THE HEART AND VASCULAR SYSTEM. 



THE PERICARDIUM is a conical, membranous, closed sac, 

 surrounding the heart and the roots of the great vessels. It 

 occupies the greater part of the middle mediastinum, its apex 

 upward, its base downward and attached to the central tendon 

 of the diaphragm. It is a fibre-serous membrane, consisting of 

 an outer fibrous coat and an inner serous coat. The latter is 

 composed of a visceral layer reflected over the heart and vessels, 

 and a parietal layer lining the inner surface of the fibrous sac. 

 It secretes a thin, serous fluid. 



The fibrous coat becomes continuous above with the deep 

 layer of the cervical fascia, being prolonged upward on the 

 outer surfaces of all the great vessels, except the inferior vena 

 cava. 



THE HEART. 



The heart is a hollow, muscular organ, placed obliquely 

 within the chest, and inclosed within the pericardium. Its 

 base is directed upward and backward, opposite the fifth to 

 eighth dorsal vertebrae; its apex downward to the left, opposite 

 the interspace between the fifth and sixth costal cartilages. Its 

 weight is about ten to twelve ounces in male, eight to ten in 

 female; length five inches, breadth three and a half inches, 

 thickness two and a half inches. 



It is divided into four parts: 



Right auricle, Left auricle, 



Right ventricle, Left ventricle, 



an auricle and ventricle on each side. This division is indicated 

 on both surfaces of the organ by two grooves crossing each other 

 and named, from their position, the longitudinal the inter- 

 ventricular, the transverse the auriculo-ventricular grooves. 



EIGHT AURICLE. The right auricle consists of two por- 

 tions a sinus or atrium and an appendix auricula, which pro- 

 jects to the right side of the origin of the aorta. The walls at the 

 fore and outer part and in the auricular appendage are thick- 

 ened by musculi pectinati. Its interior presents the following 

 parts : 



Openings of the superior and inferior venw cavce, neither 

 of which are protected by valves; 

 (170) 



