or third rib. (B450.15.w15)

Vomeronasal organ

  • The opening to the vomeronasal organ is visible on the hard palate, just behind the base of the trunk. (P80.1.w1)
  • The vomeronasal organ (VNO) of the African elephant is large and well developed. The VNOs open into the oral cavity, and not into the nasal cavity. This occurs via the large palatal parts of the nasopalatine ducts, which are lined with stratified squamous epithelium and originate from an anterior recess of the mucosa of the oral cavity. The neuroepithelium of the VNO has a dorsomedial position and is thicker than the receptor-free lateral epithelium. (J393.85.w1)

Cardiovascular system:

  • Superficial veins are observable only on the ear (both interior and exterior surfaces), the anterior surface of the proximal forelimb and the medial aspect of the distal part of the hindlimb. (B10.49.w21)
  • In "all sheltered areas of the body, including superficial and deep temporal, pharyngeal, pectoral, anterior and internal femoral, popliteal, axillary and brachial regions" there are large venous plexuses and free anastomoses. (B10.49.w21)
  • The heart is about 5% of the elephant's body weight. (B384.4.w4, P80.1.w1)
  • The heart is about 50 x 50 x 50 cm in an adult. and weighs up to 27.5 kg. The apex is bifurcated; this feature is more prominent in debilitated, elderly and captive elephants. (P80.1.w1)
  • The amount of fat surrounding the heart indicates the elephant's general health and body condition; in the healthy elephant it is light in colour, firm and abundant. (P80.1.w1)
  • There are paired anterior vena cavae. (B384.4.w4, P80.1.w1)
  • The extremity of the heart is bilobed. (B384.4.w4)
  • The heart has a bifurcated apex, clearly distinguishable in the fetus and young calves, as well as in e.g. elderly, debilitated or captive elephants, although this may be scarcely detectable in the heart of a healthy wild adult elephant. (B453.4.w4)
  • There are paired anterior vena cavae. (B453.4.w4)
  • Elephants show some individual variation in the shape and proportions of the heart, prominence of the bifurcated apex, degree of myocardial tone and arrangements of the brachiocephalic arteries and the coronary arteries. (B453.4.w4)
  • The heart is about 0.5% of total body weight. The ventricles are slightly separated at the apex. There are paired vena cavae. (B451.1.w1)
  • The heart has a bifurcated apex and paired anterior vena cavae. (B450.14.w14)
  • The ductus arteriosus connects between the left pulmonary artery and the aortic arch, as in humans, rather than from the pulmonary trunk to the aortic arch as in other mammals. (B450.14.w14)
  • There is variable anatomy of the vessels at the origin of the brachiocephalic trunk from the aortic arch as indicated by different dissections: there may be two branches from the aorta, a left subclavian and the brachiocephalic, this then dividing to give the right subclavian and the two carotid arteries, or three branches from the aorta, consisting of right and left subclavian arteries and a common trunk dividing to give the two carotid arteries. (B450.14.w14)
  • The posterior vena cava has a ventral wall much thicker than its dorsal wall; this may provide protection against collapse due to suddenly high intra-abdominal pressure (extra support is not required for the dorsal wall which is protected by the vertebral column). (B450.14.w14)

Gastro-intestinal system:

