of the Anatomy of the Squalus Maximus. t^ 



an inch long, rising from the edge of the opening of the 

 ventricle which projects into the artery.* 



These different structures, so very unlike one another, and 

 bearing no resemblance to the mechanism of the same parts 

 in quadrupeds, make it probable, that the circulation through 

 the gills is impeded by the external pressure of the water, 

 in different degrees according to the depth of the fish from 

 the surface: therefore in those fishes which frequent great 

 depths, as the Squalus Maximus and all the shark tribe, there 

 is a muscular structure in the coats of the branchial artery, 

 which, when the fish is deep in the water, by its contraction 

 diminishes the area of the vessel, and makes the valves per- 

 form their oflfice ; but when the fish is near the surface, this 

 muscular structure, by its relaxation, renders the area of the 

 artery so wide, that regurgitation of the blood takes place into 

 the ventricle, and prevents the small vessels of the gills from 

 being too much loaded. -j^ 



In fishes that swim deep, and do not come to the surface, 

 as the wolf fish, the regurgitation does not take place into the 

 ventricle ; but the relaxation of this muscular portion of the 

 artery allows it to dilate, and form a reservoir, and the valves 

 remain closed, so as to prevent more blood leaving the ven- 

 tricle. In fishes residing at moderate depths, as the turbot, 

 elasticity is employed as a substitute for muscular power, there 

 being less variation in the pressure made upon the gills ; but in 

 the Lophius Piscatorius, which probably never descends into 



* This structure, which it is difficult to describe, will be better understood by a 

 reference to the annexed drawing. (PI. XXII.) 



f That such regurgitation takes place when the muscle is relaxed, is ascertained 

 by the ventricle being readily injected after death with common wax injection from the 

 artery, the valves allowing it to pass. 



MDCCCXIII. I i 



