312 HISTORY OF THE HUMAN BODY 



emancipated from all respiratory function, and employed in a 

 desultory way as tooth-bearing structures or as parts assisting 

 in deglutition, were lying in the immediate neighborhood, one 

 on each side of the glottis but a little anterior to it, and 

 equipped with well-differentiated muscles ; and it may well have 

 happened that little by little these parts may have usurped the 

 function of the other apparatus, being better fitted for the 

 purpose. 



Be that as it may, when, after a succession of forms that 

 have become lost, the curtain rises upon the lowest of the 

 amphibians, this very pair of arches is seen lying, one upon 

 each side of the glottis, and forming with its muscles a primi- 

 tive though very effective larynx. These cartilages are 

 proven to be the actual 5th pair of gill-arches through the iden- 

 tity of their nerve supply, and the weak point in the story is the 

 identity of the two pulmonary systems, that of the ganoid and 

 the definite one found in terrestrial vertebrates, a point not yet 

 proven; but, granting this, a theory which seems extremely 

 probable, the rest must follow. In all events the history of 

 both lungs and larynx from the amphibians on is a continuous 

 one, and the latter organ, equipped at the start with the $th 

 branchial cartilages and their associated parts, becomes more 

 complex by the gradual addition of other arches, proceeding 

 from behind forwards, each accommodating itself in shape 

 and position to the especial function desired in each case. 



The simplest amphibian larynx is that of the perenni- 

 branchiate salamander Necturus, where the two cartilages 

 in question are in the form of flattened triangular pieces, the 

 lateral cartilages, placed one upon each side of the glottis 

 (Fig. 87, a). A short membranous trachea, entirely without 

 cartilaginous support, leads to the bag-like lungs. In an 

 allied form, Proteus (Fig. 87, b), a slight advance is seen in 

 the fact that the posterior angles of the lateral cartilages are 

 more prolonged and appear as slender processes which are 

 applied along the sides of the entire trachea as far as the 

 bronchi. These in adult animals show a tendency to separate 

 from the main mass. This differentiates the cartilaginous 



