PARTS OF THE HEART. 329 



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

 spJiere, Jiemipteron, etc. The left auricle and ventricle constitute 

 the hemicaxdia sinistra. 



Hemiseptum auriculare and hemiseptum ventriculare. — jN"ot 

 only ideally, as in Fig. 92, but actually may the interventricular 

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

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

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

 be employed. 



§ 870. Orificium auriculo-ventriculare dextrum, ot/. aur.-vnt. 

 dxt.—l^hQ right auriculo-ventricular orifice (Pig. 93, 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.\p&o. — The posterior or caudal vena cava 

 or Y. cava inferior s. ascendens (Pig. 91, 93, 95, 101, § 955). — This 

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

 the ventricle. Eespecting the name, see § 886. 



§ 872. Prsecava {az.\ prcv. — The anterior or cephalic vena cava 

 or y. cava superior s. descendens (Pig. 91, 93, 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- 

 tweeii the right and left auricles (Pig. 93, 95, 96, 99). — This is hardly 

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

 malis. In Pig. 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 Pig. 96. The septum is really between 

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



§ 874. Septum ventriculare {az.), spt. 7mt. — 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 dextrse), sn. aur. dxt.—Tha 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 Vae postcava, the prcecava and the V. cardiaca. 



§ 876. Sinus (auriculse sinistrse), sn. aur. sin. — The left auricu- 

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



