HEART OF FISHES. 



471 



310 



separate branchial arteries of the Cephalopoda. 1 In other species 

 of Bdettostoma the artery extends beyond two or three pairs of 

 gills before it bifurcates; and Miiller 2 saw one instance in the 

 Mijxine glutinosa, where the branchial artery 

 continued single as far as the anterior gills. 



The pericardium of the Ammocete com- 

 municates by one wide orifice with the peri- 

 toneum : that of the Lamprey is a shut sac, 

 and is supported by a perforated case of 

 cartilage, formed by the last modified pair of 

 branchial arches, fig. 310, m. Not any of the 

 Dermopteri possess the < bulbus arteriosus : ' 

 this is present, and forms, as it were, a 

 third compartment of the heart, 311, B, 

 beyond the ventricle, ib. A, and auricle, ib. 

 C, in all other Fishes : nay, if we include 

 the great ( sinus communis,' ib. D, as part of 

 the heart, then we may reckon four cham- 

 bers in that of Fishes; but these succeed L - 

 each other in a linear series, like the centres 

 of the brain, and their valves are so disposed 

 as to impress one course upon the same cur- 

 rent of blood from behind forward, driving 

 it exclusively into the branchial artery and 

 its ramifications. This is very different 

 from the arrangement and relations of the 

 four compartments of the human heart. 

 Physiologically the heart of Fishes answers 

 to the venous or pulmonary division, viz. 

 the rischt auricle and ventricle of the mammalian heart, and 



O ' 



its quadripartite structure in Fishes illustrates the law of vege- 

 tative repetition, rather than that of true physiological compli- 

 cation. The auricle and the ventricle are, however, alone proper 

 to the heart itself: the sinus is a developement of the termination 

 of the venous system, as the muscular bulb is a superaddition to 

 the commencement of the arterial trunk. The heart of Fishes 

 with the muscular branchial artery is the ' homologue ' of the left 

 auricle, ventricle, and aorta in higher Vertebrates ; but it performs 

 a function ( analogous ' to that of the pulnionic auricle and ventricle 

 in them. 



Some of the higher organised Fishes, which present the normal 

 structure of the heart, have, like the Myxinoids, a perforated 



Heart and gills, Lamprey 

 (Petromyzon). cxx. 



1 xx. vol. ii. p. 78, prep. no. 1018. 



xxi. p. 9. 



