THE POSTERIOR LIMBS. 



149 



The principal, large, or median metatarsal bone, is longer than the same 

 metacarpal, and its body, instead of being slightly compressed before and behind, 

 is nearly a regular cylinder. It presents, outwardly, a fissure which is directed 

 at first obliquely backwards and downwards (Fig. 99), and afterwards descends 

 vertically along the lateral external metatarsal bone. The articular surface of 

 the superior extremity is excavated in its centre by a large fossa for insertion 

 (Fig. 99). This surface presents, behind and outwards, a 

 thick tubercle which appears to spring from the body of the Fig. 102. 



bone, and which has a facet against which the external rudi- 

 mentary metatarsal rests. The inferior extremity is at the 

 same time wider and thicker than that of the metacarpus. 

 Above and in front of the articular surface, it is hollowed 

 by a small transverse fossa, which is deeper than in the corre- 

 sponding bone in the anterior limb. 



Of the tivo rudimentary {digital, splint), or lateral meta- 

 tarsal bones, the external is always longest, if not thickest. 

 The internal bears on the superior face of its head three 

 articular facets, two of which articulate with the small 

 cuneiform, and the third with the large bone of that name. 



The length of these rudimentary metatarsals is nearly 

 equal to three-fourths that of the principal metatarsal. 



The metatarsus of the Ass is remarkable for the length 

 of its rudimentary metatarsals, which are nearly five-sixths 

 that of the principal bone. The latter is also notable, 

 because of its length and fineness ; and if it is compared 

 with that of the Horse, it is distinguished by : 1. The tri- 

 angular shape of its upper extremity, due to the great 

 development of the tubercle on which the external rudi- 

 mentary metatarsal lies. 2. The flat diarthrodial facet which 

 articulates with the antero-external part of the large cunei- 

 form, 3. The marked inequality of its condyles. 



Differential Characters in the Metatarsal Bones of the 

 OTHER Animals. 



posterior aspect op 

 left metatarsus. 



1, Head of principal 

 metatarsal bone ; 2, 



3, external and in- 

 ternal splint bones, 

 or metatarsals of the 

 rudimentary digits ; 



4, rough surface for 

 insertion of suspen- 

 sory ligament ; 5, 

 nutrient foramen ; 

 6, middle ridge or 

 tenon of inferior arti- 

 cular surface. 



The metatarsus is also a region in which the number of bones varies 

 in the domesticated animals. Tlius, in Ruminants there are two, and 

 five in the Pig, Camivora, and Rodents. 



The metatarsals of the latter are exactly like the same bones in 

 the anterior limb. Those of Ruminants are slightly different. 



A. Ox, Sheep, Goat.— In the Ox, Sheep, and Goat are found a 

 principal and a rudimentary metatarsal bone. The latter is a small 

 lenticular bone, articulating, posteriorly, with the head of the large 

 metatarsal bone. The latter differs from the principal metacarpal 

 bone, in being longer, quadrilateral in form, and having a vascular 

 canal traversing the posterior face of its upper extremity. 



B. Camel. — The metatarsus differs from the metacarpus by its greater width and less 

 thickness; the articular surface is divided by a depression into two parts, situated on the same 

 horizontal plane. 



C. Pig.— The Pig has four perfect metatarsals, and an internal rudimentary one. The 

 latter is a small bone flattened on both sides, articulating by means of a diarthrodial facet, and 

 sometimes fused posteriorly with the upper end of the fourth metatarsal. 



D. Dog, Cat.— Ill the Dog and Cat are one rudimentarv and four perfect metatarsals. 

 The former is articulated with the internal cuneiform, and represents the vestige of the thumb. 



