VII 

 CIRCULATORY SYSTEM 



CIRCULATORY SYSTEM OF HEPTANCHUS MACULATUS 



The heart in Heptanchus (fig. 150) is located over, and in front of, the sternal 

 symphysis of the pectoral arch in the region between the gills, and is retained 

 within a relatively large pericardial cavity. It is made up of two rooms 

 proper, an auricle (atrium) (au.) and a ventricle (vn.), into the former of 



Fig. 150. A heart of Heptanchus macuJatus. (Marie Weldt, orig.) B. Valves of conus, ven- 

 tral view. (From Garman.) 



ap., aperture of last afferent artery; au., auricle (atrium) ; tr.af}''^, first and sixth bran- 

 chial afferent arteries; c.a., conus arteriosus; cr.l., left coronary artery; hy.af., hyoidean 

 aft'erent artery; p.c, pericardial; v.a., ventral aorta; v.c, valves of conus; vh., ventricle. 



which the blood enters from the sinus venosus (see p. 203, fig. 188, s.v.), and 

 from the latter of which it is expelled through the conus arteriosus {c.a., 

 fig. 150). 



The auricle, or atrium, is a greatly enlarged, thin-walled sac which lies dor- 

 sall,y over the ventricle. Connecting it with the sinus venosus is the sinu- 

 auricular opening. At the sides of this opening are the two sinu-auricular 

 valves (sa., fig. 188), which prevent the backward flow of the blood into the 

 sinus venosus upon the contraction of the auricle. Connecting the auricle with 

 the ventricle is an auriculoventricular opening guarded by valves of the same 

 name attached to the ventricular walls. 



The more or less triangular ventricle forces the blood by waj- of the conus 

 arteriosus through the gill capillaries and as a consequence of the strain 



[160] 



