xin PHYLUM CHORDATA 323 



ends of the two bones being separated by a plate of calcified carti- 

 lage. Between the pubes and ischia is a wide space divided by a 

 median ligament (Ig) into a pair of apertures, and a smaller 

 aperture in each pubis is the obturator foramen (Fo'}. A small rod 

 of bone, the os cloacae, or hypo-isekium (Up. Is), passes backwards 

 from the ischiatic 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 cms, and the distal or pes. The proximal division consists 

 of one bone, the femur ; the middle division of two, the tibia and 

 fibula; the distal of the tarsal and metatarsal 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 troehanter, and a nearly 

 obsolete prominence on the post-axial side represents the greater 

 trochanler. The distal extremity is pulley-shaped, with internal 

 and external prominences or condyles for articulation with the 

 tibia ; immediately 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 extremity pre- 

 sents two articular surfaces for the 

 condyles of the femur. The fibula 

 is a slender bone, the proximal end 

 articulating with the external tuber- 

 osity of the femur, the distal with 

 the tarsus. 



The tarsus (Fig. 966) comprises 

 only three bones in the adult, one 

 large proximal bone, the tiUo-fibv,lare FlG . 9 66.-Tarsus of Lacerta agiiis. 

 (tb.fb\ arid two smaller distal (tars. /? , fibula ; tb - bia j A . tb -{ b - iib \- 



... . fibulave ; tars. dist. distal tarsals. 



dlSt). Each digit Consists Of a meta- (After Gegenbaur.) 



tarsal bone and phalanges, the 



number of the latter being respectively two, three, four, five, and 

 three. The first and second metatarsals articulate with the tibial 

 side of the tibio-fibulare, the rest with the distal tarsals. 



Digestive System. The upper and lower jaws, forming the 

 boundary of the aperture of the mouth, are each provided with a 

 single row of small conical teeth, and there is a patch of similar 

 teeth (palatine teeth] on the palatine. On the floor of the mouth- 

 cavity is the tongue, a narrow elongated fleshy organ, bifid in front. 



