Veterinary Gross Anatomy

PROXIMAL SESAMOIDS

Ox

• The proximal sesamoids are a pair for each digit.
• They are situated behind the distal extremity of the large metacarpal and afford increased leverage to the flexors of the digits.
• Each bone has the form of a three-sided pyramid with the base below and the apex above. The base presents a facet for the first phalanx. The dorsal surface articulates with the distal extremity of the large metacarpal on its volar aspect.
• Each sesamoid also presents a facet for articulation with a similar facet of its fellow. The abaxial and axial sesamoids of each digit articulate with each other. The opposing faces of the axial sesamoids are covered in life by fibrocartilage and form a groove for the gliding of the deep flexor tendon of the digit.

Sheep and Goat 

• The number similar to that of an ox.
• The abaxial ones are compressed from side to side and the axial ones are compressed from before backwards.

Horse

• There is only one digit (third) and hence one pair of proximal sesamoids.
• Each is much larger and distinctly pyramidal in shape.
• It articulates only with the large metacarpal but neither with the first phalanx nor with its fellow. The abaxial surface is concave.  

Pig

•  Similar to that of an ox.

Dog 

•  Nine proximal sesamoids are present; one for the first digit and two for each for the other digits.
• Besides, there is a dorsal sesamoid in the capsule of each metacarpo-phalangeal joint.

Rabbit 

• Many proximal sesamoid bones on the metacarpo-phalangeal joints.

Fowl

• The sesamoids are absent.