THE PHALANGES AND SESAMOIDS 111 



marks the position of the corresponding vein. The nutrient foramen is relatively 

 higher than on the metacarpal bone. The proximal extremity is much wider from 

 before backward than that of the metacarpal bone. Its articular surface is sHghtly 

 concave, and is marked by a large central non-articular depression, continued out- 

 ward by a deep notch. The greater part of the surface articulates with the third 

 tarsal, but there is an outer facet for the fourth, and usually a small facet postero- 

 internally for the second tarsal bone. Posteriorly there are two pairs of facets for 

 articulation with the small metatarsal bones. The front is crossed by a rough ridge 

 for insertion, which becomes larger and turns downward on the outer side behind the 

 vascular groove. The distal extremity closely resembles that of the corresponding 

 metacarpal bone. 



In some cases the lower part of the shaft is bent backward somewhat. The articular sur- 

 face extends a little higher behind than in the case of the metacarpal bone. The large metatarsal 

 bone is even more strongly constructed than the metacarpal. The shell of compact substance is 

 very thick in the middle of the shaft, especially in front and internally. 



The small metatarsal bones are a little longer than the corresponding meta- 

 carpals. The external (fourth) metatarsal is relatively massive, especially in its 

 up])er part. The head is large and outstanding, and bears two facets alcove for the 

 fourth tarsal, and two in front and internally for articulation with the large meta- 

 tarsal; elsewhere it is roughened for attachment. The internal (second) meta- 

 tarsal is much more slender than the outer one, especially in its upper part. The 

 head bears two facets above for the first and second tarsals, and sometimes one for 

 the third tarsal. 



THE PHALANGES AND SESAMOIDS 



The axis of the phalanges of the hind liml) is about five degrees less oblique 

 than that of the fore limb, and the chief differences in the form and size of the bones 

 are as follows : 



The first phalanx is a little shorter, wider above, and narrower below. 



The second phalanx is narrower and slightly longer. 



The third phalanx is narrower, the angle of inclination of the wall surface is a 

 little (ca. 5 degrees) greater, the sole surface is more concave, and the wings are 

 less prominent and closer together. 



The proximal sesamoids are a little smaller, except in thickness. The third 

 sesamoid or navicular bone is narrower and shorter. 



