PARTS OF THE HEART. 329 



left heart. The term liemicardia is analogous with the words hemi- 

 sphere, hemipteron, etc. The left auricle and ventricle constitute 

 the hemicardia sinistra. 



Hemiseptum auriculare and hemiseptum ventriculare. Not 

 only ideally, as in Fig. 92, but actually may the inter-ventricular 

 septum be divided so that a portion remains as the mesal wall of 

 either ventricle. Strictly speaking, each of these parts is not a sep- 

 tum, but a hemiseptum, but practically the latter term need seldom 

 be employed. 



870. Orificiuxn auriculo- ventriculare dextrum, orf. aur.-vnt. 

 dxt.The right auriculo-ventricular orifice (Fig. 92, 93, 96, 97, 99). 

 This is the slightly constricted communication between the right 

 auricle and ventricle. It is guarded by the tricuspid valves. 



The similar orifice between the left auricle and ventricle is 

 guarded by the bicuspid valves. 



871. Postcava (az.),pcv. The posterior or caudal vena cava 

 or V. cava inferior s. ascendens (Fig. 91, 92, 95, 101, 955). This 

 large vein enters the right auricular sinus on its dorsal aspect near 

 the ventricle. Respecting the name, see 886. 



872. Praecava (az.\ prcv. The anterior or cephalic vena cava 

 or V. cava superior s. descendens (Fig. 91, 92, 93, 95, 101, 919). 

 This opens into the right auricular sinus at its cephalic aspect, 

 just dorsad of the arch of the A. pulmonalis. 



873. Septum auriculare (az.\ spt. aur. The partition be- 

 tween the right and left auricles (Fig. 93, 95, 96, 99). This is hardly 

 thicker than the lateral auricular wall and is very thin at the fossa 

 ovalis. In Fig. 93, what is named septum embraces also the mass 

 of connective tissue between the aorta and the bifurcation of the 

 septum proper as seen in Fig. 96. The septum is really between 

 only those larger portions of the auricles known as the sinuses. 



874. Septum ventriculare (az.), spt. wit. The partition be- 

 tween the right and left ventricles (Fig. 93, 97, 98). The septum is 

 about as thick as the lateral wall of the left ventricle. 



875. Sinus (auriculae dextrae), sn. aur. dxt. The sinus or 

 larger and more dorsal portion of the right auricle (Fig. 91-96). 

 Its walls are smoother within than those of the appendix. Into it 

 open the postcaoa, the prcecava and the V. cardiaca. 



876. Sinus (auriculae sinistrae), sn. aur. sin. The left auricu- 

 lar sinus (Fig. 91, 92, 93, 95, 96). The larger and more dorsally 