  • The tongue is short. (B384.3.w3)
  • A narrow, sphincter-like slit connects the mouth to the throat. (B384.3.w3)
  • There is a distensible pharyngeal pouch separated from the oesophagus by a sphincter, lying superior to the larynx; the elephant uses this to control the flow of food/fluid into the oesophagus. (B10.49.w21)
  • The stomach is simple. The digestive system is generally similar to that of horses. (B10.49.w21)
  • Necropsy measurements have shown that the small intestines are about 2.1 m long, the large intestine 12.8 m long and the caecum 0.6 to 1.5 m long. (B10.49.w21)
  • At necropsy, stones and soil may be found in the stomach. These are presumably consumed incidentally with plants and salts. (B453.2.w2)
  • The relatively short oesophagus has a narrow lumen; individual items of food rarely exceed 5 cm in the longer axis. Its wall contains abundant mucous glands. (B453.2.w2)
  • From a sample of 14 elephants in East Africa, the average maximum particle length in the stomach was found to be 0.53 cm. (B453.2.w2)
  • The oesophagus is attached to the trachea by fibrous connective tissue and muscle. (B453.2.w2)
  • The stomach is simple, with an average adult length of .0 - 1.4 m and a diameter of 0.4 m. The main axis is nearly vertical. On the diaphragmatic aspect is fund the cardiac orifice; there is a clear demarcation between the oesophagus and the cardia. There is a conical fundus, about half way along the anterior border, with folded mucosa; folds decrease in size towards the base of the fundus, to merge with the smooth mucosa of the rest of the stomach. The middle of the lining of the lesser curvature of the stomach, about 0.11 - 0.12 m beyond the cardia, is glandular. The body of the stomach narrows towards the pylorus but there is no distinct pyloric valve. The total weight of the empty stomach may reach 36-45 kg (80 - 100 lb) in a large bull. (B453.2.w2)
  • The small intestines are about 11 m long, including a U-shaped duodenum and a coiled jejuno-ileum on a fan-shaped mesentery bearing the large mesenteric veins and arteries. The small intestine may reach a diameter of about 13 - 20 cm (5-8 inches). The bile duct and pancreatic duct open onto the duodenum on a single papilla about 10-15 cm ( 4 - 6 inches) from the pylorus, usually with a common opening but sometimes separately. The ileum joins the caecum at the ileo-caecal valve. Peyer's patches in the ileum are largest near the ileo-caecal valve. (B453.2.w2)
  • The large intestine is about 6 m in length. The diameter of the caecum may reach 1.8 m (6ft). (B453.2.w2)
  • The pancreas, in the duodenal loop, is highly lobular, about 50 cm (20 inches) long and may weigh 1.5 - 2.0 kg (3.25 - 4.5 lb); there is a single large pancreatic duct. The pancreas contains Islets of Langerhans, as in other species. (B453.2.w2)
  • The colon and rectum, suspended on the mesocolon, are large, with no clear demarcation between the colon and rectum. Their mucosa is smooth with shallow folds. The rectal canal, about 35 cm (14 inches) long, containing formed faeces, terminates in the anal sphincter on a raised anal flap. The caecum is very large, up to 1 m (40 inches) long, and sacculated, with a notched, rounded, forward-facing fundus. The left wall of the caecum is connected to the ileum by an avascular mesotyphlon. Large arteries and veins of the caecum are found in folds of mesentry. (B453.2.w2)
  • The mouth is relatively small and does not open very wide. It has well developed salivary glands. (B451.1.w1)
  • The oesophagus is short and has plentiful mucus-secreting glands. (B451.1.w1)
  • The simple stomach is cylindrical in shape and nearly vertical in orientation. It is mainly a storage organ, although there is a central glandular region. (B451.1.w1)
  • The intestines may be up to 19 m long. A large, sacculated caecum is present at the junction between the small and large intestines. The walls of the caecum are highly vascularised and relatively thin. (B451.1.w1)
  • Over the anus is a distinctive skin fold, the anal flap. (B451.1.w1)
  • Elephants have a simple stomach; the cardiac portion mucosa has expansible folds; there is a thick cardiac sphincter. The posterior third has smooth mucosa. (B450.13.w13)
  • There may normally be sand and small pebbles within the gastro-intestinal tract. (B450.13.w13)
  • The liver may be bilobed or trilobed. (B450.13.w13)
  • The stomach is relatively small. (B387.w4)
  • The caecum is very large. (B387.w4)

Liver

  • The liver generally has three lobes although there is some individual variation. The largest lobe is usually the left lateral; the left central and right lobes are smaller. It may weigh 36 - 45 kg (80 - 100 lb) in an adult cow elephant and 59 - 68 kg (130-150 lb) in a bull. Elephants do not have a gall bladder; the main hepatic duct, about 15 cm ( 6 inches) long emerges from the liver in a bundle of connective tissue together with the hepatic portal vein, inferior vena cava and diaphragmatic suspension. (B453.2.w2)
  • The liver, weighing up to 68 kg in a mature bull elephant, usually has three lobes, but there is some individual variation. There is no gall bladder; the main hepatic duct is large. (P80.1.w1)
  • Elephants lack a gall bladder, (B10.49.w21, B384.3.w3) but the bile duct is large and saculated. (B10.49.w21)

