Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/115

Rh VASCULAR SYSTEM 99 a nmen- ons and eight. Uodes of xarnin- ng living it-art. action, approximating the base of the valves (Faladino). Some of the larger chordse tendinese contain striated muscle (Oehl), whilst a delicate muscular network exists in the valvulre Thebesii (guarding the openings of small veins from the sub stance of the heart into the right auricle) and in the Eus- tachian valve (a crescentic fold of membrane in front of the opening of the inferior vena cava) (Landois). The aortic and pulmonary open ings are guarded by the sig- moid or semilunar valves, each of which consists of three semicircular flaps, each flap being attached by its convex border to the wall of the ar tery, whilst its free border projects into the interior of the vessel. The segments con sist of fibrous tissue covered with endocardium. At the middle of the free border there is a fibro-cartilaginous thick- Fin. 5. View of partial dissection of fibres ening called the nodlllus or m anterior wall of ventricles in a sheep s .. heart, showing different degrees of obli quity of fibres. At the base and apex the superficial fibres are displayed in the in tervening space ; more and more of the fibres have been removed from above downwards, reaching to a greater depth on the left than on the right side, a 1, a 1 , superficial fibres of right ventricle ; b l , b 1, superficial fibres of left ventricle ; 2, superficial fibres removed so as to expose those underneath, which have the same direction as the superficial ones over the left ventricle, but a different direction from those over the right ventricle ; at 3 some of these have been removed, but the direc tion is only slightly different ; 4, trans verse or annular fibres occupying middle of thickness of ventricular walls ; 6, 7, internal fibres passing downwards to wards apex to emerge at the whorl ; c, c, anterior coronary or interventricular groove, over which the superficial fibres cross ; in the remaining part of the groove some of the deep fibres turn back wards into the septum ; d, pulmonary ar tery; e, aorta. (Allen Thomson, Quain s Anatomy.) According to Laennec, the size of the heart is about equal to the closed fist of the individual. Its mean weight is about 9 to 10 oz. John Reid s tables give the average weight in the adult male as 11 oz. and in the female as 9 oz. The proportion of the weight of the heart to that of the body is from 1 to 150 to 1 to 170 (Quain). W. Miiller gives the ratio of heart weight to body weight in the child, and until the body weighs 88 lb, as 176 oz. to 2 2 lb ; when the body weight is from 110 to 200 ft the ratio is 141 oz. to 2 2 ft ; and when the weight of the body reaches 220 ft the ratio is as &quot;123 oz. to 2 2 ft. The volume of the heart, according to Beneke, is as follows : new-born infant, 1 34 cubic inches ; 15 years of age, 9 15 to 976 ; at 20 years, 15 25 ; up to the 50th year, 17 08 cubic inches ; after that there is a slight diminution. There is scarcely any differ ence between the capacities of the two ventricles, although in the ordinary modes of death the right is always found more capacious than the left, probably because it is distended with blood ; the left ventricle after death is usually empty and more contracted. The wall of the left ventricle is much thicker than that of the right. The specific gravity of heart muscle is 1 069. The thickness of the left ventricle in the middle is in man 44 inch and in woman 43 ; that of the right is 16 and 14 inch respectively. The circumfer ence of the tricuspid orifice in man is 4 62 inches and in woman 4 33 ; of the mitral, 4 13 and 3 78 respectively. The circumference of the pulmonary artery is 2 94 inches ; of the aorta 277 ; of the superior vena cava 702 to 1 05 inch ; of the inferior vena cava 1 05 to 1 4 ; and the diameter of the pulmonary veins, 53 to 62. When the hand is applied to the side, a little to the left of the left nipple, and in the interval between the fifth and sixth ribs, a shock or impulse is felt. If the whole hand be placed flat over the region of the heart, one may notice the presence or absence of the heart beat, also its situation and extent, and any alterations in its character. In some rare cases, where there is a congenital fissure of the sternum, the finger can be applied to various parts of the heart