362 FISHES. 



This muscular apparatus of their circulation * is composed of an 

 auricle («), of a ventricle (£), and of the bulb of the pulmonary 

 artery ( y ), and the auricle is preceded by a large sinus (S), in which 

 all the veins of the body terminate. This arrangement makes four 

 cavities separated by so many constrictions, which the blood must 

 successively pass through before it can get to the branchiae. The 

 whole of it is small in comparison to the size of the body, and does not 

 increase in the same ratio as the^ individual to which it belongs. 

 Three of these receptacles, the auricle, heart, and bulb are lodged in 

 the pericardium, which is, itself, placed beneath the pharyngean bones 

 and between the inferior parts of the branchial arches, and adheres 

 most commonly to the exterior by the humeral bones. Still its 

 position is varied, sometimes in the chondropterygians, and especially 

 in the lampreys. 



The great venous sinus (5) is not in the pericardium, but between 

 the posterior wall of their cavity, and the membrane which fills the 

 place of the diaphragm, and which is only the anterior part of the 

 peritoneum strengthened by aponeurotic fibres. 



This sinus is extended transversely, and receives by numerous 

 trunks the veins of the liver, the organs of generation (#), the 

 kidneys (<!>), the fins, branchiae, and neck, and lastly, the veins of the 

 head (a;), which themselves pass partly by a sinus (?) behind the cra- 

 nium. It sends, all the blood by a single orifice of its anterior con- 

 vexity into the auricle («), which is open at its posterior part to 

 receive it. Two thin membranous small valves are alone supplied to 

 this communication, as will be naturally conjectured, directed towards 

 the auricle. 



The auricle («) is in the pericardium anteriorly to the great ve- 

 nous sinus, and above the ventricle, or in other Avords, on the dorsal 

 surface. 



Its configuration is very varied and also quite fantastic ; it is in 

 general larger than the ventricle and overlaps it ; still its walls are 

 thinner, though they may be also of numerous fleshy columns. 



Its orifice pierced in its inferior surface is directed to the ventricle 

 (0), through the medium of the superior surface of the latter, and is 

 furnished with two small valves, which are analogous to the mitrals 

 of man, but their attachments are much more simple. 



The ventricle (#), at least in the osseous fishes, is generally in the 

 shape of a tetrahedron; sometimes it is oblong or very nearly oval ; 

 in the cartilaginous fishes its form is rounded, and frequently de- 

 pressed. 



It is below the auricle ; its cavity is turned round in such a way as 

 that being nearly vertical in the part which communicates with the 

 auricle, it becomes horizontal and longitudinal in order to terminate 

 at the bulb (7). Its walls are very vigorous and fortified on the 

 inside, with powerful, fleshy muscles ; its substance is formed of two 

 very distinct layers ; the internal has the fibres more transverse, in 



* The heat is seen in pi. 7, fig. I, laterally ; and from below, pi. 8, fig. I : 

 the sinus and auricle open above, pi. 8, fig, VIII ; the ventricle and bulb open 

 below, pi. 8, fig. VII. 