Spleen

  • The spleen, on the left antero-lateral stomach, is a long, parallel-sided strap, dark reddish black with a tough whitish grey connective tissue covering. In a large bull it may weigh 9.5 kg (21 lb). (B453.2.w2)
  • The spleen is dark red and covered with a tough, whitish connective tissue capsule. Often there are dark red raised nodules, which are normal (although appearing like subcapsular haemorrhages). "Daughter spleens" may be present, attached to the same ligament from the stomach. (P80.1.w1)

Urogenital system:

  • Elephants have multi-lobed kidneys, with five to seven lobes per kidney. (B10.49.w21)
  • In females, the urethra enters the long urogenital canal just posterior to where the vagina joins the urogenital canal. (B10.49.w21)
  • The kidneys are retroperitoneal and lobulated, with individual variation in lobulation, which appears to decrease through the elephant's life (dividing connective tissue sheets are still present) and are each covered by a capsule of dense connective tissue, plus renal fat, in large amounts in healthy animals. (B453.2.w2, P80.1.w1)
  • The junction between the cortex and the medulla is easily visible in the fresh healthy kidney. (P80.1.w1)
  • The spermatic artery arises from the renal artery in some individuals. (P80.1.w1)
  • There is a distinct demarcation visible between the cortex and medulla. The kidney's hilus forms a deep cavity in the centre of the medial border. (B453.2.w2)
  • The ureter branches into calyces, these opening into bulbous dilatations from which arise the lesser calyces which terminate in bulbular areas from which arise the renal collecting tubules. (B453.2.w2)
  • The short straight ureters pass ventrally from the hilum and obliquely into the urinary bladder via semilunar slits. (B453.2.w2)
  • The urinary bladder is covered with peritoneum and attached by peritoneal folds to the pubis. Internally, the smooth mucous membrane is not greatly folded. The internal diameter may reach 30 cm by 24 cm. (B453.2.w2)
  • The vagina and the urethra open into a long urogenital canal, which opens at the vulva between the hind legs. (B451.1.w1)
  • The kidneys are lobed irregular ovals. The ureters, renal vein and renal artery enter at the hilus. (B450.21.w21)
  • The ureters, round and found in a fold of peritoneum travel caudally from the kidneys to the urinary bladder where they enter the bladder on its dorsal surface, travelling obliquely through its wall to end in semilunal slits on the internal surface. (B450.21.w21)
    • In males the ureters cross the ductus deferens near the bladder. (B450.21.w21)
    • In females the ureters originate opposite the ovaries; they pass on either side of the rectum and uterus on their way to the bladder. (B450.21.w21)
  • The bladder, which is at least partially covered by peritoneum, has a capacity of six to 18 litres. The mucous membrane of the bladder is transitional epithelium. (B450.21.w21)
  • The bladder is relatively small (volume about 4 - 6 L) and pear shaped. There are three layers of smooth muscle. the bladder is well fixed by ligaments. The urethra is about 8 - 11 cm long and 3 - 4 cm diameter. The caudal parts of the ureters about 4 - 6 mm thick, are integrated into the bladder wall. (J54.19.w1)
  • In females, the short urethra terminates in the urogenital canal above the vaginal opening into the canal. The urogenital canal, about 100 cm long, terminates at the vulva. (B450.21.w21)
  • In males, the urethra is long, extending to the glans penis. (B450.21.w21)

Reproductive Male:

