124 



THE SKELETON OF THE HORSE 



difference is about two inches. The shaft is more cylindrical, and is almost cir- 

 cular on cross-section, except in its distal part. At the proximal part of its lateral 

 surface there is a groove, which is directed obhquely downward and backward, and 

 is continued by the furrow formed by the apposition of the fourth or lateral meta- 

 tarsal bone ; it indicates the course of the great metatarsal artery. A shallow im- 

 pression in a similar place on the medial side marks the position of the corresponding 



vein. The nutrient foramen is rela- 

 tively higher than on the metacar- 

 pal bone. The proximal extremity 

 is much wider from before back- 

 ward than that of the metacarpal 

 bone. Its articular surface is 

 slightly concave, and is marked 

 by a large central non-articular de- 

 pression, continued outward by a 

 deep notch. The greater part of 

 the surface articulates with the 

 third tarsal, but there is a lateral 

 facet for the fourth, and usually a 

 small facet postero-medially 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 lateral side behind the vascular 

 groove. The distal extremity closely resembles that of the corresponding meta- 

 carpal bone. 



In some cases the distal part of the shaft is bent backward somewhat. The distal articular 

 surface extends a Mttle higher behind than in the case of the metacarpal bone. The large meta- 

 tarsal bone is even more strongly constructed than the metacarpal. The shell of compact sub- 

 stance is very thick in the middle of the shaft, especially in front and medially. 



Fig. 114. 

 Figs. 114, 115.- 



Fig. 115. 



■Choss-sections of Left Metacarpal and 

 Metatarsal Bones. 

 Sectiona are cut a little above middle of bones. 



Fig. 116. — Third Phalanx of Thoracic Limb op Horse. Fig. 117. — Third Phaunx of Pelvic Limb of Horse. 



The small metatarsal bones (Ossa metatarsalia secundum et quartum) are a 

 little longer than the corresponding metacarpals. The lateral (fourth) metatarsal 

 bone is relatively massive, especially in its upper part. The head is large and out- 

 standing, and bears one or two facets above for the fourth tarsal, and two in front 

 and medially for articulation with the large metatarsal; elsewhere it is roughened 

 for attachment. The medial (second) metatarsal bone is much more slender than 

 the lateral one, especially in its proximal part. The head bears two facets above for 

 the first and second tarsals, and sometimes one for the third tarsal. 



