MM 



PHYLUM CHORDATA 



.S2.S 



cuds of the two bones being separated b\ a plate of calcified carti- 

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

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

 aperture in each pubis is the ohlmu dor foramen {Fo). A small rod 

 of bone, the os clodrcc, or hi/po-isckium (Ify. -^v), 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 rrii-^i, and the distal or ^jcs. The proximal division consists 

 of one bone, the femior ; the middle division of two, the tihicc and 

 fihukt ; the distal of the tarsal and metatarsal bones and the 

 pltalangcs. When the limb is extended at right angles with the 

 trunk, the tibia is pre-axial and the tibula 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 trwhanter, and a nearly 

 obsolete prominence on the post-axial side represents the greater 

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

 and external prominences or cundylea 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. D6G) comprises 

 only three bones in the adult, one 

 large proximal bone, the tibio-fibulare 

 (tb.fb), and two smaller distal {tars, 

 dist). Each digit consists of a meta- 

 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 Avith 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 {iwdatine teeth) on the palatine. On the floor of 'the mouth- 

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



tar.si/i.st 



Fig. 96fl.— Tarsus of Ziacerta agilis. 



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

 fibulare ; tarx. ili.-it. distal tarsals. 

 (After Gegeiibaur.) 



