VASCULAR SYSTEM. 



285 



in which the longitudinal valve of the conus and the horizontal septum 

 of the ventral aorta are less developed, no separation of the arterial (pul- 

 monary) blood from the systemic venous blood is possible ; the two must 

 undergo complete admixture in passing through the ventricle, conus 

 and ventral aorta. In the Anvra however this is not the case. In these 

 animals the anatomical arrangements are of a nature to ensure that the 

 pulmonary arteries receive purely venous blood, the mixed and purely 

 arterial blood being directed into the aortae and the carotids. It is further 

 said that the carotids receive more purely arterial blood than the systemic 



M+IV-1. 



FIG. 159. Conus and ventral aorta of Eana plaiyrrhina, opened along the ventral side 

 ventral aorta slightly diagrammatic (after Boas). 7, 77, III IV roots of the aortic 

 arches, carotid, aortic, and pulmonary (777 7 V] ; p p bristle inserted from the conus 

 into orifice of the pulmonary, it passes dorsal to the horizontal septum of the ventral aorta 

 through the opening guarded by valve So. 2 and Ib ; 2 valve No. 2 of anterior row ; 3 valve 

 No. 3 of anterior row ; la ventral half of valve No. 1 which with 3 guards the entrance into 

 the ventral division of the ventral aorta which has been laid open ; the other half of this 

 valve 16 is not shown : the attachment of la to the left hand wall of the conus is between 

 valve 2 and 3 ; this is not clearly shown in the figure ; co conus ; sp longitudinal (spiral) 

 valve of conus ; tr ventral aorta (points a little too far up). The hind end of the conu* 

 where the attachment of the longitudinal valve becomes ventral is not shown. 



aortae ; this may be true, but it is not quite so clear from the arrangements 

 how it is effected. 



The ventricular cavity is, except at its base where the auricles and 

 conus open, broken up by muscular bands so as to assume a spongy 

 character. This prevents the mixture of venous and arterial blood which 

 is poured in from the auricles. The blood which enters from the right 

 auricle is venous, and this is discharged into the right side of the ventricle 

 from which the conus arises ; consequently the blood which flows into 

 the conus during the first phases of the ventricular systole will be venous. 

 This will distend the conus and fill both chambers into which it is im- 

 perfectly divided by the longitudinal valve, and passing forward along the 

 cavum pulmo-cutaneum will also fill the pulmonary arteries which are- 



