XIII 



PHYLUM CHORDATA 



301 



pp 



ischium (Hp Is), passes backwards from the ischiadic symphysis 



and supports the ventral wall of the cloaca. 



The hind-limb consists, like the fore-limb, of three divisions: 



these are termed respectively the proximal or femur, the middle 



or crus, and the 



distal OY pes. The 



proximal division 



consists of one 



bone, the femur ; 



the middle divi- 

 sion of two, the 



tibia and fibula ; 



the distal of the 



tarsal and meta- 



tarsal bones and 



the phalanges, 



When the limb is 



extended at right 



angles with the 



trunk, the tibia is 



pre-axial and the 



fibula post-axial : 



in the natural 



position of the 



parts the pre-axial 



border is internal in all three divisions of the limb. The femur is 



a stout bone consisting of a shaft and two epiphyses. The 



proximal epiphysis develops a rounded head which fits into the 



acetabulum ; near it on the pre-axial side is a prominence, the 



lesser trochanter, and a nearly obsolete prominence on the post- 

 axial side represents the greater 

 trochanter. The distal extremity is 

 pulley-shaped, with internal and 

 external prominences or condyles for 

 articulation with the tibia ; imme- 

 diately above the external condyle 

 is a prominence or tuberosity for 

 articulation with the fibula. The 

 tibia is a stout, curved bone, along 

 the anterior (dorsal) edge of which 

 runs a longitudinal ridge, the 

 cnemial ridge : the proximal ex- 

 tremity presents two articular sur- 

 faces for the condyles of the femur. 



The fibula is a slender bone, the proximal end articulating with 



the external tuberosity of the femur, the distal with the tarsus. 

 The tarsus (Fig. 911) comprises only three bones in the adult, 



FIG. 910. Pelvis of Lacerta vivipara. from the ventral side. 

 Ac. acetabulum ; Cep. epi-pubis : Fo'.' foramen for obturator 

 nerve ; Up. Is. hypo-ischium ; /. ilium ; 1 1, process representing 

 the pre-acetabular part of the ilium : Is. ischium ; P. pubis ; 

 PP. pre-pubis. (After Wiedersheim.) 



-tb/b 



FIG. Oil. Tarsus of Lacerta agrilis. 



/&. fibula; tb. tibia; tb.fb. tibio- 

 fibulare ; tars. dist. distal tarsals. 

 (After Gegeiibaur.) 



