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DETAILED ANATOMY NOTES - Editorial Comment

Editorial Comment (Editorial Overview Text Replicated on Overall Species page - Erinaceus europaeus - West European Hedgehog)
  • Hedgehog anatomy and structure is basic, resembling primitive mammals, apart from specialisation of their integument.
  • Both sexes have five pairs of nipples. In males the prepuce is some distance from the anus, near the navel, while in females the vulva is much closer to the anus. The testes are intra-abdominal.

    Further information is available within this section on the structure of the brain, male and female reproductive organs, gastrointestinal organs and adrenals.

(References are available in detailed literature reports below)

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Detailed Anatomy Notes

Source Information In General:

Hedgehog anatomy and structure is basic, resembling primitive mammals, apart from specialisation of their integument.(B262.2.w2)

Brain:

  • The anatomy of the hedgehog brain is simple based on a "primitive plan".(B258.w2)
  • The olfactory bulbs of the hedgehog are large, reflecting the importance of its sense of smell.(B258.w2)
  • The cerebral hemispheres of the hedgehog are smooth and unelaborated.(B228.2.w2)

Reproductive Male (Boar):

  • Hedgehogs can be easily sexed by examination of the external genitalia.(B262.2.w2, B291.12.w12); the distance between the anus and the genital organ is much greater in the male than in the female: about two inches (5 cm) and 1/2 an inch (1.25 cm) respectively. (B255.2.w2)
  • In the adult male, or boar, the prominent penis sheath (prepuce) is positioned in the midline close to the navel.(B262.2.w2, B260.1.w1, B228.2.w2, B254.14.w14); about five centimetres (two inches) cranial to the anus.(B254.14.w14)
  • Identification of the sex of new-born hedgehogs can be challenging.(B228.2.w2) The prepuce of the male is positioned close to the anus in the infant and gradually migrates forward towards the navel as the animal grows.(B228.2.w2)
  • Care should be taken not to confuse the umbilicus of the neonatal hedgehog with the prepuce of the infant male.(B228.2.w2)
  • The testes are positioned ventrally within the abdomen, close to the body wall and do not descend into a scrotum.(J206.81.w1, B228.2.w2, B142)
  • During the rut, or period of peak male sexual activity, the testes are detectable within a "perineal pouch in the body wall".(B228.8.w8)
  • Testes temperature is maintained at 1.2-1.6C below body temperature during January to March (the season of gonadal activity) but is more variable in late autumn/early winter (October to December) when spermatogenesis has virtually ceased and up to 1C higher than body temperature during hibernation. At body temperatures up to 36.2C the testicular temperature is maintained at 34.0-34.9C; this is thought to be the optimum range for spermatazoa production and maturation in this species. (J206.81.w1)
  • Hedgehogs have a layer of insulating and poorly vascularised fat which surrounds each testicle (B228.8.w8); blood is supplied via a pampiniform plexus (J206.81.w1) and hedgehogs are thought to employ a countercurrent heat exchange system for testicular cooling, as in other species.(B228.8.w8)
  • The hedgehog penis is musculo-cavernous in design. Erection is achieved through engorgement of the corpus cavernosum and via muscular action.(B228.8.w8)
  • The morphology of the glans penis is distinct in (Erinaceus - (Genus)) as compared to other hedgehog genera. Only small keratinous papillae are present on its dorsal surface and lateral extensions are absent.(B228.1.w1, B228.8.w8)
  • The hedgehog penis does not show seasonal variation in size but increases with body size and age.(B228.8.w8)
  • The reproductive system of the boar undergoes tremendous seasonal variation in weight and is large in proportion to relative body size.(B228.8.w8)
    • The reproductive organs may account for approaching 10% of the total weight of the male hedgehog in the reproductive season. (J68.223.w2)
  • The accessory sex glands are well developed in the boar and include large multi-lobed paired seminal vesicles, prostate glands and Cowper's glands.(J68.223.w2)
    • Not all authors agree with the identity of the third set of glands as being Cowper's glands. (B228.8.w8)
  • The accessory glands increase in weight approximately ten fold at the beginning of the breeding season. The seminal vesicles may reach 20-30 g, the prostate glands 9 g and the Cowper's glands up to 9 g; the accessory glands remain well-developed until August but then regress rapidly. (J68.223.w2). The combined mass of these glands has been shown to be up to at least 92 g (8.4% body weight, n=1) (B228.8.w8). It is thought that the relative proportion of body weight contributed by the accessory sex glands is the greatest of all mammalian species.(J68.223.w2, B228.8.w8, B260.6.w6)
  • The weight/size of the testes and epididymis vary seasonally, rising in April and remaining high until the end of August.(J68.223.w2)
  • The accessory glands produce copious volumes of gelatinous material within the ejaculate (J68.223.w2, B228.8.w8). Discussion exists as to whether hedgehogs form a post-ejaculatory sperm plug from the accessory gland fraction, as in other species, which acts to reduce the potential for female conception from a subsequent male through mechanical obstruction of the passage of further deposits of sperm. (B228.8.w8) Investigation of the contents of the upper vagina in one detailed study suggested that gelatinous material present was derived from vaginal and cervical glands and sloughed epithelial cells from the sow's reproductive tract.(J68.223.w1)
  • Both sexes of hedgehog have five pairs of nipples. (B142, B258.w2)

