ANATOMY. 



um is moistened by a serous secretion 

 from the exhalant arteries ; which is col- 

 lected after death into a few drops of a 

 clear light yellow liquor. It is an un- 

 natural increase of this that constitutes 

 dropsy of the pericardium. This fluid 

 in the living state lubricates the opposed 

 surfaces of the heart and pericardium, 

 and thereby facilitates their motion on 

 each other, and prevents their accretion. 



The heart, which is contained almost 

 entirely in the left side of the chest, re- 

 sembles a half cone ; hence we distin- 

 guish in it a basis or broad part, and an 

 apex or narrower portion; a convex and 

 a flat surface. The basis is placed to- 

 wards the right, and backwards; the apex 

 points obliquely to the left, forwards and 

 downwards. The basis is opposite to the 

 seventh or eighth vertebra of the back, 

 and the apex points to the cartilage of 

 the fifth or sixth left rib. The position 

 however varies by the motion of the 

 diaphragm in respiration, as it is drawn 

 down in a strong inspiration, and again 

 rises in expiration. Its position also 

 seems to vary slightly, according to the 

 situation of the body in lying. 



A small portion of the left lung seems, 

 as it were, removed just at the apex of 

 the heart ; so that that part of the viscus 

 is not covered by the lung like the rest, 

 but touches the front of the chest. 



Those cavities of the heart which are 

 called the right are placed in front ; and 

 the left cavities are towards the back 

 part ; so that the epithets anterior and 

 posterior would correspond more nearly 

 with the true position of these parts, than 

 those of right and left. 



The flat surface of the heart looks di- 

 rectly downwards, and rests on the ten- 

 don of the diaphragm; this, therefore, in 

 point of position, is inferior ; the convex 

 surface is turned upwards, forwards, and 

 obliquely towards the left, so that it may 

 be called the superior surface. 



The weight of the human heart, when 

 removed from the body, with its pericar- 

 dium, is from 10 to 15 ounces. 



Like the heart of all warm-blooded 

 animals, this organ consists of two 

 hearts, closely and intimately connected. 

 One of these is concerned with the cir- 

 culation through the body, or the greater 

 irculation ; the other with the circula- 

 tion through the lungs, or the minor cir- 

 culation. These might perform their of- 

 fices, if separate and even distant from 

 each other. Each of these hearts con- 

 sists of two cavities; an auricle, or mem- 

 branous bag, placed at the mouths of the 



veins; a ventricle, or strong muscular 

 organ, placed at the orifice of the artery, 

 and constructed for the purpose of driv- 

 ing the blood into that vessel and it$ 

 branches. 



The two auricles are placed at the ba- 

 sis or broadest part of the heart ; and the 

 two ventricles, composing the chief bulk 

 of the organ, are found in front of the 

 former cavities. 



In the following description of the 

 structure of the heart, we shall trace the 

 parts in the same order in which the 

 blood passes through them. This fluid, 

 then, after circulating through the blood- 

 vessels of the body, after serving the 

 various purposes of nutrition, secretion, 

 &.c. is returned into the right auricle of 

 the heart by three large veins, viz. the 

 superior and inferior vena cava, and the 

 great coronary vein. The properties of 

 this blood have been so altered in its 

 course, that it is necessary for it to be 

 subjected to the action of the atmosphere 

 in the lungs, before it is again fit to be 

 sent into the arteries of the body. The 

 right auricle derives its name of auricle 

 from a small fringed process, which is 

 found at its anterior part ; the rest of the 

 cavity is called the sinus of the vense cavze. 

 The lining of this bag, as indeed that of 

 all the other parts of the heart, consists 

 of a smooth and polished surface. The 

 muscular fibres of the auricle are not nu- 

 merous nor large ; they are arranged in 

 parallel fasciculi, which have been com- 

 pared to the teeth of a comb ; and hence 

 the epithet of musculi pectinati has been 

 given to them. 



The right auricle transmits the blood 

 into the right, anterior, or pulmonary 

 ventricle, through a large circular orifice, 

 called the annulus venosus, or the auri- 

 cular orifice of the ventricle. When this 

 latter cavity contracts, the blood would 

 be driven back towards the auricle, were 

 not this prevented by a valve, called the 

 tricuspidal of triglochine. This valve is 



formed by a production of the 



of 



the heart, divided into three pointed 

 portions. These are tied by tendinous 

 strings to certain projecting packets of 

 the muscular fibres, called the fleshy co- 

 lumns of the ventricle. The structure 

 of the ventricle is very different from 

 that of the auricle. It is a strong mus- 

 cular cavity, adapted to the office of for- 

 cibly projecting the blood through the- 

 arterial ramifications ; whereas the auri- 

 cle is a mere reservoir, holding the blood 

 until the ventricle has emptied itself by 

 its contraction. 



