PELVIC ARCH 



111 



it is perforated by nerves, and gives rise on either side to an iliac 

 process (most marked in Holocephali) extending into the lateral 

 walls .of the body (Fig. 88). 



In all the above 

 cases we may look PP Cep 



upon the pelvic plate ; p^^i BP ; 



as essentially corres- 

 ponding, more or less 

 completely, with the 

 iscMo-'puhis of higher 

 forms. p^^_ 



Rad 



Fig. 8S. — Diagram of the Elas.mobeaxch Pelvis. 

 (From the ventral side. ) 



BP, Pelvic plate (ischio-pubis) ; I, iliac process ; 

 PP, prepubic process ; Cep, epipubic process , 

 Sy, region of the ischiopubic symphysis; Fo^. 

 obturator foramen ; Bas, Pro, Pad, basipterj'- 

 gium, propterygium, and radii of the fin. 



Dipnoi. — The 



small cartilaginous 



pelvic plate (Fig. 89) 



is provided with a 



long and delicate an- 

 terior median, a short 



posterior median, and 



two pairs of lateral 



processes. Of the 



latter the anterior 



(prepubic processes) vary much in form and length, being much 



longer in Protopterus than in Ceratodus, and each is embedded 



in an intermuscular septum ; 

 with the posterior the skeleton 

 of the free fin is articulated by 

 means of an intermediate piece. 

 The anterior unpaired process 

 must be looked upon as an 

 epipubic process, corresponding 

 with that of Amphibians, Rep- 

 tiles, and Mammals (pp. 113, 

 115, 121). 



Amphibia. — Urodela. — It 

 will be seen by a glance at 

 Fig. 87, D, that the ventral 

 portion of the pelvic arch of 

 Necturus is formed on the same 

 plan as the pelvic plate of the 

 Dipnoi and Crossopterygii, but, 

 as in all Urodela and Amniota, 

 it is perforated by the obturator 

 nerve : this indicates a further 

 lateral extension. Like the 

 pelvis of all Vertebrates, it has 

 a paired origin, and in Proteus 

 and Amphiuma this is indi- 

 cated by the fact that its 



ITE 



Fig. 89. — V'suviaov Protopterus. (From 

 the ventral side. ) 



a, prepubic process, which may become 

 forked at its distal end ; 6, process 

 to which the hinder extremit}' 

 (HE) is attached ; Gr, sharp ridge, 

 for attacliment of muscles ; o, epi- 

 bubic process ; ]\[, M, myotomes ; 

 M^, M^, intermuscular septa. 