Reproductive Female (Sow):

  • Hedgehogs can be easily sexed by examination of the external genitalia.(B262.2.w2, B291.12.w12); the distance between the anus and the genital organ is much greater in the male than in the female: about two inches (5 cm) and 1/2 an inch (1.25 cm) respectively. (B255.2.w2)
  • In the adult female, or sow, the anus and vagina are positioned close together (approximately 1 cm apart).(B262.2.w2, B228.2.w2, B254.14.w14)
  • There are five pairs of mammary glands, four abdominal and one thoracic, in a ventro-lateral position on the body. (J68.223.w1).
    • The nipples are small in immature females but larger in parous animals.
    • Development of the mammary glands occurs in pregnant and lactating sows where strips of mammary tissue can be palpated, extending from the axillae (armpit) to the inguinal areas (groin).(B228.2.w2, B228.8.w8)
    • Four / five mammary glands in the hedgehog. (B285.w1)
  • The ovaries are fibrous, irregular, bursate (enclosed by a tough peritoneal capsule) and U-shaped. (J68.223.w1).
  • The fallopian tubes, bent round to lie against the tips of the uterine cornu, are about 50-80 mm long. The uterine horns are each about 15-20 mm long and 5 mm in diameter; they are thick and muscular and they meet across the top of the cervix, forming a "T" with the cervix and vagina. (J68.223.w1)
  • The single cervix and vaginal lumen remains patent throughout the year, although with seasonal changes in the size of the large muscular vagina. (J68.223.w1)
  • The clitoris, sometimes containing a small cartilage, projects into the urogenital passage with the epithelial folds of the clitoris merging with those of the vagina. (J68.223.w1)
  • The size and weight of the female reproductive tract increases with age and varies with reproductive activity.(J68.223.w1, B228.8.w8)
  • The sow has a number of cervical and vaginal glands which produce mucous secretions. A pair of small glands are found under the epithelium in the upper vagina, level with the base of the bladder. Larger paired glands are found in the mid-vagina, dorso-laterally on either side of the urethra; similar glands, but smaller, are found near the clitoris. Large fan-shapped glands, probably homologous with Cowper's glands in the male, lie outside the muscular wall, against the pelvic girdle. The glands regress during anoestrus. (J68.223.w1)
  • The chorioallantoic placenta of the hedgehog is typical of that for the Insectivora - Insectivores (Order); it is discoidal and haemochorial.(B228.8.w8)

Gastro-intestinal system:

  • The hedgehog has a simple stomach; the ileo-colic junction is poorly defined, the colon is smooth and non-complex and there is no caecum.(B228.3.w3)
  • When compared with other species within the Insectivora, hedgehogs have stronger jaws, blunter teeth and a longer gastro-intestinal tract.(B228.3.w3, B255.3.w3)
  • The ratio of body length to gut length in the hedgehog is reported to be 1:6 - 1:7 (compared with 1:4 in the stoat (Mustela erminea - Stoat) and 1:10 in the European rabbit (Oryctolagus cuniculus - European rabbit) representing a carnivorous and herbivorous species respectively).(B228.3.w3)

Adrenals

On the basis of information from a limited number of animals, it appears that the adrenals vary in size with season, being larger in the summer than in the winter (J9.182.w1):

Season Number of hedgehogs Body weight (g) Absolute adrenal weight (mg) Relative adrenal weight (mg/100 g body weight)
Early summer  5 560 389 69.5
Midsummer  6 650 305 46.9
Autumn  4 458 253 55.2
Early winter  2 378 231 61.1
Midwinter 9 498 239 48.0
Early spring  3 385 218 56.6
Spring  2 645 267 41.4

 

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Authors & Referees

Authors Becki Lawson (V.w26); Debra Bourne (V.w5)
Referee Suzanne I. Boardman (V.w6); Nigel Reeve (V.w57)

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