VI 



HEART OF BIRDS 



385 



left ventricle. This division comes about in ar somewhat 

 fashion thti chid' points in which, judging from Greil and li 

 stetter's descriptions and (inures, appear to be as follows. The 

 ventricular portion of 1 he cardiac tube is at an early stage encroached 

 upon by the deep (" bullio-auricular ") fold which separates the conus 



ats. 



rcc 



E. 



D 



Fi.;. IS:!. -Stages in the development of the tisart of the Fowl, viewed from the right 

 side. The ri^ht wall of the heart has been removed in each case. (After original 

 drawings by Greil.) 



.1. /.'. proximal emls of ridges of conns; "'.-, at rial septum ; b.a.r, bulboaurieular ridite : , conns 

 arteriosus ; /./-./. intei ventricular foramen; i.V., tralterular portion of ventrieular septum; /.<, left 

 auricle; /, pulmonary artery : /.". ri-ht auricle; /...<, cut. surface of endocanliae tissue of atrio- 

 venti icularoiienin- ; / . I', ca\ ity ofri.^ht vent rielr ; s, systemic aorta : !', venlriele ; 1. _', ;!, conu- 



from the atrial part of the heart (Fig. 182, A, b.a.f). The encroach- 

 ment of this fold gives the ventricular part of the tube a squat 

 U -shape. As the ventricle dilates the extent of the encroachment 

 becomes reduced and the fold may now be called the Imlbo-auricular 

 ridge of the heart-lining (Fig. 183, A, b.a.r). During the fourth 

 day this becomes extended tailwards along the ventral wall of the 



VOL. II 2 C 



