553 



THE VASCULAR SYSTEMS 



LEFT APPENDIX 



AURICULAE 



LEFT AURICULO- 



VENTRICULAR 



GROOVE 



and extends from the sternal end of the sixth right costal cartilage behind the lower 

 end of the gladiolus to the apex of the heart. 



The left margin, or margo obtusus, is short, thick, and rounded; it is formed 

 mainly by the left ventricle, but to a slight extent, above, by the left auricle. 

 It extends from a point in the second left intercostal space, about 4.5 cm. from 

 the mesal (middle) line, obliquely downward, with a convexity to the left, to the 

 apex of the heart. 



The Cavities of the Heart. Each of the cavities of the heart is lined by the 

 endocardium, a thin, smooth membrane which gives the glistening appearance 



^'^oi'r internal surfaces and by reduplications forming the valves (mitral and 

 these groove, cxtena n .., .. ;d) di the orifices of 



the right of the apex of the heart. nunication and of the aorta 



pulmonary artery, 

 ae Right Auricle 1 (atrium dex- 

 n) is the larger of the two auri- 

 although its walls are some- 

 khat thinner than those of the 

 ft, measuring about 2 mm. It 

 onsists of two parts, a principal 

 cavity, the sinus venosus, situated 

 osteriorly, and an antero-superior, 

 smaller portion, the auricular ap- 

 pendix. 



The sinus venosus (sinus vena- 

 rum) is the large quadrangular 

 AU R i CL cavity, placed between the two 

 venae cavae. Its walls, which are 

 extremely thin, are connected in 

 front and to the left with the right 

 ventricle, and mesally with the left 

 auricle, but are free in the rest of 

 their extent. 



The right auricular appendix 

 (auricula dextra], so called from its 

 fancied resemblance to a dog's ear, 

 is a small conical muscular pouch, 

 the margins of which present a 

 dentated edge. It projects from ...ie sinu_ rward and toward the left side, over- 

 lapping the root of the aorta. 



The separation of the appendix from the sinus venosus is indicated externally 

 by a groove, the sulcus terminalis (His), which extends from the front of the superior 

 vena cava to the front of the inferior vena cava, and represents the line of union 

 of the sinus venosus of the embryo with the primitive auricle. In the s cavity of 

 the auricle the separation is marked by a vertical, smooth, muscular ridge on the 

 anterior wall, the crista terminalis (His) (Fig. 418). Behind the crista the inter- 

 nal surface of the auricle is smooth, while in front of it the muscle fibres of 

 the wall are raised into parallel ridges resembling the teeth of a comb, and hence 

 named the musculi pectinati. 



To examine the interior of the right auricle, an incision should be made along its right border 

 from the entrance of the superior vena cava to that of the inferior vena cava. A second cut is to 

 be made from the centre of the first incision to the tip of the auricular appendix, and the flap 

 raised. 



1 In the new nomenclature the auricle is called the atrium, and the auricular appendix is called the auricle. 