  • The testes are retained within the abdominal cavity. (B147, B10.49.w21, J62.38.w2)
  • The testes are intra-abdominal. There is no pampiniform plexus, cremaster muscle or inguinal canal. There is no distinct epididymus. The Wolffian duct is highly convoluted. There are large, thick-walled seminal vesicles, large bulbo-urethral glands full of viscous secretion, and the prostate is found on the dorsal wall of the urethra, just posterior to the seminal vesicles. The penis has no os penis but has a well-developed corpus cavernosum and large, paired levator penis muscles, which produce the S-shaped flexure of the erect penis. (P80.1.w1)
  • The testes are internal, close to the kidneys, nearly round, and can reach 15-23 cm diameter; in the immature elephant it may be 2 cm (in a newborn) to about 9 cm diameter. Elephants have paired bulbourethral glands, caudal to the root of the penis and about 2 cm under the surface of the skin; these are "fist-sized"; by ultrasound they appear mainly solid, with an irregular-shaped central cavity. The root of the penis is about 20 cm diameter and heavily vascularised. The colliculus seminalis is an integral part of the dorsal wall of the urethra, about 1 cm caudal to the urinary bladder, about 1.5 cm long, 8 mm diameter, and contains the joint ducts of the ampullae and paired seminal vesicles as well as at least three individual ducts on each side from the lobes of the prostate. The prostate gland, up to 5 cm in size (each side) is paired, each half consists of three lobes and it is found above the pelvic urethra and caudal to the ampullae, which are cone-shaped, with a maximum diameter of 5 cm. The ampullae are located above the urinary bladder, at the cranial part of the urethra, at the ends of the ductus deferens, collecting sperm directly from the testes (no well-developed epididymes). The seminal vesicles may contain up to 400 ml fluid each and the central cavity of each gland is surrounded by a wall 5-10 mm thick with an internal mucosal layer and an external muscular layer. The ductus deferentes complex, strongly coiled, are up to 2 cm in its widest diameter and about 1 m in length. (J54.19.w6)
  • The intra-abdominal testes may weigh 2 kg each in a breeding bull. During musth, the volume of the testes may be four times the size outside musth. The prostate of African elephants has three clearly distinguishable lobes on each side, with separate internal cavities, and can reach 6 cm diameter.(J23.40.w1)
  • The penis is generally similar in structure to that of horses; "additional tendon and muscle structures aid in voluntary "searching" motions during mating." (B10.49.w21)
  • Elephants possess seminal vesicles, prostate and bulbourethral glands. (B10.49.w21)
  • The testes remain intra-abdominal, found medial and slightly posterior to the kidneys, loosely suspended by a fold of peritoneum by the mesorchium. The testis is smooth, ovoid or spherical with a firm, fibrous tunica albuginea, while the main tissue is divided into lobules, composed of seminiferous tubules, by radiating fibrous septa. There is no distinct epididymis, nor is there a pampiniform plexus or cremaster muscle (nor an inguinal canal). A birth each testis may be about 4.5 by 3.5 cm and weigh about 250g while in the adult bull each may be 17 by 15 cm and weigh 3 kg. (B453.6.w6)
  • Elephants have paired large, oval, thick-walled seminal vesicles in the pelvic cavity, a prostate gland posterior to the seminal vesicles, on the dorsal wall of the urethra, usually bilobed, with one lobe either side of the urethra, but in some individuals multilobed, and paired bulbo-urethral glands on the dorso-lateral urethra near the ischial arch. (B453.6.w6)
  • The urethra in the adult is more than 75 cm long. It has a Y-shaped opening onto the ill-defined urethral process at the apex of the glans penis. There is a pars prostatica adjacent to the prostate, a narrow-lumened pars isthmica and, separated from this by a muscular sphincter, a wider pars cavernosa through the corpus spongiosum of the penis. (B453.6.w6)
  • The penis is long and may weigh more than 27 kg (60 lb) in the adult (including attached skin). The free end of the penis and prepuce may be unpigmented. There is no os penis. (B453.6.w6)
  • The testes remain intra-abdominal, suspended in a fold of peritoneum and connective tissue from the lumbar region of the dorsal body wall. There is no obvious epididymis. Spermatozoa are stored in the Wolffian duct. This contains a mass of coiled tubules, about 1.0 m long and has a diameter initially of 1 mm, increasing to 5.0 mm centrally and more than 1.0 cm distally. It opens into the duct of the seminal vesicle, forming a common ejaculatory duct. (B451.1.w1)
  • The penis does not contain a baculum. Erection involves dilation of blood vessels in erectile tissue, with muscular contraction then giving an S-shaped flexure for penetration of the female's vulva. The end of the penis, and the prepuce enclosing it, are unpigmented. The urethral opening on the tip is Y-shaped. Most of the time the penis is within a dermal sac on the perineal region. (B451.1.w1)
  • The testes are intra-abdominal. (B387.w4)

