206 THE ARTICULATIONS. 



r. The lateral sesamoid ligaments are two thin layers, extending from the 

 external face of each sesamoid to the tubercle of insertion on the side of the 

 superior extremity of the firet phalanx (Fig. 131, a 2). They are covered by the 

 digital vessels and nerves, by the fibrous stay detached from the suspensory liga- 

 ment to the anterior extensor tendon of the phalanges, and by the supei^ficial 

 fasciculus of the lateral metacarpo- phalangeal ligament ; they are covered by 

 synovial membrane on their internal face. 



B. The ligaments destined to unite the two articular surfaces of the meta- 

 carpo-phalangeal joint are four : two lateral, one anterior, and one posterior. 



a. Each lateral ligament comprises two fasciculi — a supei'ficial and a deep — 

 firmly united by their adjacent faces. The supei'ficial fasciculus (Fig. 132, 12) 

 commences on the button of the lateral metacai-pal bone, attaches itself to the 

 median metacai-pal, and descends vertically to terminate at the superior extremity 

 of the first phalanx. It covers the phalangeal insertion of the lateral sesamoid 

 ligament and the deep fasciculus. The latter, attached superiorly in the lateral 

 excavation of the inferior extremity of the principal metacarpal, radiates as it 

 reaches the sesamoid and the superior extremity of the first phalanx, where it is 

 fixed by mixing its fibres with those of the lateral sesamoid ligament. The inner 

 face of this fasciculus is lined by the articular synovial membrane (Fig. 132, 12'). 



h. The anterior ligament (Fig. 132) belongs to the class of capsular ligaments. 

 It is a veiy resisting membmniform expansion, which envelops the anterior face 

 of the articulation. Attached by its upper border to the anterior margin of the 

 metacarpal surface, and by its inferior border to the fii^st phalanx, this expansion 

 is confounded at its sides with the lateral ligaments. It is covered by the extensor 

 tendons of the phalanges, which glide on its surface by means of small serous 

 sacs. Its internal face adheres throughout its whole extent to the synovial 

 capsule. 



c. The posterior ligament,^ very appropriately named the suspensory ligament 

 of the fetlock (Figs. 132, 6 ; 133, 134, 4), is a long and powerful brace, composed 

 of white fibrous tissue, and often containing fasciculi of fleshy fibres in its texture. 

 Lodged behind the median metacarpal, and between the two lateral metacai'pal 

 bones, this brace is quite thin at its origin, but it soon becomes enlarged, and pre- 

 serves its great thickness to the extent of its upper fourth. Examined in section, 

 it appears to be formed of two superposed portions which are closely adherent to 

 each other. The superficial portion, the thinnest, commences by three small 

 branches, which are fixed to the first and second bones of the lower carpal row 

 (Figs. 132, 133, 5) ; the deep portion, much thicker, is attached to the posterior 

 face of the principal metacai'pal for about ^ of an inch. It has been 

 wrongly asserted that the suspensoi'y ligament of the fetlock is continuous with 

 the common posterior ligament of the cai'pus ; it is, on the conti'ai'y, quite distinct 

 from it. The carpal stay {deep palmar aponeurosis of Man) is alone in direct 

 continuity with the common posterior ligament of the cai'pus (133, 3). The 

 suspensory ligament of the fetlock is bifid at its inferior extremity ; its two 

 branches, after being fixed into the summits of the sesamoid bones, give origin to 

 two fibrous bands which pass downwards and forwards to become united on each 

 side to the anterior extensor tendon of the phalanges (Fig. 132, 9). It is in relation, 

 by its posterior face, with the perforans tendon and its cai-pal stay ; by its anterior 

 face, with the median metacarpal bone, and arteries and veins ; by its borders, 



' It corresponds to the two muscles which, in Man, lie alongside the interosseous meta- 

 carpal muscles. (See Muscles of the Foot.) 



