152 



FISHES. 



is a swelling of the artery, without muscular stratum and with- 

 out contractility ; with the exception of the Myxinoids its walls 

 are thick, fibrous, with many trabeculse and pouches, but it 

 has no valves in its interior, and is separated from the ven- 

 tricle by two valves ojDposite to each other. This Teleostean 

 type is called hulbus aorta. 



The sinus venosus sends the wdiole of the venous blood 

 by a single orifice of its anterior convexity into the atrium ; 



Fig. 68. — Bulbus aortae of Xiphias gladius, opened. 

 a, Section tlirougli part of the wall of ventricle ; h, Section through the bnlbus ; 

 c, Teleosteous valves of the ostium arteriosum ; d, Accessory valves, of rudi- 

 mentary nature and inconstant ; e, Trabeculae carnese of the bulbus. 



two thin membranous valvules turned towards the atrium, 

 prevent the blood from re-entering the sinus. A pair of other 

 valves between atrium and ventricle have the same function. 

 The walls of the ventricle are robust, and, internally, it is 

 furnished with powerful fleshy trabeculae. 



