Living OrganismsAnimalia / Craniata / Mammalia / Carnivora / Ursidae / Ursus / Species:

< > APPEARANCE/ MORPHOLOGY: DETAILED ANATOMY NOTES with literature reports for the Polar bear - Ursus maritimus: Use sub-contents list below, or simply scroll down the page to view findings.

Click here for full-page view with caption Click here for full page view with caption


Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus maritimus - Polar bear
  • Bears do not have any major anatomical specialisations. The large size of polar bears reduces loss of body heat.

Further information is available within this section on the male and female reproductive organs, gastrointestinal system, urinary system, hepatic system and adipose tissue. 

(References are available in detailed literature reports below)

To Top of Page
Go to general Polar bear page

Detailed Anatomy Notes

Source Information

In General:
  • Bears do not have any major anatomical specialisations.
  • The large size reduces loss of body heat. (B180.w4)


  • Powerful; the muscles of the neck and the hind limbs are particularly well developed. (D244)

Reproductive Male:

  • Wild polar bears captured in the Canadian arctic showed seasonal variation in testis size. In May, testes were measured as 39.4 +/- 3.5 cm², whereas in October testis size was 27.3 +/- 2.0 cm². (J367.123.w1)
  • Bears have small glandular ampullae at the distal ends of the vasa deferentia. (B399.3.w3)
  • Bears have a small prostate gland. (B399.3.w3)

Reproductive Female:

  • Four functional mammae. (B147)
  • Females have four functional teats, the anterior pair slightly posterior to the axillae and about 4 cm from the midline on either side, the other pair about 15 cm further posterior. (D244)
  • The milk is intermediate in fat content between that of whales and seals.
  • Females have two pairs of teats. (B399.8.w8)
  • There are four functional mammae, two just behind the front legs, about 4 cm (1.5 inches) to either side of the midline, the second pair about 15 cm (6 inches) further posterior. (B406.37.w37)
  • Normally there are four functional mammae. Females have been found with five functional mammae, the extra gland in each case being found posterior to the normal glands, about 4 cm from the midline on the anterior abdomen and lactating normally. Another female had two extra nipples, about 15 cm anterior to the vaginal orifice, in the inguinal region, but these were not functional (no milk expressed, while the normal glands were lactating) and in another female the right posterior mammary gland had two nipples, about 3 cm apart from one another, both functional. (J332.71.w2)
  • Female bears have an os clitoris. (J332.69.w1)

Gastro-intestinal system:

  • Typical carnivore gut; the stomach is large; in the adult it may hold more than 70 kg of food. (D244)
  • Bears have a much more heavily muscled pylorus (stomach exit) than other mammals. (P85.1.w4)
  • Bears lack a caecum. (B399.3.w3)
  • Bears have a simple stomach, no caecum, and lack an obvious external differentiation between the small and large intestines. (D251.2.w2)
  • The bears have a simple stomach and a short intestinal tract. The junction between the small intestine and large intestine is marked by a sudden change in mucosa; there is no caecum. (B491)


  • The kidneys of bears are lobulated; the polar bear's kidneys have 65 lobules, more than in any other carnivore. (B399.3.w3)


  • The liver can very high levels of vitamin A. (B490.27.w27)
  • The liver has a vitamin A content of 15,000 - 30,000 units per gram and a very high fatty acid content, but relatively low levels of phosphate, lipid and cholesterol. (D244)


  • The subcutaneous fat layer may be 5 - 10 cm thick. It is particularly thick in adult females before denning. (D244)
  • Female polar bears may have body fat totalling 45% of body weight. (P17.57.w1)
  • Examination of 12 polar bears revealed a blubber layer up to 4 cm thick under a pair of muscle sheets, 2 mm thick, found on either side of the torso 0.5-3.0 mm under the skin. The muscle sheets appeared to be based on latissimus dorsi. The sheets of muscle were well supplied with blood, with "pairs of arteries and veins running from the deep body musculature through the intramuscular blubber layer and out perpendicular to the latissimus sheets." At 3-5 cm intervals large (2-4 mm diameter) veins ran from the dorsal edge of the muscle sheets into the body core. In the limbs, the main blood vessels ran parallel to one another from the elbow or knee to the wrist or ankle (two bears). Over the rump there was a blubber pad up to 11 mm thick. (J460.37.w1)
  • Examination of two elderly (male about 25 years old, female 33 years old) zoo-kept bears revealed 18.7% and 17.5 % of their body masses to be dissectible adipose tissue, within the range of values recorded for adult and subadult wild polar bears in November (after fasting during the summer). Their superficial and intramuscular deposits of fat were not dissimilar from those of wild bears, with similar anterior versus posterior and ventral versus dorsal distribution, but they had substantially more adipose tissue intra-abdominally than did wild bears of similar mass, and in particular more deposition in the inner ventral abdominal wall, with a substantially greater number of adipocytes present than expected. Fatty acid composition reflected the diet and therefore differed from that of wild bears. The male, who had arrived at the zoo from a circus in very poor condition, had relatively few, but large, adipocytes, particularly in peripheral adipose tissue, suggesting compensation for a low adipose count by hypertrophy of the available cells. (J54.12.w2)
  • During a study of Arctic species, vitamin D3 levels in blubber of polar bears was found to be 406.17 +/- 139 (mean +/- SD), range 31 - 873, for six bears. The levels were higher than in mammal species which fed primarily on invertebrates, but not higher than other mammals which fed mainly on vertebrates (fish or other mammals). (J54.23.w3)

To Top of Page
Go to general Polar bear page

Authors & Referees

Authors Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Andrew Derocher (V.w100)

To Top of Page
Go to general Polar bear page