274 THE SALAMANDER 



action. It is possibly related to the new development of the dilatator laryngis 



in Amphibia. The tracheal skeleton s. pars trachealis cartilaginis lateralis is 



a backward prolongation of the arytenoid and related to the development of the 



trachea. 



It must be noticed that an excellent description of both the 

 muscles and the skeleton of the larynx of Salamandra was given as 

 early as 1 839 by Henle, but he made no suggestions as to the homo- 

 logies of the several parts. 



Physiological Considerations. 



It is well known that the common Frog is capable of respiring to 

 a large extent through the skin as well as through the lungs. That 

 Caducibranchiate Urodeles are also not entirely dependent on pul- 

 monary respiration is obvious from the fact that many are devoid of 

 lungs altogether, e.g. Eurycea (Spelerpes), Salamandrina, &c., while 

 the lungs of other forms, e.g. Triton, are mere hollow sacs with 

 smooth walls which present only a relatively small surface to the 

 contained air, and are probably hydrostatic rather than respiratory 

 in function. In support of this latter statement Lonnberg (1899) 

 points out that all aquatic Urodeles devoid of lungs craw/ r^ither than 

 swim. Numerous experiments have been carried out, by Camerano 

 and others, with the object of discovering to what extent the skin 

 acts as a respiratory medium. These have been well summarized by 

 Bethge (1898), and it is not proposed to discuss them here. They 

 are none of them free from the objection that they do not ensure the 

 absence of secondary effects being introduced which may affect the 

 general health of the animals being treated. Bethge himself draws 

 attention to the interesting fact that the cutaneous capillaries of 

 Salamandra — where the lungs have an undoubted respiratory func- 

 tion — have only about one-half the diameter of those of Eurycea 

 (Spelerpes), an animal entirely devoid of lungs, while in Triton — 

 whose lungs are largely hydrostatic in function — the capillaries of 

 the skin are about intermediate between the other two. It therefore 

 seems probable that the skin has some influence in respiration but 

 only to a slight extent in Salamandra. 



In 1906 Whipple made a careful study of the respiratory move- 

 ments of pulmonate Urodeles, and, while she did not use Salamandra 

 itself, her conclusions are quite applicable to that animal. She finds 

 that there are two forms of respiratory movements in Urodeles 

 possessing lungs. The first consists of a shallow oscillation of the 

 floor of the mouth which takes place rapidly and continuously, and 



