526 



ANATOMY or VEKTEBRATES. 



are the largest and tlieir 



along the outer margin of the lung 

 parietes the least vascular. 



Subjoined is a tabular view ' of the capacity of the lungs in 

 examples of different families of the Chelonian order, ' obtained 

 by pumping out the air of the lungs, then pumping in water, 

 then pumping out the water again and measuring its amount in 

 cubic inches.' ^ This table shows that aquatic Chelonia require 

 less air in their lungs, in proportion to the weight of the body, 

 than land Chelonia ; and that in mud-dwellers and the soft-turtles 

 ( Trionycida) other parts are auxiliary to the lungs in the act of 

 breathing. Thus the more permeable texture and minor thick- 

 ness of the epiderm in the Trionycidm suggest the aptness of the 

 skin for respiratory influence on the blood, analogous to that of a 

 gill. The integument of the under side of the body in these 

 estuary turtles, which seldom leave the water except to lay their 

 eggs, is highly vascular. 



Dr. Sager found ' arranged along the surface of the tongue of 

 Trionyx, and somewhat in rows, as well as on the fauces and 

 about the rima glottidis, and also over the edges of the cornua 

 hyoidea, a number of delicate fringes, resembling, especially on 

 the hyoid arches, the fimbriated gills of the Menobranchus.' ^ 

 Professor Agassiz remarks that, ' after seeing this Turtle remain- 

 ing under water for half-an-hour without showing the least sign 

 of oppression, it seems plausible to assume that these fringes may 

 be similar to the internal gills of Tadpoles, not only in their 

 shape but also in their function.' '' 



In the Crocodile ( Crocodilus acutus) the bronchial tube enters 

 the middle of the lung and is continvied for a short distance into 

 its substance before losing the cartilaginous annular structure, 



TABLE SUOWINO THE CAPACITY OF THE LUNGS COMPARED TVITH THE TVEICnT 

 OF THE BODY. CCC. p. 283. 



CCC. vol. i. p. 284. '' cccii. quoted in ccc. pp. 277, 284. 



' Iliid. p. 284. 



