88 SUPPLEMENT ON 



alone being provided at its basis with a muscular apparatus, 

 a heart corresponding to the auricle and right ventricle of the 

 other class of animals just mentioned, and that they have 

 nothing similar at the basis of the circulation of the body; 

 in other words, that here they are entirely deprived of an 

 organ to represent the left auricle and ventricle, their 

 branchial veins changing into arteries without a muscular 

 inclosure. 



The muscular apparatus of their circulation is composed of 

 the auricle, the ventricle, and of the bulb of the pulmonary 

 artery, the auricle being preceded also by a large sinus where 

 all the veins of the body terminate ; thus four cavities sepa- 

 rated by contractions are successively traversed by the blood 

 in passing from the body to the branchiae. Their size is 

 inconsiderable when compared with the bulk of the body, 

 and does not increase in the same ratio with the growth of 

 the animal. Three of these receptacles, the auricle, the 

 heart, and the bulb, are lodged within the pericardium, 

 which is itself situated below the pharyngeal bones, between 

 the inferior parts of the branchial arches, and externally pro- 

 tected by the humeral bones. The great venous sinus is not 

 placed within the pericardium, but between the external 

 membrane of that cavity, and the membrane which represents 

 the diaphragm. This sinus lying transversely, receives by 

 different trunks the veins of the liver, of the organs of gene- 

 ration, the kidneys, the fins, the branchise and throat, and 

 finally, those of the head ; which last partly pass themselves 

 through a sinus at the back of the cranium. The whole of 

 the blood thus collected in the sinus passes, by a single ori- 

 fice in its anterior convexity, into the posterior part of the 

 auricle, where there are for this purpose two membranous 

 valvulee opening towards the auricle. This organ, placed be- 

 fore the great sinus, and within the pericardium, is above the 

 ventricle that is against its dorsal surface, and presents very 



