TUK CMCULATOl.y .\rr.\H.\TU8. 





wall or roof, and tbo auriculo-ventrirular ojinu'ii'/, which occupii-s the whole 

 floor of tho cavity. This orifice has been already described. 



Tbo anterior cul-de-sac is in tho appendix auriculas ; it is divided by a 

 groat number of muscular columns of the second and third onlrr- (wMMitt 

 pectinati), into deep and complex areolro. 



Tbo posterior wall responds to tho interaurictilar septum ; it is smooth, 

 and usually marked by an oblique and more or less deep cul-de-sac (or de- 

 pression), the remains of Botal's foramen. This depression is surrounded 

 by the ring of Vicussens (annulus ovalis) and is named tho fossa ovalis ; it is 

 only separated from the left auricular cavity by a thin membrane, a vestigo 

 of the valve circumscribing the interauricular opening in tho foetus. 



The external wall is areolated, and perforated behind and below by two 

 orifices, tho largest of which is tho embouchure of tho posterior vciisi 

 cava, the other tho opening of the large coronary vein. Both are destitute 

 of valves, though these are found at a short distance in the coronary vein. 

 The bronchial vein sometimes opens separately beside the latter. 



The internal icatt is smooth. 



Tho superior wall, or roof of the auricle, shows the openings of the 

 anterior vena cava and vena azygos ; tho latter only is provided with valves, 

 which ore, however, not always present. On this wall are also remarked, in 

 front, areolao separated by muscular columns. 



The thickness of the right auricular walls is very irregular, in conse- 

 quence of tho reliefs sculptured on the inner face of that cavity. In some 

 points it is about the third of an inch, and in others, particularly in the 

 small cuh-dc-sac formed by tho reticulations, it is sometimes so thin as 

 to appear exclusively formed by the union of tho external and internal 

 serous membrane. 



(When the vena azygos opens behind, there is between it and the orifice 

 of tho anterior vena cava, a muscular lamella with a free concave border, 

 which forms a kind of valvo whose extent is very variable. Behind this vena 

 cava is a thick eminence, tho ttiberculum Loweri ; this has tho form of a 

 crescent, open in front, and elongated from right to left at the superior 

 border of the septum. The anterior, or left border of the fossa ovalis, is 

 thin and prominent, and constitutes the Eustachian valve : a muscular 

 membranous fold of a semilunar shape, with a concave free border directed 

 to tho right and behind. It is of little use in animals, because of their 

 horizontal position. Immediately beneath tho posterior vena cava, and 

 between it and the coronary vein, is a small membranous crescent the nil re 

 of TJiebesius.) 



C. EED-BLOOD (OR AORTIC) HEART. This is also called the posterior 

 Jieart, and more frequently the left heart, because it is situated behind and 

 to the left of the dark-blood heart. Its general disposition otherwise exactly 

 resembles that of tho latter receptacle. 



LEFT VENTRICLE. This is a cylindro-conical cavity, whoso transverse 

 section gives an irregularly circular figure. Its walls attain a thickness of 

 from 1 to l inches, except towards the apex of tho heart, whore they aro 

 extremely thin. They are loss reticulated than those of tho right ventricle, 

 and exhibit several columns of tho second order, as well as two enormous 

 muscular pillars an external and internal, for tho attachment of the tendons 

 of the auriculo-ventricular valvo. Tho apex of tho cavity forms a re- 

 ticulated cul-de sac, which occupies tho point of tho heart. The base is 

 perforated by tho auriculo-vontricular and the aortic openings. Tho auriculo- 

 ventricular opening, precisely similar to that of the right ventricle, is 





