666 MAMMALIA. 



In Mammals the fourth and fifth carpals are always fiised ; the cen- 

 trale is often absent. In the tendons of the flexor muscles there are 

 often two sesamoid bones, of which the ulnar is called the pisiform. 



In the rabbit there are five metacarpal bones and five digits, each 

 with three phalanges except the thumb or poUex which has but two. 



The pelvic girdle is articulated to the backbone, and bears 

 externally a cup-like socket or acetabulum in which the 

 head of the thigh bone works. Each half of the girdle — 

 forming what is called the innominate bone — really consists 

 of three bones which meet in the acetabulum. The dorsal 

 bone or ilium, which corresponds to the scapula, articulates 

 with the sacral vertebra ; the pubis — the anterior of the tsvo 

 lower bones — unites with its fellow on the opposite side in 

 the pubic symphysis ; the two ischia, which correspond to 

 the coracoids, extend backwards, separated from the pubes 

 by the large obturator foramen, and expand into posterior 

 tuberosities. The ischia of mammals may touch one another 

 ventrally, but do not fuse in a symphysis ; the pubic sym- 

 physis is almost invariably present. Only in Cetacea and 

 Sirenia is the pelvis markedly rudimentary. 



The hind leg consists of a thigh or femur, a lower leg with 

 two bones — the tibia and the fibula, an ankle or tarsus, the 

 sole bones or metatarsals, the toes with several joints or 

 phalanges. 



The head of the femur works in the acetabulum of the pelvis. Near 

 the head are several processes or trochanters, serving for the insertion of 

 muscles ; in the rabbit there are three — the great trochanter, the lesser 

 trochanter, and the third trochanter. 



In front of the knee there is a sesamoid bone — the knee-pan or patella 

 — and posteriorly there are smaller fabellie. 



In tlie lower leg, the tibia, which corresponds to the radius, is pre- 

 axial, and in the normal position interior ; the fibula, which corresponds 

 to the ulna, is postaxial, and in the normal position exterior. In the 

 rabbit the fibula is slender, and is fused distally with the tibia. 



In the mammalian tarsus there are two rows of bones, and a central 

 bone interposed between the two rows on the inner or tibial side. 

 Calcaneum Astragalus 



or Fibulare. ( = Inlerraechum and Tibiale). 



Centrale 

 or Navicular. 

 Tarsale 5 and 4 Tarsale 3 Tarsale 2 Tarsale I 



= Cuboid. or or or 



External Middle Internal 



Cuneiform. Cuneiform. Cuneiform. 

 In the rabbit the first tarsal and the corresponding toe or hallux are 



