Ý ß APPEARANCE/ MORPHOLOGY: DETAILED ANATOMY NOTES with literature reports for the Sun bear - Helarctos malayanus: Use sub-contents list below, or simply scroll down the page to view findings.

DETAILED ANATOMY NOTES - Editorial Comment

Editorial Comment

• Bears do not have any major anatomical specialisations.

Further information is available within this section on the brain, male and female reproductive organs, gastrointestinal system, urinary system and musculoskeletal system. 

(References are available in detailed literature reports below)

Detailed Anatomy Notes

Source Information

• Bears do not have any major anatomical specialisations.

Brain:

• Total brain volume 345,250 mm³; neocortex volume 252,159 mm³. (J373.104.w1)

Reproductive Male:

• Testis diameter 24.5 +/- 3.8 mm. (P9.2004.w5)
• 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:

• Female bears have an os clitoris. (J332.69.w1)

Gastro-intestinal system:

• Bears have a much more heavily muscled pylorus (stomach exit) than other mammals. (P85.1.w4)
• Bears lack a caecum. (B399.3.w3)
• 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)

Urinary system:

• The kidneys of bears are lobulated. (B399.3.w3)

Musculoskeletal system:

• In the sun bear, compared to Ursus arctos - Brown bear and Ursus maritimus - Polar bear, which are less arboreal in habits, the tibialis cranialis muscle possesses a more well-developed large fleshy portion from the proximal to the distal end of the tibia and a shorter tendon attaching to the proximal end of the Ossa metatarsalis. This muscle acts in flexion of the tarsal joints (dorsiflexion of the foot) and in foot supination (by lifting its medial border); the short tendon may improve joint stability. Additionally, the popliteus muscle is attached at a more distal site on the tibia compared to the other two species; this may, by leverage, induce effective pronation of the crus. (J458.187.w1)