Reproductive Female:

  • There is a single pair of nipples, just behind the front legs. (B147); between the forelegs. (B285.w3)
  • A urogenital canal, 40 to 100 cm long in an adult cow elephant, separates the vagina from the vulva. (B10.49.w21)
    • The long urogenital canal forms a common passage for the urinary and genital tracts of the female elephant. (B396.3.w3)
  • The urogenital canal (vestibule) is very long (1.0 - 1.4 m) in elephants. This tube-like structure runs vertically upwards from between the hind legs toward the tail before curving forward horizontally to form a 20-40 cm sac above the bony pelvis; the urethra and vagina open into this sac. The glans clitoris, close to the external opening of the urogenital canal, measures about 7-12 cm. The vagina, about 30 by 15 by 10 cm, has many longitudinal folds. Semen is deposited here during mating, and during pregnancy it fills with thick mucus. In nulliparous females there is a hymen-like structure; this is not ruptured by mating. The vaginal os is about 0.4 by 0.2 cm and is flanked by two blind pouches which are relicts of the Wolffian ducts. By one year postpartum, the vaginal os measures about 1.0 by 1.0 cm and the blind pouches are no longer detectable. (J54.19.w1)
  • There is a long urogenital canal, such that the genital opening is anterior to the hind legs. The clitoris is large (up to 50 cm) and found in the ventral vulva beneath the entrance to the urogenital canal. the uterus has a common body and two horns. There is a permanent implantation scar left by each placenta; the placenta is zonary and deeply attached to the uterus. The mammary glands are found between the front legs. (P80.1.w1)
  • The urogenital canal or vestibule of elephants is about 1.3 m long. In nulliparous females there is a hymenal membrane with an opening (os) of only 4 mm x 2mm, on either side of which is a blind pouch of a similar diameter and 60 +/- 28 mm long. (J23.40.w1)
  • During the first half of pregnancy there are many corpora lutea, seven on average (range two to 26 on one ovary). (B384.5.w5)
  • The placenta of elephants is zonary and leaves a thin horizontal scar which may be detectable in the uterus for 30 years. (B384.5.w5)
  • The fetal ovaries hypertrophy in late pregnancy and may be larger than the same ovaries at puberty: a study in East Africa found that the mean weight of the ovaries (both ovaries combined) at full term was 110 g but then declined, followed by growth so that the mean weight was 68 g at first ovulation for females from the Murchison Falls National Park, Uganda, North bank population and 90 g at first ovulation for females from the South bank population. The ovaries grow heavier than their weight at full term only when the female reaches about 24 years of age. (P17.21.w1)
  • The ovaries are situated close to the kidneys and each is nearly fully enclosed by the funnel of the fallopian tube, this forming an ovarial sac attached by a suspensory ligament to the body wall and by an ovarian ligament to the uterine horn. The Fallopian tubes join the uterine horns deep in the muscular and connective tissue of the uterine horns. Externally the uterine horns are fused for much of their length, however internally they are separate for a longer distance before opening into the common uterine body. Implantation scars, which appear to be permanent, are usually found in the region in which the horns are separate. The uterus opens into the vagina, marked only by an annular thickening of the wall. The vagina is much thinner walled than is the uterus. The urogenital canal is very long. The clitoris is large and well developed. (B453.6.w6)
  • The corpora lutea remain rather than regressing following pregnancy. They do not secrete progesterone. (B451.1.w1)
  • The clitoris is well developed and has a large, erectile corpus cavernosum. (B451.1.w1)
  • The well-developed vulva normally faces anteriorly but due to erection of the clitoris, during copulation it is turned ventrally and posteriorly. (B451.1.w1)
  • The elephant's placenta is non-deciduate (no maternal tissue is found in the expelled placenta) and zonary (the villi are arranges in a strap-like manner around the membranes). (B212.w11)
  • In the last days of pregnancy in elephants, large blood vessels are present within the mammary gland (visible using ultrasound); and in the last 24 hours before parturition, large fluid filled irregularly-shaped cavities are present within the mammary glands. (B455.w3)
  • The placenta is zonary and endotheliochorial. The trophoblast erodes the lumenal epithelium of the endometrium and stimulates upgrowths of stromal villi containing blood vessels. (J68.361.w1)

