208 COMPARATIVE ARTHROLOGY 



which join the tendons of the proper extensors of the digits; it sends fibers also to 

 the interdigital lateral ligaments and to the central sesamoids. About the middle 

 of the metacarpus the suspensory ligament detaches a band which unites lower 

 down with the superficial flexor tendon, thus inclosing the tendon of the deep flexor 

 of the digit; it also blends with the thick fascia of the region. The latter gives off 

 a band on either side to the accessory digits, and a tendinous band descends from 

 each accessory digit to the third phalanx and sesamoid bone, blending with the 

 tendon of the corresponding proper extensor. 



Pig. — There are four metacarpo-phalangeal joints, each of which has a capsule, 

 lateral, intersesamoidean, and crucial sesamoidean ligaments. Since distinct inter- 

 osseous muscles are present, there are, of course, no suspensory ligaments. 



Dog. — There are five metacarpo-phalangeal joints, each having its own capsule 

 and indistinct lateral ligaments. A small sesamoid bone occurs in the anterior 

 part of each capsule, over which the corresponding extensor tendon plays. The 

 intersesamoidean ligaments do not extend above the sesamoids. The cruciate 

 ligaments are present, as well as a fibrous layer which attaches the distal margins 

 of the sesamoids to the posterior surface of the proximal end of the first phalanx. 



INTERPHALANGEAL JOINTS 



Ox. — The two proximal joints have separate capsules, and broad, but rather 

 indistinct, lateral ligaments. Each joint has also two central and two lateral volar 

 ligaments. The central ligaments are largely fused to form a strong band. The 

 lateral ones extend from the borders of the first phalanx to the proximal end of the 

 second phalanx. 



The distal interphalangeal joints have, in addition to the capsules and lateral 

 ligaments, bands which reinforce them on either side. The central or interdigital 

 pair arise in the depressions on the distal ends of the first phalanges, receive fibers 

 from the second phalanges, and end on the interdigital surfaces of the third phal- 

 anges at the margin of the articular surface. The lateral pair have a similar course, 

 but are thinner, and end on the corresponding third sesamoid. An elastic band 

 crosses the front of the second phalanx obliquely, from the distal end of the first 

 phalanx to the extensor process of the third phalanx. 



The crucial or inferior interdigital ligaments (Ligamenta cruciata interdigitalia) 

 are two strong bands which limit the separation of the digits. They are attached 

 above to the lateral (or abaxial) eminences on the proximal ends of the second 

 phalanges (blending with the lateral ligaments), cross the deep flexor tendon 

 obliquely, and reach the interdigital space, where they intercross and blend. Most 

 of the fibers end on the third sesamoid of the opposite side, but some are attached 

 to the interdigital aspect of the second phalanx and the third sesamoid of the same 

 side. In the sheep there is, instead of the foregoing, a transverse ligament which 

 is attached on either side to the interdigital surfaces of the second and third phalanges 

 and the third sesamoid bone. It is related below to the skin, above to a pad of fat. 



Pig. — The interphalangeal joints of the chief digits resemble in general those 

 of the ox. The inferior interdigital ligament resembles, however, that of the sheep, 

 and is intimately adherent to th(^ skin. There is, besides, a remarkable arrange- 

 ment of ligaments which connect the small digits with each other and with the 

 chief digits. 



This apparatus is somewhat complex, but its chief features are as follows: A superior inter- 

 digital ligament is attached on either side to the third phalanges of the small digits, while centrally 

 it blends with the annular ligaments of the flexor tendons behind the metacarpo-phalangeal 

 joints of the chief digits. Two bands (central longitudinal interdigital ligaments) arise on the 

 bases of the small digits, cross the flexor tendons ol)liquely downward and inward, pass through 

 the superior interdigital ligament, and blend below with the inferior interdigital ligament. Two 

 lateral bands (lateral longitudinal interdigital ligaments) are attached in common with the 



