1861 ] DR. A. GUNTHKR ON THB ANATOMY OF MONITOR. Ill 



vena cava superior externa is diagonally o])posed to that from the v. 

 cava inferior, and that the current from the v. cava superior interna 

 coming from the left is at right angles with the concurrence of the 

 •former. 



a. Vena cava superior externa. 



b. Vena cava superior interna. 



c. Vena cava inferior. 



It is evident that the free entrance of the blood would be consider- 

 ably protracted, if the currents were permitted to meet one another 

 in such opposite directions. In order to prevent this, the atrium is 

 provided vnth two broad valvulse, the inferior across the orifice of 

 the V. cava inferior, the superior across that of the v. cava superior 

 externa ; their free margins run in the direction of the current of 

 the inner v. cava superior. When we bring those two valvulse into 

 the most natural position possible, it becomes evident that they not 

 only prevent a backward motion of the blood from the atrium during 

 its systole, but also modify the directions of the currents from the 

 venae during the diastole ; so that the current from the v. cava supe- 

 rior externa is turned more outwards and more to the left, that from 

 the V. cava inferior more inwards and more to the left, whilst the 

 third current appears to preserve its direction (thus). 



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The two vense pulmonales enter the left atrium by two distinct ori- 

 fices, one at the side of the other. The left ventricle is very small, 

 and does not emit a blood-vessel ; it communicates with the right 

 ventricle by a large opening, which can be completely shut by either 

 of the two large valvulse situated at each of the ostia venosa. The 

 right ventricle has a conns arteriosiis, which is as wide as the ven- 

 tricle itself. The arteria pulmonalis is single, whilst the two aortse 

 have separate lumina ; each of those arteries has the usual pair of 

 valvulse at its origin. 



The trachea has the cartilaginous rings not closed on the dorsal 

 side, and is di\-ided into the two bronchi at some distance from their 



