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 obliquely 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 
Fig. 114. Fig. 115. deep notch. The greater part of 
Fias. 114, 115.—Cross-sections or Lerr MerTACARPAL AND the surface articulates with the 
Merararsat Bones. third tarsal, but there is a lateral 
Sections are cut a little above middle of bones. 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 eases the distal part of the shaft is bent backward somewhat. The distal articular 
surface extends a little 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. 
Fic. 116.—Tutrp Paatanx or Tooracic Limp or Horse. Fia. 117.—Turrp PHatanx or Petyic Limp or 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. 
