OSTEOLOGY AND ARTHROLOGY 99 



We have already mentioned that the scaphoid and the 

 cuboid are ankylosed ; they form by their union an irregular 

 bone, on which the astragalus and calcaneum are sup- 

 ported. 



The cuneiforms articulate with the internal half of the 

 superior extremity of the principal metatarsal ; the ex- 

 ternal half of this metatarsal articulates with the portion of 

 bone which represents the cuboid. 



The metatarsus is represented by a principal metatarsal, 

 formed by the coalescence of two metatarsals ; we also find 

 in this region a very small rudimentary metatarsal. 



The metatarsus is a little longer than the metacarpus ; its 

 transverse measurement is a little less ; on the other hand, 

 it is a little thicker in antero-posterior direction ; from these 

 two differences it results that the body of the metatarsus 

 is quadrilateral, whereas the metacarpus presents only an 

 anterior and a posterior surface. 



The rudimentary metatarsal is a very small roundish 

 bone, situated at the back of the superior extremity of the 

 principal metatarsal. 



The phalanges closely resemble those of the anterior limbs ; 

 nevertheless, the first and second phalanges differ from the 

 latter in the fact that they are a little longer and narrower. 



At the back of the metatarso-phalangeal articulations, as 

 in the corresponding region of the anterior limbs, are found 

 the sesamoid bones. Such also exist at the articulations of 

 the second and third phalanges. 



Unguligrades: Horse (Fig. 40, p. 64). — The pelvis of 

 the horse presents a general form which sharply differentiates 

 it from that of the carnivora ; in fact, the ilium is twisted in 

 such a way that the external iliac fossa does not look outwards, 

 but upwards. It results from this twist that the anterior 

 iliac spine, which we have seen to be directed downwards in 

 the carnivora, has become external ; and this prominence is 

 much farther removed from the vertebral column than in 

 the dog or cat. On the other hand, the posterior iliac spine, 

 which is directed upwards in the carnivora, has become 

 internal ; it is also placed nearer to the vertebral column, 

 with the result that the distance which separates this spine 



7—2 



