506 BIGHT AURICLE. 



the right* ventricle, and are dilated anteriorly into a sac or 

 pouch, which is called the Si7ius, and extends to the right ven- 

 tricle, to which it is united.f 



The upper part of this pouch, or sinus, forms a point with 

 indented edges, which is detached from the ventricle, but lies 

 loose on the right side of the aorta. This point has some 

 resemblance to the ear of a dog, from which circumstance the 

 Vk^hole cavity has been called auricle ; but by many persons 

 the cavity is considered as consisting of two portions : the 

 Auricle, strictly speaking ; and the Sinus Venosus, above 

 described : they however form but one cavity. 



This portion of the heart, or Right Auricle, is of an irregular 

 oblong figure. In its posterior surface, it is indented ; for the 

 direction of the two cavas, at their junction, is not precisely the 

 same; but they form an angle, which causes this indentation. 

 The anterior portion of the auricle, or that which appears like 

 a pouch between the ventricle and the veins, is different in its 

 structure from the posterior part, which is strictly a portion of 

 the veins. It consists simply of muscular fibres, which are 

 arranged in fasciculi that cover the whole internal surface : this 

 is also the case with the point, or that part which is strictly 

 called auricle. 



These fasciculi are denominated Musculi Pectinati, from 

 their resemblance to the teeth of a comb. 



That part of the internal surface, which is formed by the 

 septum is smooth, and the whole is covered by a delicate mem- 

 brane. 



On the surface of the septum, below the middle, is an oval 

 depression, which has a thick edge or margin : this is called 

 the Fossa Ovalis.% In the foetal heart, it was the Foramen 

 Ovale, or aperture which forms the communication between 

 the two auricles. 



* In this description the heart is supposed to be in its natural position. 



f At the place of junction of these veins there is a projection, indistinctly 

 seen in man, but very manifest in some of the larger mammalia, called tuber- 

 culum LoTveri. — p. 



% The thick edge or margin is spoken of as the annulus ovalis. — p. 



