THE OSTEOLOGY OF VULPES MACROTIS. 415 



Vulpes macrotis, in common with other terrestrial carnivores, has the skeleton 

 of pes divided into three parts, namely, the tarsus, the metatarsus, and the digits 

 or phalanges. The tarsus is composed of seven distinct bones articulating with 

 each other in a manner similar to what is known to occur in the tarsi of other 

 representatives of this group. These bones are the astralagus, the os calcis or 

 calcaneum, the scaphoid or navicular bone, the three cuneiform bones (internal, 

 middle and external), and the cuboid. 



Morphologically, the astralagus is composed of the tibiale and the intermedium, 

 the internal cuneiform is the first tarsal (tarsale I), the middle the second, the 

 external the third, and the cuboid the united fourth and fifth tarsals (tarsale IV 

 and V). 



The metatarsus of V. macrotis consists of four much elongated metatarsal 

 bones, of a very rudimentary, hook-like hallux, only 4.5 mm. long, and freely 

 articulating with the anterior facet upon the internal cuneiform. On the under 

 side of each distal trochlear extremity of the fully developed metatarsal bones we 

 find a pair of large sesamoids. Each pair of these sesamoids is so disposed as to give 

 the appearance of being but a single one, deeply grooved in the longitudinal direc- 

 tion, both on the dorsal as well as the ventral aspects. They are in the plantar 

 tendons of pes. The podal phalanges closely resemble those of the manus, and 

 have bones of the same number, and nearly of the same form and size. Great 

 beauty of adaptation and movement characterizes the ankle-joint of this fox, 

 especially in its articulation with the bones of the leg. 



The astragalus is a very irregularly formed bone, consisting of a trochlear 

 portion and head. The latter is a cuboidal projection that extends forward from 

 the antero-internal aspect of the former, and has its distal, vertical face entirely 

 occupied by a slightly convex, smooth facet for articulation with the navicular bone 

 or scaphoid. Seen from above, the trochlear part of the astragalus has a most 

 perfect articulation of that character, reminding one at once of the distal end of a 

 phalanx in the manus of Homo, or in the pes of any large true raptorial bird. 

 Its median groove is longitudinal, and extends from the head of the bone backward 

 clear around and under for some distance, making in all a beautiful curved surface. 

 The' lateral margins are somewhat sharp, especially the inner one, which in the 

 articulated ankle fits into the little narrow and deep notch which was described 

 above as being found on the anterior distal margin of the basal part of the tibia. 

 This admirable arrangement prevents to a great degree the danger of the lateral 

 dislocation of the bones of the leg and the tarsus from any violence or sudden 

 sprain in running. 



On the under side of the astragalus there is a somewhat irregular trochlea for 

 articulation with the os calcis. Its convexity is transverse or just the reverse of 

 the one on the upper side of the bone. Furthermore we find here a minute longi- 

 tudinal groove passing toward the head of the bone, but with its posterior extemity 

 terminating in a deep pitlet. Internally, the surface of the astragalus is extensive 

 and undulating; externally, it is narrow and markedly curved, the curve corre- 



