4 8o 



ELEMENTARY ANATOMY. 



[LESS. 



Special respiratory structures may be added, as e.g. in the 

 climbing Perch (Anabas}, where the summits of the branchial 

 arches or epipharyngeal bones become enlarged and 

 curiously contorted to support an extension of vascular 

 mucous membrane. Again, in Saccobranchus and Amphi- 

 pnous, we find, by a very remarkable exception, a long 

 lung-like sac (with a highly vascular internal surface) 

 placed on each side of the body, and communicating with 

 the mouth by an aperture placed between the first branchial 

 arch and the hyoid. These organs receive blood from the 

 aortic vessels coming from the heart, and transmit it to the 

 dorsal aorta. 



There may be six or seven branchial sacs, as in the Sharks 

 Hexanchus and Heptanchus. On the contrary, not only may 

 the fifth branchial arch be devoid of a gill, as in all the Teleostei, 

 but even the fourth gill may disappear, and indeed only the 

 second gill may be left, as in Amphipnous. 



Sometimes, as in Lepidosteus and the Sharks, the hyoidean 

 arch also supports a gill. 



fuzz 



FIG. 406. 



The kidneys (A') ; ureters (Ur) ; with the aorta (Ao\ and vena cava inferior (VCI}\ 

 and the renal arteries and veins. Bl is the bladder, the top of which is cut 

 off so as to show the openings of the ureters (i, i) and that of the urethra (2). 



9. The general appearance, position, structure, and func- 

 tion of the KIDNEYS in man have been already noticed in 



