FREE APPENDAGES MAMMALS 293 



As in Plesiosaurs and Ichthyosaurs the number of digital bones may be 

 increased in whales, not by multiplication of phalanges, but by the retention of 

 separate epiphyses through life. 



The femur, relatively short in Monotremes, Ungulates, seals and 

 whales, usually has a hemispherical head on a short neck which 

 extends at an angle with the shaft, but in Monotremes and some 

 Ungulates and Edentates it is in Hne with the axis of the bone. 

 Major and minor trochanters are variously developed, and a third 

 trochanter, common in Perissodactyls, Insectivores, some Edentates, 

 rodents, etc., may be connected with the major trochanter by a long 

 (gluteal) crest. Distally the femur has two condyles, lateral and 

 medial, for articulation with the crural bones, the tibial connecting 

 with both, the fibula, when not fused with the tibia, articulating with 

 the lateral condyle. There is usually a patella at the knee (small 

 in Carnivores, possibly lacking in some Marsupials) and there may 

 be similar bones (fabellae) in the genal angle. 



The tibia is always the larger of the two crural bones, the fibula 

 is often greatly reduced. These two bones are parallel, no twisting 

 occurring, and they have but sHght motion on each other, the 

 extreme occurring in some Marsupials with opposable great toe, 

 when there may be shght rotation. Partial fusion of the two, espe- 

 cially at the ends, is common. The tibia has two articular surfaces 

 for the two femoral condyles; distally it articulates with the talus, 

 and medial to the articulation it sends a process (medial malleolus) 

 down on the medial side of the ankle. Usually the fibula does not 

 reach the femur and its lower end often falls short of the tarsus. It is 

 most reduced in bats where its distal end, fused with the tibia, forms 

 a lateral malleolus (occurring also in other orders), the two malleoh 

 strengthening the tarsal joint. 



The tarsus is usually short Tar sins (fig. 324) and some lemurs 

 excepted. There are two bones in the proximal row, a median talus 

 (astragalus) and a lateral calcaneus. The former is usually fused 

 tibiale and intermedium, the latter the fibulare, but in some species 

 the talus may include the centrale (tri tibiale), or the latter may fuse 

 with the calcaneum. The intratarsal joint of the Sauropsida does 

 not occur in mammals, the hinge being between the crural and 

 proximal tarsal bones, talus and tibia being most concerned, fibula 

 and calcaneus articulating only in Aplacentals and a few others. The 