Skeleton:

  • The skeleton makes up 12-15% of the total body mass of the elephant. (B147)
  • The skeleton is about 16.5% of total body mass in elephants. (B384.3.w3)
  • The African elephant has a total of 57 to 67 vertebrae, including 26 to 31 vertebrae in the tail. (B384.3.w3)
  • The seven cervical vertebrae of the elephant are fused flattened discs capable of only limited movement. (B384.3.w3)
  • Typically there are seven cervical vertebrae, 24 thoracolumbar vertebrae (with 20 or 21 bearing ribs), four sacral vertebrae and 28 to 33 caudal vertebrae. (B453.1.w1)
    • The cervical vertebrae are flattened antero-posteriorly and, except for the seventh cervical vertebra, have reduced spinous processes. (B453.1.w1)
    • The thoracic vertebrae are compressed antero-posteriorly. The transverse processes are short. The neural spines are long; those of the withers are long and inclined posteriorly. (B453.1.w1)
    • The ribs are wide and flattened. The five posterior pairs of ribs are not attached to the sternum. (B453.1.w1)
    • The short thick sternum is made up of four sternebrae and has a distinct anterior keel. (B453.1.w1)
    • The lumbar vertebrae have massive, short centra and dorsoventrally flattened transverse processes. (B453.1.w1)
    • There are four sacral vertebrae. (B453.1.w1)
    • The caudal vertebrae are simple and lack any neural spine by the ninth bone, then have only the cylindrical centra. (B453.1.w1)
  • The forelimb has no clavicles but a large flattened triangular scapula, longest anteriorly and shortest on the postero-dorsal border, with the main axis approximately vertical at rest. There is a large scapular spine and the acromium process bears a strongly curved metacromium; the rounded coracoid process is insignificant. The fairly shallow glenoid fossa is directed ventrally. The humerus has a hemispherical articular head; the bone is heavy and sturdy. The deltoid ridge is strongly marked; this and the spinal groove run for the proximal two thirds of the length of the bone. There are greater and lesser tuberosities on the humeral head. The distal third of the shaft bears the lateral suprecondylar ridge, terminating in the shallow trochlear surface on which the ulna articulates. The radius and ulna are separate from one another, permanently in the pronated position with the radius's head locked between the ulnar processes. The ulna is large and heavy, with a convey, sturdy olecranon process. The smaller radius curves closely around the ulna and the distal ends of the two bones have a tough interosseous ligament holding them closely together. In the carpus there are two rows of compact, squarish bones, and distally there are five metacarpals, somewhat longer, and two phalanges for each digit (usually one phalanx for the first digit). The digits radiate somewhat. (B453.1.w1)
  • The pelvis shows a wide expansion of the ilia and, due to a downward curve of the spine from the junction of the thoraco-lumbar and lumbar vertebrae, the main pelvic axis is in nearly the same vertical plane as the hindlimbs. The iliac crest is elongated, curved anteroventrally and is clearly visible in thin individuals. The ischium and pubis are relatively small. The acetabulum faces ventrally. The femur has a prominent greater trochanter (although less high than the femoral head) and only a vestigial lesser trochanter. The joint if fully extended in the elephant standing at rest. The patella is large, prominent and convex. The knee (stifle) may be slightly flexed when the elephant stands resting one foot. The sturdy tibia is relatively short and has a triangular cross-section; proximally its posterior aspect is deeply concave, giving a semi-circular articular surface. The slender fibula is a separate bone. In the foot, the digits are all aligned antero-posteriorly. There are seven tarsal bones: calcaneous, talus, navicular, three cuneiform bones and a cuboid bone, broad and bearing two postaxial metatarsals. Digit one (hallux) has a reduced metatarsal and only a vestigial phalanx, which for each of digits two to five there is a metatarsal and two plalanges. (B453.1.w1)
  • Elephants have short necks, with a massive double spine on the axis. In African elephants the neck is nearly horizontal. (B451.1.w1)
  • Elephants bearing large tusks have robust cervical spines, required as anchors for the neck muscles, to support the tusks' weight. (B451.1.w1)
  • Elephants have robust vertebrae and stout neural spines; these are high particularly in the thoracic region. (B451.1.w1)
  • Elephants have 20 ribs, arising from vertebrae most of the distance down the spinal column; the rib cage is large and barrel-shaped. (B451.1.w1)
  • The limb bones form rigid columns, with the shoulder and pelvis nearly vertical and the glenoid cavity and acetabulum facing ventrally. The humerus and femur are long, approximately equal in length to the lower limb bones. The radius and ulna are crossed in permanent pronation. (B451.1.w1)
  • The limb bones are well developed and filled with spongy bone; they lack a marrow cavity. (B147)
  • The forefeet are semi-digitigrade; the hindfeet are semi-plantigrade. (B285.w3)
  • There is no clavicle. (B384.3.w3)
  • The scapulae are vertical in position and are relatively large. The pelvis is also nearly vertical, rather than, as in other ungulates, parallel to the ground. (B384.3.w3)
  • Most of the marrow cavities of the long bones have been replaced by spongy bone which is strong and relatively light. (B384.3.w3)
  • The radius and ulna are twisted on one another, in a manner similar to that seen when humans pronate the forearm, but in elephants this positioning is permanent. (B384.3.w3)
  • The epiphyses of the elephant remain open for many years. The last epiphyses to fuse in the long bones are those of the radius. This occurs at about 32 years in the female African elephant and at about 40 years in the male. (B384.3.w3)
