MAMMALIA 269 



The metacarpal bones are five in number and are related 

 to the carpalia as shown above the medial one being that of 

 the thumb, and the phalanges are the same in number as those 

 of the human hand, viz. 2, 3, 3, 3, 3. The terminal phalanx 

 in each is enclosed in the long horny claw developed from the 

 epidermis, and, like the claw, it is long, tapering, and curved. 

 Sesamoid bones are developed in association with the flexor 

 tendons below the joints of the hand, and may be well seen in 

 the larger skeletons. 



The pelvic girdle is formed of two innominate bones which 

 meet ventrally and are united by cartilage, the symphysis, 

 and are separated above by the sacrum. Each innominate 

 consists of (1) the ilium, the forwardly directed element which 

 after articulation with the sacrum expands into a strong 

 gluteal surface and crest. It forms the anterior part of the 

 acetabulum. It is joined there dorsally by (2) the ischium, 

 which extends backwards, forming the ischial crest and spine, 

 and is continued downwards to meet its neighbour below. The 

 acetabulum is completed ventrally by (3) the pubis, which is 

 directed ventrally to meet its neighbour and to fuse with the 

 ischium, thus completing the arch enclosing the obturator 

 foramen. The two pubes in the rabbit aie united by cartilage, 

 the joint being called the symphysis pubis. The ischium in 

 many mammals is also involved in the symphysis. In the 

 adult these three bones are firmly fused together, but in the 

 young they are separated, and they are developed independ- 

 ently, remaining connected by cartilage which permits of 

 growth. A small bone is present in this cartilage, the cotyloid 

 bone, and it subsequently fuses with the pubis. 



The femur is articulated to the innominate by its projecting 

 rounded head, which fits into the deep cavity of the acetabulum. 

 The upper extremity of the bone is produced externally into 

 the great trochanter. On the ventral aspect of the head there 

 is a smaller process, the lesser trochanter ; and further down, 

 in the case of the rabbit, is a third trochanter, a process 

 which it will be observed is well developed on the femur of 

 the horse and its allies. The lower extremity is expanded to 

 form condyles which bear below articular surfaces for the tibia. 

 Between the condyles a groove, the patellar groove, receives 



