304 THE HEART. 



the left border, whilst the posterior furrow approaches nearer to the right 

 border of the heart, the right ventricle forming more of the anterior, and 

 the left more of the posterior surface of the organ. Within the transverse 

 and longitudinal furrows are placed the proper nutrient vessels of the heart, 

 the coronary or cardiac arteries and veins, with the lymphatic vessels and 

 nerves imbedded in fatty and connective tissue. 



INTERIOR OF THE HEART. 



GENERAL DESCRIPTION. Considered in respect of function, the heart is a 

 double organ, composed of a right and a left part, each consisting of an 

 auricle and a ventricle. The right portion receives into its auricle from 

 the two vense cavse and coronary veins the dark venous blood returning 

 from the various parts of the body and from the heart itself, and, by means 

 of its ventricle, propels that blood through the pulmonary artery into the 

 lungs. The red blood returning from the lungs by the pulmonary veins, 

 reaches the left auricle of the heart, and is forced onwards by the left 

 ventricle, through the aorta and its branches, into every part of the body. 

 The right and left divisions of the heart present in various respects a 

 similar anatomical structure, and the features which are common to both 

 may here be shortly referred to before passing to those which are peculiar to 

 one auricle or ventricle. 



Endocardium. The interior of the whole heart is invested with a lining 

 membrane, similar in general appearance to the visceral layer of peri- 

 cardium which covers the exterior, but belonging to the class of vascular 

 lining membranes, and continuous with that of the blood-vessels. This 

 internal lining, or endocardium, is a thin transparent membrane, differ- 

 ing slightly on the two sides of the heart. On the left side of the heart 

 it is continuous with the lining membrane of the pulmonary veins and 

 aorta, and is usually found more opaque than on the right side, whence 

 it is prolonged into the veins of the body and into the pulmonary 

 artery. 



According to Theile, the endocardium is very thin on the musculi pectinati of the 

 auricles and on the columnse carneae of the ventricles. It is thicker, however, on the 

 smooth walls of the auricular and ventricular cavities, and on the musculi papillares, 

 especially near their tips. It is, on the whole, thicker in the auricles than in the 

 ventricles, and attains its greatest strength in the left auricle. In both auricles the 

 endocardium consists of three layers. On the free surface is an epithelial stratum of 

 polygonal cells. Beneath the epithelium is a network of elastic fibres, often con- 

 taining portions of fenestrated membrane ; and connecting the latter to the muscular 

 substance of the heart, is a layer of areolar tissue.; Purkinje and Eaeuschel (De 

 Arteriarum et Venarum Structure. Breslau, 1836.) found elastic fibres beneath 

 the endocardium in both auricles, and in the corpora Arantii, but not in the 

 ventricles. ( 



The auricles are each of them divisible into a large cavity, called the 

 atrium, or sinus venosus, and a much smaller part in front, the auricular 

 appendage, auricula, or auricle propei. The anterior of the atrium pre- 

 sents smooth walls in the greater part of its extent, but the walls of the 

 auricular appendages are thrown into closely set reticulated bands, which 

 in the right extend also into the sinus, and are named musculi pectinati. 

 The auricle, both on the right and the left side, receives the blood from 

 the veins, and transmits it into the corresponding ventricle by the auriculo- 

 ventricular opening. 



