HEART 



249 



from the air-bladder, passes right through the sinus venosus to 

 the left side of the atrium, and discharges the arterial blood 

 almost straight into the ventricle. This incipient division of 



y 



PIG. -218. 



Heart of Protopterus annectens, Owen. A, dorsal view. 13, opened, ventral view. C, the 

 sinus venosus opened, a, cut arterial arches ; 1 and 2, entrance from conns to first two 

 arches ; a 3 and 4, entrance to last two arches ; at, atrium ; c, con us arteriosus ; c.w.c, cut wall 

 ofconus; c.w.v, cut wall of ventricle ; /, fibrous plug closing the passage from ventricle to 

 .atrium and passing into the sinus ; I, dorsal attachment to pericardial wall ; /.', left dnctus 

 Cuvieri ; Iv, longitudinal ridge ; p, small portion of pericardial wall ; p.r, pulmonary vein ; /-.</, 

 right ductus Cuvieri ; sv, longitudinal compound valve ; v, ventricle ; v.c, vena c-ava inferior ; 

 vv, row of small valves ; w, dotted line indicating course of venous blood from the shallow 

 sinus venosus, through the atrium (C) into the ventricle on the right of the ping (B). In C the 

 dotted lines Id, rd, and vc pass into the sinus venosus ; the lines .r and y into the cavity of the 

 Atrium opening widely into the sinus ; the line p. v passes down the pulmonary vein to outer 

 the ventricle on the left of the plug (Z in B). 



the heart into a venous and an arterial channel is continued in the 

 atrium, where an incomplete interauricular wall is developed as a 

 thick projecting plug, and is even carried on into the ventricle. Of 

 the four main longitudinal rows of valves found in the spirally 



