Comparative Anatomical Studies on the Hand of Human and Two Mammalian Species

Background: Morphologically there is a great similarity in the musculoskeletal pattern in different species of the primates especially the development of hands and digits for better functional adaptation to their environment. The factors involved in evolution of modern hand are muscle-tendon architecture, shape, size of bones and articular surfaces in joints. Human hand is functionally highly evolved with manipulative potential for fast and fine skilled activity especially in thumb and index finger as compared with other species.

Aim: Present study was undertaken to compare the hand anatomy of the Baboon and Squirrel with the Human.

Methods: Two commonly found mammals in Saudi Arabia i.e. Baboon and Squirrel were selected to reflect the different environmental adaptations. The human hands were provided by the Department of Anatomy. The animals were anesthetized, sacrificed at Anesthesia Department. Fixation done by 9% formaldehyde solution, hands dissected under Zeiss dissecting microscope, Muscle groups identified using 5% iodine stain, Bones and cartilages stained by Alizarin red and Alcian blue stain respectively and photographed (Nikon D3200 digital camera). The hand divided into four parts: Wrist, dorsum of hand, palm and fingers.

Results: Human Hand: Wrist is wide, bones arranged in two rows gliding over each other for free movements at hand. Dorsum has thin fatty layer, more wrinkles and fewer hairs. Palm has thick skin without hair and well-developed muscles are arranged in groups (Thenar, Hypothenar, Lumbricals and Interossei). Digits have extensor and flexor tendons up to middle and distal phalanx. Thumb is rotated providing opposition and multiaxial movements.

Baboon Hand: Wrist is short, bones arranged in two rows but fewer movements at hand. Dorsum has fewer wrinkles, more hairs. Palm skin has very thick layer, especially at friction pad located below fingers; muscles are arranged in groups but not fully developed as compared to human.

Squirrel Hand: Small and close dimensions, five short fingers, pointed, every finger ends with a claw. The skin is thin, covered with hair. Palm is thin but completely free of hair with digital pad. Phalanges are short and all fingers have two phalanges. Thumb has only one phalanx.

Conclusions: Human hand structure is evolved for better grip and fine movements of hand providing better functional and artistic capabilities.