294 H, H. WILDER, 



Part II. Muscles. 



1. The respiratory muscles of I^ecturus. 



As in the case of the cartilages, we must take the Proteidae as 

 the point of departure for the respiratory muscles, believing that 

 these forms, though variously modified, still preserve many of the 

 characteristics of the fish-like ancestors of air-breathing Vertebrates. 



As we have traced the laryngeal cartilages to branchial elements, 

 we must expect the larynx to be supplied by gill-musculature, and 

 this is still recognizable here. By a singular chance, the branchial 

 system is here rendered incomplete by the failure of the 4tii epi- 

 branchial, present in many of the higher forms, but as its position is 

 still represented by a tendinous inscription, as recently shown by 

 GöPPERT (No. 6), this lack is an unimportant one. 



We may take, then, the conditions found in Necturus as the 

 most primitive now left us, and thus this animal may serve us as a 

 key to the morphology of the system, from which we may deduce a 

 primitive and generalized type to serve as a basis for terminology. 



Any description of the pharyngeal and laryngeal muscles of 

 Necturus which does not include the Levatores arcuum would be 

 incomplete, and in order to bring these out in connection with the 

 other parts under discussion, the head must be removed and the ex- 

 posure made of the pharyngeal and lateral gill regions. This may 

 be accomi)lished either by splitting the head in the median plane and 

 drawing the parts aside, as recommended by Göppert (No. 6), or by 

 cutting through one side, beginning at the angle of the mouth and 

 folding the head over upon the other side. This latter method, al- 

 though giving an exposure of one side alone, furnishes a better 

 opportunity for tracing the Levatores arcuum to their origin, and 

 completely exhibiting their relation to the other parts, for, after 

 making the exposure of the i)haryngeal muscles, the entire head may 

 be dissected away, leaving only the integument for the purpose of 

 showing muscular origins. Such a dissection will present the aspect 

 shown in Fig, 8. The floor of the pharyngeal cavity is seen to be 

 covered by a sheet of muscle, disposed in bundles corresponding to 

 the branchial arches, and divided by them into dorsal and ventral 

 portions. Thus the 2»^ branchial arch possesses a dorsal, but no 



