THE PHALANGES. 



227 



interossei 



in. 



Phalanx, 

 ungual or 

 terminal 



II. Phalanx 



the collateral ligaments of the metacarpo-phalangeal joint, and also to the 

 muscles. The distal end is much smaller than the 

 proximal; the convex articular surface is divided into 

 two condyles by a central groove. 



Phalanx Secunda. The second phalanx resembles 

 the first in general form, but is of smaller size. It 

 differs, however, in the form of its proximal articular 

 surface, which is not a simple oval concavity, but is an 

 oval area divided into two small, nearly circular con- 

 cavities by a central ridge passing from volar to dorsal edge ; 

 these articulate with the condylic surfaces of the proximal 

 phalanx. Into the margins of its volar surface near 

 the proximal end are inserted the split portions of the 

 tendon of the flexor digitorum sublimis, whilst on the 

 dorsal aspect of the proximal end the central slip of the 

 extensor digitorum communis muscle is attached. 



Phalanx Tertia. The third or terminal or ungual 

 phalanx is the smallest of the three ; it is easily recognised 

 by the spatula-shaped surface on its distal extremity which 

 supports the nail. The articular surface on its proximal 

 end resembles that on the proximal end of the second 

 phalanx, but is smaller. On the volar aspect of this 

 end of the bone there is a rough surface for the insertion 

 of the tendon of the flexor digitorum profundus muscle. 

 The dorsal surface of the same extremity has attached to 

 it the terminal portions of the tendon of the extensor 

 digitorum communis muscle. The phalanges of the 

 thumb resemble in the arrangement of their parts the 

 first and third phalanges of the fingers. 



The arterial canals, usually two in number, placed on either 

 side of the volar aspect and nearer the distal than the proximal 



end of the bone, are directed towards the finger-tips. FIG. 227. THE PHALANGES OF 



THE FINGERS (Volar Aspect). 



Ossification. The phalanges are ossified from primary 

 and secondary centres. From the former, which appear as early as the ninth week of 



I. Phalanx 



Shaft 



Hi 



' 



f 



FIG. 228. RADIOGRAPHS OF FOETAL HANDS. 



1. About ten weeks. Here the ossific nuclei of the terminal phalanges and the medial four metacarpal bones 



are seen. . , 



2. A little later. The centre for the metacarpal for the thumb is now present, as also the centres for the proximal 



row of phalanges. The centres of the medial row of phalanges have appeared in the case of the nude 

 and ring fingers. 



3. During the third month. All the primary centres for the metacarpal bones and phalanges are 



developed. 



4. About the fourth to fifth month. 



5. About the sixth to seventh month. 



foetal life, the body and distal extremities are developed ; whilst the latter, which begin 

 to appear about the third year, form the proximal epiphyses which unite with the bodies 



15 a 



