420 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



/ 



muscles of the trabecular Processes from the connective tissue layer 

 pass in among the muscles of the wall, and, uniting again, form an 

 inner layer to which the muscles of the trabecular are attached. The 

 fasciculi of the latter resemble those of the atrium, but are placed 

 more closely together. Their arrangement leaves a central cavity 

 which extends from behind the atro-vencricular opening to the bul- 

 bils, and many smaller spaces as well. The surface of the ventricle 

 is smooth, and between the two sets of muscles there are no lymph- 

 spaces as described by Kasem-Beck and J. Dogiel 1 in their investiga- 

 tions on the heart of Esox and Acipenser. There are large spaces in 

 the inner connective tissue layer toward the apex, opposite the ostium 

 atro-ventriculare, but they are blood-cavities connected with the 

 other spaces of the venti'icle. While I have not attempted to demon- 

 strate the endothelial layers described by the above-mentioned inves- 

 tigators, I doubt the existence of the inner one in Amiurus, for at 

 points the muscle-fibres of the one layer pass into the other as do also 

 the connective tissue fibres, except at the spaces. In comparing the 

 structure of the ventricle with that of the atrium the only difference 

 is that the former has a dense muscular layer without blood-spaces 

 developed between the connective tissue layer and the trabecules carn<z, 

 which greatly strengthens the wall. The heart of such fishes as are 

 supposed to possess double walls should be further studied, and 

 especially its development. 



The base of the bulbus is provided with a narrow neck which is 

 inserted into the central cavity of the ventricle to which it is attached 

 by its outer surface. At this opening a pair of valves is attached 

 to the muscles of the ventricle similar to those attached to the atrium. 

 Their extremities, however, extend forward as ridges upon the wall 

 of the bulbus to strengthen them. Curving upward the bulbus 

 passes into the truncus arteriosus, which runs almost at right angles 

 to the axis of the ventricle. 



The walls of the bulbus, ventricle and atrium are well supplied with 

 blood-vessels. An artery passes along the dorsal surface of the bul- 

 bus to the ventricle; where it divides in two stems which distribute 

 themselves on each lateral surface. Another artery runs along the 

 ventral surface of the bulbus and ventricle and gives off a branch on 

 the former to the dorsal surface of the latter. The veins pass back- 



i Beitrag zurKennt. cl. Structur u. Function d. Herzend. Knochen-flscbe, Zeit. fiir wiss. Zoo 

 Vol. XXXVII., p. 247. 



