Till ..;;... \X8 OF Till IMIKMKDIATK LAYER OR MB8KKCHTMK 



free edge is directed upwards and grows toward the bullniK arteriosus 

 anl ilf ttrioreatriealai opening. The latter originally lies men 



the left half of the \v: g .I In I gradually 



moves over moi-e to the right. and linally a-.umes such a pOM 



that the \entiiriilar paititloli l,y itSgfOWth npu ards meet* it OX > 



. 



Oi- 



I 



Fig. 310. Two diagrams to elucidate the change* in the mutual relation* of the 



ostium atrioventriculare and the ostiuin interventriculare, M well a* the division of the 

 ventricle and large arteries. 1 h<< \ .-utricles are imagined to have been divided into halve* 

 one looks into the posterior [dorsal] halves, in which, moreover, the cardiac trabeenls*. etc., 



i't-i'ii oiniur 1 for th- -akr nn the view. 



I, Heart of an embryo Rabbit, in which the head is 8-6-6-8 nun. leaf. The ventricle U 

 dividol i.y t ):,. vent .. a left and a right half as far a* theoetium 



iiiUTNi-ntriculare (Oi). The rijjht en.l >( t)..- : .:.men atrioveutriculare commune (F.ar.r) 



. endocardia! cushion* (e.tt. M.elr) are developed. 

 /.'. Heart of an embryo Rabbit, head 75 mm. long. The endocardial cushion* (o.tk. *.tk) of the 



.une are fused, and thereby the for airioventr. com 



separated into a for. atri. ' e.tl) and sinUtnim (F.or.i). The t 



I ..u t it ion (A-*) lias likewise fused with the endocardia! cushions, and ha* grown forward as far 

 n () of the truncu* arteriosua, By the closure of the remnant of the ostlam 



; septum membranaoeum is forced. 



rk, Riwhc. /M, arteria puImonalU ; Ao t aorta; 



arteriosns : uo ; f.m-.e, forarovn atrio- 



.men atrioventricnlare dextrum and ainislrmn 

 o.tk, u.ek, upper and lower endothclial or endocardia! cushiotu. 



in the mid. lie and roNfl \\ith its edges directly opposite the a 

 partition (li-,. ;jn'.i. :;h B). 



The divi>i..ii -Mtrirlrin M.i pleted as early a* 



seventh week I \vo compartments of \vlu.-h 



are united hy the tOi unen ovule, the blood in now - 

 a ri.irlit an.l a left o>tium ctnoventri -oparate4l 



ri^lil an-l left \entrirl.-. 



The two atriovei.trii-ulur openings are narrow at of 



: oiigin ; they are in pai i.med 



