THE LIMBS OF THE HOUSE 77 



beyond their proximal limit. The surface of the ligament and the 

 adjoining surfaces of the sesamoids are covered by a veneer of fibro- 

 cartilage, and thus form a smooth, oval, groove-like area over which the 

 deep flexor tendon plays. 



The lateral and medial sesamoid ligaments (ligamentum sesamoideum 

 laterale : mediale) are partly covered by the lateral and medial collateral 

 ligaments and the limbs of the interosseous muscle. When these have 

 been reflected, the sesamoid ligaments are disclosed as short bands 

 passing from the sesamoid bones to the third metacarpal bone and the 

 first phalanx. 



The straight sesamoid ligament (ligamentum sesamoideum rectum) 

 is a strong band springing from the bases of the two sesamoid bones, 

 and, narrowing somewhat, running down the volar aspect of the first 

 phalanx to be attached to the complementary cartilage of the second 

 phalanx between the two limbs of the tendon of the superficial flexor 

 with which it is intimately connected. The straight ligament must be 

 cut across, and raised from the oblique ligaments which it partly 

 covers, and with which some of its fibres are blended. 



The oblique sesamoid ligaments (ligamenta sesamoidea obliqua) are 

 attached to the bases of the sesamoid bones and to the V-shaped line 

 on the volar surface of the first phalanx. 



If the oblique ligaments are reflected, the cruciate sesamoid ligaments 

 (ligamenta sesamoidea cruciata) are brought into view. Each of these 

 is flattened, and consists of short fibres running from the base of a 

 sesamoid bone to the back of the proximal part of the first phalanx, 

 crossing the fibres of the fellow ligament in the middle line of 

 the digit. 



Still deeper ligamentous fibres (ligamenta sesamoidea brevia) may 

 be revealed on examination of the joint from within. These are few 

 in number and oblique in direction, and are attached to the sesamoids 

 and the first phalanx close to the articular margin. 



From the character of the bony surfaces and the disposition of 

 the ligaments, it is evident that the movements in the metacarpo- 

 phalangeal joint are limited to flexion and extension. The dissector 

 cannot fail to observe that, when the weight of the body is borne by 

 the limb, the long axes of the metacarpus and the first phalanx are not 

 in the same line, and that the condition of the joint might be described 

 as one of over-extension. He will also notice that a greater degree of 

 over-extension is prevented by the attachments of the structurally 

 modified interosseous muscle to the sesamoid bones, and the morpho- 

 logical extension of the muscle to the first and second phalanges by the 

 ligaments distal to the sesamoids. In brief, the interosseous muscle 



