114 ME, W. G. EIDUWOOD ON THE HTOBEANCHIAL 



Witli regard to the arytenoid cartilages, authorities are all 

 agreed that they are the most anterior segments of the tracheal 

 skeleton : the point of dispute concerns the origiu of the latter. 

 E-ecent literature (Gegenbaur 15, Goppert 16, "Wilder 41 and 

 42) shows that there is a rapidly growing tendency to regard all 

 tracheal, bronchial, and arytenoid cartilages in Amphibia as pro- 

 ducts of the segmentation o£ a pair of elongated cartilages — 

 the fifth branchial arches — extending primarily along the right 

 and left sides of the trachea. The determination turns chiefly 

 upon the arrangement of these lateral cartilages in the lower 

 Urodela ; but it must not be forgotten that in these we are deal- 

 ing with long-bodied animals in which the length of trachea is 

 evidently correlated with that of the body : that is to say, that 

 the organ under consideration is not in its most primitive con- 

 dition. The subject is far too extensive to discuss in the limits 

 of these pages, but, in the case of Anura, there appears to me to 

 be far more to recommend the homology of the fifth branchial 

 arch of the fish with the thyrohyal than with the arytenoid and 

 cricoid cartilages. 



I regard the laryngeal cartilage of the frog as the perfect 

 equivalent of the cricoid cartilage of mammals, and I do not see 

 the force of Wilder's argument (43. p. 285) for calling it the 

 " aunulus ; " for, admitting that thyroid cartilages of whatever 

 form are secondary * hyobranchial derivatives, and that the 

 cricoid cartilage is formed by the modification of the first one or 

 more tracheal rings, there is sufficient difi'erentiation of laryngeal 

 structures here for all practical purposes. If the word " cricoid " 

 be employed in a strict sense, we should have to confine its 

 application to mammals, and to invent new names for the chief 

 laryngeal cartilage in other air-breathing vertebrates, according 

 to the amount of tracheal cartilage involved. 



"With the thyroid cartilage the case is different, and the term 

 must be employed more cautiously or hopeless confusion will 

 result. Gronberg, for instance, says with regard to the floor o£ 

 the larynx of Pipa (18. p. 635) : — " Wenn Dubois' Anschauung 

 richtig ist, dass die Cartilago thyreoidea bei den Saugethieren 

 aus dem 4, und 5. Visceralbogen nebst zugehoriger Copula 

 hervorgegangen ist, so konnen wir hier zum ersten Mai im 



* I use the word advisedly, in view of the prevailing custom, just cited, of re- 

 garding the whole of the respiratory cartilages as primary branchial derivatives. 