  • The long bones have thick, dense cortices and generally lack marrow cavities, these being replaced, except for small areas of the femur and tibia, by reticulated cancellous bone. (B453.1.w1)
  • The seven cervical vertebrae have craniocaudally compressed, very short vertebral bodies and short spinous processes; the transverse processes of C1 to C6 have transverse foramens. Cranially to caudally the spinous processes elongate, the transverse processes become larger, the bodies elongate, the articual processes become placed more horizontally and the vertebral foramens change from dome-shaped to triangular. There are 20 or 21 thoracic vertebrae. Each bears cranial and caudal costal articular facets, except on the last three or four there are only cranial costal facets. There are reduced transverse processes bearing articular facets for the tubercles of the ribs. The spinal processes incline caudally and increase in size from T1 to T3 then gradually decrease; the proximal extremities of the spinous processes are enlarged. Cranially to caudally, the vertebral bodies increase in length and decrease in diameter. There are mamillary processes only on the last few thoracic vertebrae. There are three lumbar vertebrae, similar to the last few thoracic vertebrae, but lacking costal articular facets. There are five sacral vertebrae, the neural arches of which are fused with each other and with the wings of the ileum, while their vertebral bodies remain separate, and the thin intervertebral discs tend not to be ossified. The caudal vertebrae number 19 to 21. The first five or six of these have neural arches which fuse dorsally while in the others the vertebral canal and vertebral foramens remain open dorsally. The processes are lost caudally also, so the last vertebrae are composed of only rod-like vertebral bodies. There are 20 or 21 pairs of ribs. The first rib has a greatly expanded body; the last three or four ribs have reduced bodies. The cartilages of the first five or six ribs articulate with the sternum (true ribs), the first 15 or 16 pairs of ribs bear costal cartilages and the last five or six ribs are not attached to the costal arch. The sternum has five sternebrae, in three segments, made up of the first, second to fourth, and fifth sternebrae respectively. A synovial joint is found at the articulation of the first and second sternebrae and connective tissue loosely attaches the small fifth sternebra (which bears a large xiphoid cartilage, directed caudally), while the second to fourth are fused. (J62.63.w1)
  • The skeleton of the thoracic limb forms an upright pillar of bone, with massive scapula, humerus and ulna (which is the main weight-bearing bone of the forearm); the radius is more slender. Relatively small bones make up the carpus and digits. The scapular is an irregular triangle, with a smaller supraspinous fossa and larger infraspinous fossa separated by the prominent scapular spine. The scapular cartilage ossifies early and is separated from the scapula by an epiphyseal line. The glenoid cavity is only slightly concave and is elongated cranio-caudally. The humerus, the longest, heavies bone of the limb, is elongated cranio-caudally. The ulna is large, about five times as heavy as the radius.. The radius articulates proximally with the humerus, distally with the carpal bones and along its length with the ulna: proximally along its caudomedial surface, distally along its lateral border. The carpus is made up of eight bones in two rows: a proximal row of the radial, intermediate, ulnar and accessory carpal bones and the distal row of carpal bones I to IV. There are five metacarpals, with metacarpal I being notably smaller than the others. Digit I consists of only a proximal phalanx, which is tusk shaped, having a round base and narrowing to a point. Digit V has a proximal and middle phalanx. Digits II, III and IV have proximal, middle and distal phalanges, but the small distal phalanges do not articulate with the middle phalanges, from which they are separated by thick connective tissue; they are firmly attached to the corium of their respective nails. (J62.60.w2)
  • The pelvic girdle has as its most striking feature the very large, curved, three-sided wing of the ileum on either side. There is also the ischium, pubis and shaft of the ileum. The femur is the longest bone of the skeleton: that of a 53-year-old female measured 1 m from femoral head to distal extremity while a femur of a mature male (age unknown) measured 1.27 m and the epiphyseal lines were still clearly visible. The prominent head is an almost perfect hemisphere facing proximomedially. The patella is wedge-shaped in adults but more elongated and slender in juveniles. The tibia, on the medial side and articulating with the femur, is stout and about half the length of the femur while the slender fibula, on the lateral side, has a small head proximally and a prominent lateral malleolus distally. The tarsus is made up of seven bones in three rows: the talus and large calcaneus in the first row, the central tarsal bone in the middle row and tarsal bones I to IV in the distal row. There are five metatarsal bones, of which metatarsal I is smallest and metatarsal III is largest. There are only four phalanges, with the first digit being represented only by a single proximal sesamoid bone. A firm, rib-shaped cartilaginous rod is attached to the plantar surface of the first tarsal and metatarsal bones and reaches to the sole, attaching in the plantar quarter, just medial to the midline. Digits II and V have proximal and middle phalanges only while digits III and IV have proximal, middle and distal phalanges articulating with the middle phalanges. There are paired proximal sesamoid bones on the plantar facets of the trochlea of metatarsal II to V, and a single sesamoid bone on the plantar facet of metatarsal I. (J62.61.w3)

