260 



THE FIFTH DAY. 



[chap. 



nearly backwards {i. e. towards the tail), but also a little 

 ventralwards. 



An alteration takes place during the sixth day in 

 the relative position of the parts of the ventricular 

 division of the heart. The right ventricle is now turned 

 towards the abdominal surface, and also winds to a 

 certain extent round the left ventricle. It will be 

 remembered that on the fourth day the right ventricle 

 was placed dorsal to the left. 



The right ventricle is now also the smaller of the 

 two, and the constriction which divides it from the left 

 ventricle does not extend to the apex of the heart 

 (Fig. 84). It has, however, a very marked bulge to- 



wards the right. 



Fig. 84. 



B 



r.y 



Two Views of the Heart of a Chick upon the Fifth 



Day of Incubation. 



A. from the ventral, B. from the dorsal side. 



l.a. lefb auricular appendage, r.a. right auricular appendage. 

 r.v. right ventricle, l.v. left ventricle, b. bulbus arteriosus. 



At first the bulbus arteriosus appeared to come off 

 chiefly from the left ventricle ; during the fifth day, and 

 still more on the sixth, it appears to come from the 



