618 



THE HEART. 



says Mr. Wilson, that a stream forced into the superior, 

 takes a course towards the ostium venosum, or right au- 

 riculo-ventricular opening while the inferior current is 

 directed to the septum auricularum, or fossa ovalis, the 

 natural course of the blood in the foetal state. The outer 

 and posterior walls of the auricle are dilated into a pouch 

 called its sinus, while the superior projecting extremity, 

 with indented edges, from its resemblance to the ear of the 

 dog, gets the name of auricle. 



This portion, together with the sinus, has a number of 

 fasciculi of muscular fibres running parallel to each other, 

 and called, from their resemblance to the teeth of a comb, 

 musculi pectinati. Between these fasciculi the spaces con- 

 tain no muscular fibre. 



The internal wall of this cavity consists of a thin parti- 

 tion called the septum auricularum, which separates it from 

 the left auricle. On the lower part of this septum a de- 

 pression is seen, the fossa ovalis, the margin of which all 

 round is thick and elevated, and termed annulus ovalis. 

 This fossa ovalis corresponds to the opening in the foetus 

 called foramen ovale, through which the blood passed freely 

 and directly from the right auricle to the left, but which, 

 after respiration is established, becomes closed by the sep- 

 tum just mentioned. 



To the left of the Eustachian valve is seen an orifice 

 about the size of the common quill ; this is the opening of 

 the coronary vein of the heart, and is protected by a semi- 

 lunar valve called the valve of Thebesius, which is formed 

 by a duplication of the lining membrane of the auricle, 

 and prevents the blood from regurgitating into the vein. 

 At different points of the auricle, small orifices are seen, 

 called foramina TJiebesii, some of which are regarded as 

 the terminations of veins, while others simply lead into 

 the muscular depressions. 



Eight Ventricle. The passage from the right auricle into 

 the right ventricle is through a large, round opening, the 

 ostium venosum or right auriculo-ventricular opening. A 

 dense white line, termed the right tendon of the heart, 