Skin:

  • The skin is linked to the underlying subcutaneous tissue by complex columnar pillars rather than by simple papillae. (B453.1.w1)
  • The pattern of the dermo-epidermal junction varies over the body, with for example a stratum granulosum present on the cheeks but absent on the forehead. The dermo-epidermal junction is characterised by large complex papillae, the surface of these being formed by smaller papillae. (B453.1.w1)
  • Histologically, the dermis consists of a stratum germinativum, stratum spinosum and stratum corneum. (B453.1.w1)
  • Hair follicles are found to open within the inter-columnar grooves and fissures of the skin. (B453.1.w1)

Thymus:

  • The bilobed thymus is found at the base of the neck, on the ventral trachea and antero-ventral pericardium, only in very young elephants as it atrophies very early. (B453.4.w4)

Thyroid:

  • The large, bilobed thyroid, found ventral to the anterior end of the trachea, may weigh 200 - 340 g in the adult African elephant. There are two main lobes, within a single capsule. The parenchyma is grooved into numerous small lobules. (B453.5.w5)

Parathyroids:

  • The two pairs of parathyroids are found on the ventral edge of the thyroid. Each parathyroid is about 5 mm diameter. They are highly vascularised and lobulated. (B453.5.w5)

Adrenals:

  • The adrenals are long, narrow and strap-like or band-like with a lateral horn. In the adult each weighs about 90 - 280 g. Externally they appear smooth and yellowish, with a flabby, fatty texture. In cross section they have a yellowish cortex and greyish-yellow medulla. (B453.5.w5, P80.1.w1)
  • The adrenals are on the dorsal abdominal wall, slightly anterior and medial to the kidneys. They are elongated and flattened dorsoventrally with a broad posterior and pointed anterior end and a stout thumb-like extension on the medial surface, particularly on the right adrenal, which also is larger than the left adrenal. (J332.50.w1)

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Authors & Referees

Authors Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Susan K. Mikota DVM (V.w72)

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