-MOKPHOLOiiY OF CIJANIAL MUSCLES IN SOME VEliTEB KATES. 241 



third arch; tins, on comparison with the interarcualis ventralis 

 IV of Amia, is probably an iuterarcualis ventralis III, which 

 lias additionally extended back to the fourth bar. In front 

 of this are the interarcuales ventrales II and I, the former 

 pnssing from the second to the first cerato-branchial, and the 

 latter from the cerato-braucliial to the ceratohyal (Text-figs. 

 oo and 06). 



In Polypterus senegalus there are transversi ventrales 

 III and IV (Text-figs. 06, 37); the median edges of the 

 former are attached to the basiljranchial ; the latter in its 

 anterior part forms a transverse muscle, and in its posterior 

 part enters into relation with the rima glottidis, forming the 

 dilatator of Wiedersheim. He called the fore part of the 

 muscle M. adductor arc. branch., but adductors, in the sense 

 of Vetter, are not present in Polypterus senegalus, and 

 the whole nniscle is a transversus ventralis of the fourth arch. 



In Polypterus, ? species, Pollard described four "inter- 

 arcuales ventrales " (i.e. in the terminology of this paper, 

 " obliqui ventrales"), one to each branchial bar. In Poly- 

 pterus senegalus these muscles are not present in the first 

 and second branchial segments ; in the third and fourth 

 segments their dorsal portions are present in the form of very 

 minute muscles, the lower ends of which are attached to the 

 cerato-branchiales (Text-fig. 37). l^ollard described four leva- 

 tores arcuum branchialium inserted into the upper ends of the 

 cerato-branchials. In Polypterus senegalus the first is 

 inserted into the first pharyngo- and epi-branchial, the second 

 and third into the respective pharyngo-brauchials, and the 

 fourth, which has an additional head from the third pharyngo- 

 branchial, into the fourth cerato-branchial. According to 

 Pollard, thei'e is no trapezius corresponding to that of 

 Selachians, but he mentions that a muscular slip — presumably 

 of the fourth levator — continues on beyond the last (fourth) 

 cerato-branchial, and is inserted into the skin-ligaments in 

 front of the shoulder-girdle. In Polypterus senegalus 

 there is a trapezius arising in common with the fourth 

 levator and passing back to the shoulder-girdle (Text-fig. 37), 



