THORACIC LIMBS 



645 



FIG. 509. 



Sew 



the flexor profundus digitorum ; on the dorsal side are attached the 

 retractor ligaments. 



Nomenclature. Phalanx is a Greek word meaning a line of 

 soldiers in battle order. It was used by Aristotle because of the 

 arrangement of the elements of each finger in a row. Strictly 

 speaking, the whole digit would be a phalanx, but the word became 

 restricted to each element of the finger. The actual joints of the 

 fingers have been known as nodi, or knobs, and the short bones which 

 form the joints, the phalanges, have been called internodia, as we see 

 in the name of the muscle extensor primi internodii pollicis, the 

 extensor of the first phalanx of the thumb. 



SESAMOID BONES OF THE HAND. 



The hand possesses, in addition to the twenty-six bones already 

 described, eleven small ossicles which are developed in tendons. One 

 of these is found in the tendon of the abductor 

 pollicis muscle, closely applied to the radial end of 

 the scapho-lunar. It is a very small bone, with 

 a circular outline, a convex outer surface, and a 

 smooth inner surface, which is covered with car- 

 tilage and applied to the facet on the dorsal side 

 of the process of the scapho-lunar. 



The remaining ten sesamoids are in five pairs, 

 a pair on the palmar side of the metacarpo- 

 phalangeal joint of every digit, where they 

 furnish protection to the joint and serve for the 

 attachment of muscles and ligaments. 



Every one of these sesamoids has the shape of 

 a cocked hat, presenting a dorsal, a medial, and a 

 lateral surface. 



The dorsal surface is narrow, and pointed at the 

 proximal end. Its lateral outline is arcuate ; the 

 medial outline is almost straight. The surface is 

 concave from the distal to the proximal end, and convex from side to 

 side. It does not face directly to the dorsal side of the hand, but dor- 

 sally and to the middle line of the finger. It encroaches, therefore, upon 

 the medial surface. The dorsal surface glides upon half of the head of 

 the metacarpal, and is separated from its fellow at the longitudinal crest. 



POSITION OF SESAMOID. 



