DEVELOPMENT OF THE CIRCULATORY SYSTEM. 



239 



2. The Inter- ventricular septum. 



3. The Aortic septa. 



4. The septum primum of the auricle. 



5. The septum secundum of the auricle. 



(1) The auricular or auriculo-ventricular canal is divided by 

 anterior and posterior endocardial cushions, which grow out and 

 meet, dividing the auricular canal into the right and left auriculo- 

 ventricular orifices. 



(2) The inter-ventricular septum rises from the floor of the 

 common ventricle and grows upwards towards the aortic orifice 

 and endocardial cushions (Figs. 197 and 198). 



(3) In the aortic bulb (Fig. 198) appear anterior and posterior 

 aortic ridges, arranged spirally. They fuse together ; their lower 

 extremities unite with the inter-ventricular septum. The conus 



aorta 



aortic sept. 

 aortic sept, 

 t. endocard. cushion 

 pars memb. septi. 

 interuent. sept. 



upper edge of 

 sept. prim. 



sept. sec. 



sept. prim. 



for. ovale t 



left, 

 ven. value 



cor. sin. 



inf. ven. cav. 



auric' ~ ~"" '^post. endocard. cushion 

 Eustach. or right ven. valve 



Fig. 19S.-Diagram of the Septa of the Heart viewed on the right side. 



or bulbus arteriosus is thus divided into an anterior or pulmonary 

 part connected with the right ventricle, and a posterior or aortic 

 part connected with the left ventricle. 



Pars Menfbranacea Septi.— The three septa just described meet 



