376 



Vertehrutu. 



another, as in the Siluroids, where the bases of well-developed rays may play 

 against the subjacent bones. 



The hearty which is situated anteriorly (see Fig. 285 A), is 

 usually almost bilaterally symmetrical. In Selachii, G-anoidei, 

 and Dipnoi, it consists of a large thin-walled auricle; of a 

 ventricle lying ventral to this, with thick walls of a spongy 

 nature, owing to the numerous offsets passing into them from the 

 small cavity; and lastly, of a tubular conus arteriosus, from 

 the anterior end of which the trunk of the branchial arteries arises, 

 and in which several rows of membranous watch-pocket valves are 



Fig. 310. Diagramraatio longitudinal section of the heart of different Fish. A of a 

 Pish with well-developed conns, B of Amia, of a Teleostean ; in B and the auricle is cut 

 away. a auricle, b bulbus arteriosus, which is only just indicated in Amia, c conus 

 arteriosus, fc valves, s sinus venosus, t cardiac aorta, v ventricle. — Orig. 



situated. All three sections are red, and their walls are furnished 

 with striated muscle-cells. In the Teleostei, the conus is, as a 

 rule, quite rudimentary (extremely short and without musculature), 

 and is provided with but two valves ; only in a few cases (from the 

 family of the Herrings) is it somewhat more significant, although still 

 very short ; and in a single genus [Butirinus) there are two rows 

 of valves.* In the Cyclostomes a conus is wanting. In Pisces there 

 is usually a transverse row of valves between the auricle and 

 ventricle, and between the sinus venosus {see below) and the auricle. 

 From the anterior end of the conus, or of the ventricle when the 

 former is absent, arises a longer or shorter cardiac aorta, which 



* In one of the Holostei, Amia, the conus is much shortened, and exhibits only three 

 rows of valves. 



