THE FROG. 193 



line ; and a corresponding bone (the omosternum) extends 

 anteriorly from the point of union of the two clavicles. 



What attachment is there between the shoulder girdle 

 and the spinal column ? 



IV. Bones of the Hind Limb. The bones of the hind 

 limb are as follows : 



1. The single bone of the thigh is the femur. 



2. The bone of the shank is the os cruris. It is made 

 up of two bones, tibia and fibula, as indicated by the lon- 

 gitudinal grooves near its ends. 



In the bones of the foot, three series may be distin- 

 guished, of which the first consists of two long, curved 

 tarsal bones, united at their cartilaginous tips. The other 

 two series are called metatarsal and phalanges, and corre- 

 spond in position and appearance to homologous parts of 

 the hand. 



V. The Pelvic Girdle. Study the pelvic girdle. Ob- 

 serve its shape, position, and attachment to the spinal 

 column. Its halves are very solidly welded together on 

 the median line. Each half is composed of three bones, 

 united about the socket (acetabulum), into which the head 

 of the femur fits ; and the bones, though solidly coherent, 

 may be distinguished by examining the lateral surface at 

 their point of union. (1) The long bone extended ante- 

 riorly to meet the lateral process from the ninth vertebra, 

 and shaped like an inverted sled runner, is the ilium. 

 (2) The bone that forms the ventral fifth of the socket 

 (acetabulum), and, with its fellow, forms the ventral ridge 

 of the pelvic girdle, is the pubis. (3) The bone that 

 forms the posterior two fifths of the socket, and, with 

 its fellow of the opposite side, forms the posterior ridge 

 of the girdle, is the ischium. 



Compare now shoulder and pelvic girdle, and fore and 

 hind limb, and note the principal points of likeness and 

 of difference between them. 



NEED. ZOOL. 13 



