506 



RIGHT AURICLE. 



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

 pouch, which is called the Sinus, 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 

 whole 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 cavae, 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. 



} 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 Loweri. P. 



: The thick edge or margin is spoken of as the annulus ovalis. P. 



