92 



COMPAKATIVE ANATOMY. 



Pelvic Arch. 



Fishes. The Dipnoi have probably retained the most primi- 

 tive form of pelvis amongst existing animals. It consists of a 

 cartilaginous plate lying in the mid-ventral line, from which two 

 pairs of processes, an anterior and posterior, arise. The hinder 

 extremities articulate with the posterior (Fig. 76, I), while the 

 anterior pair are to be interpreted as iliac processes (Fig. 76, a). 

 The latter vary much both in form and size, and, as in young 

 specimens of Protopterus, may extend widely outwards, embedded 

 in the intermuscular septa (J/ 1 ). A delicate rod-like process 



FIG. 76. PELVIS OF Protopterus. (From the ventral side. ) 



a, iliac process, which may become forked at its distal end ; b, process to which the 

 hinder extremity (HE) is attached ; Gr, sharp ridge, for attachment of muscles ; 

 c, median process ; M, M, myotome.3 ; M l t M l , intermuscular septa. 



arises between them from the anterior border of the plate and 

 extends far forwards in the middle line (Fig. 76, c). 



The pelvis of Elasrnobranchs may be derived from that of 

 Dipnoi, although it must be looked upon as a degenerate form. 

 It consists of an unpaired or paired plate of cartilage, on which 

 processes corresponding to those described in Dipnoi may be seen, 

 though these are often very rudimentary. In Chimsera an iliac 

 tract is much more plainly marked. 



Amongst all other Fishes, the existence of a pelvic rudiment 

 has been proved with certainty only in the case of Polypterus. 



Amphibia. In Amphibia, as in all the remaining higher 

 Vertebrata, a dorsal and two ventral pelvic elements may be 

 distinguished. The former, or ilium, is connected with the sacral 



