12 



MAMMALIA 



ridge. The shaft is flattened on the back side. The upper end of the 

 anterior surface is raised in a narrow ridge, the procnemial crest {en), while 



the lower end is ex- 

 panded on a broad arti- 

 cular facet, which latter 

 may be divided into two 

 portions by a median 

 ridge, while the inner 

 boundary is also raised 

 to make the malleolus 

 internus [mi). The 

 fibula {fi) is always a 

 slender bone, the lower 

 end (co) of which is often 

 prolonged into a process 

 corresponding to the 

 malleolus internus, and 

 resting on the outer sur- 

 face of the astragalus or 

 calcaneum. In front of 

 the articulation between 

 the femur and the tibia 

 is a small patella {Pa) 

 connected by ligaments 

 with the tibia. 



Right pes of Palaeotherium (A), of the pig (B), and of Hipparion ^"^ the CaSC Of the 



(C). ca and c, Calcaneum ; a, astragalus ; n, navicular ; ob, cuboid ; ci, CarpUS, the ankle Or tarSUS 



c2, c3, cuneiform, primum, secundum, tertium : m, metatarsals: II. -V., /tt -, a \ • . r . 



second to fifth digits. ' (l^lg. 14) COnSlStS 01 twO 



rows of bones, between 

 which there is always a well-developed centrale or navicular. The upper row 

 consists of the astragalus ( = tibiale plus intermedium ^) on the inner side ; 



C D 



Fig. 15. 



Left astragalus of the dog, A from front and above, B from behind and below ; and left astragalus of a laige 

 ruminant (Htlladotherium), C from front and above, D from behind and below, half nat. size (after Gaudry). 

 t. Tibial facet (trochlea) ; c, c', lateral border for articulation with calcaneum ; ca?, facet for calcaneum ; a, fossa 

 for reception of lower border of tibia ; n, facet for navicular ; cub, facet for cuboid. 



and the calcaneum ( = fibulare) on the outer side. The astragalus articulates 

 with the tibia to make the ankle joint. The anterior and upper articular 



^ The astragalus is more probably homologous with the enlarged iutermedium, as in Permian 

 reptiles, the tibiale having beeu lost. 