s surface, with the integuments and pericardium intervening. Tills mode of examination may be termed palpation. Again, when the ear is applied, either directly, or indirectly by means of the stethoscope, over the position of the heart, sounds are heard the duration and rhythm of which are of physiological significance. This mode is known as auscultation. By percussing over the region corpus Arantii. From this nodulus numerous tendinous fibres radiate to the attached border of the valve, but along the margin of the valve the membrane is thin and desti tute of such fibres. These thin parts are called the lu- nuJse. Opposite each semi- lunar flap there is a bulging of the wall of the vessel, the sinuses of Valsalva. In the aorta these are situated one anteriorly and two posteriorly (right and left). From the anterior arises the right coro nary artery, and from the left posterior the left coronary artery, these vessels being for the supply of blood to the substance of the heart (Quain). r Vent of the heart the anatomical limits of the organ may be exactly de fined, and information obtained as to its actual size, as to any alterations in the relation of the lungs to the heart, and as to the presence or absence of fluid in the pericardium. The direct regis tration of the movements of the heart has been accomplished by the aid of various recording instruments. 1 The movements of the heart consist of a series of contractions Move- whieh succeed each other with a certain rhythm. The period of ments of contraction is called the systole, and that of relaxation the diastole, heart. The two auricles contract and relax synchronously, and these move ments are followed by a simultaneous contraction and relaxation of the ventricles. Thus there is a systole and diastole of the auricles and a systole and diastole of the ventricles. But in each half of the heart the contractions and relaxations of the auricle and the contractions and relaxa tions of the ventricle are suc cessive. Finally, there is a very short period in which the heart is entirely in dia stole. The whole series of movements, from the com mencement of one auricular systole to the commencement of the one immediately follow ing, is known as the cardiac cycle or period of revolution of the heart. In fig. 6 the systole is represented by the curve above the horizontal lines and the diastole by the curve below them. The auri cular changes are traced on the upper line au and those of the ventricle on the lower line vent. The length of the lines represents the total duration of a cardiac revolution. The diagram shows that the auricular systole occupies one-fifth of the total time of a revolution of the heart and the ventricular systole two-fifths, that the auricular systole immediately precedes the ven tricular systole, that the commencement of the ventricular systole coincides with the commencement of the auricular diastole, and that during two-fifths of the total period both auricles and ven tricles are in a state of diastole. There are thus three periods, (1) one of auricular systole, one-fifth ; (2) one of ventricular systole, two-fifths ; and (3) one of repose, two-fifths. The impulse of the apex against the wall of the chest, the moment of which is indi cated by x, occurs at the middle of the time occupied by the ventricular systole. In 1861 Chauveau and Marey obtained a direct record of the movements of the heart of a horse, determined the duration of the events happening in the heart, and measured the endocardiac pres sure by an instrument termed a cardiac sound. When the sound was introduced into the right auricle and right ventricle, the animal being anaesthetized, the tracings shown in fig. 7 were FIG. 6. Diagram showing movements of heart. i I i r^ / 1 l // 3 / 1 j i / h

^/

7, 6 I e ~j L

r ^~ ^_- K -^- ^-- ^^ ^~- . - 4-

m &quot;^ ^ i i // r id e i ( L &amp;gt;./ C u l l 1 1 1 /- t - 1 i/

y / V 3

-^ J h^ K ^

I 1 h - / &quot;,

, r /

I i ^&amp;gt;&amp;gt; i / x --, , t I I- - S i ,/ --

^ L^ &amp;lt;&quot; s . / / -- C _^- Fio. 7. Tracings from the heart of a h upper tracing is from the right aurich and the lowest from the apex of the h time, and the vertical amoui t of pres coincident points in the three nioveme squares represents one-tenth of a secoi obtained. From this diagram we The auricular contraction is less s is indicated by the line ab being i (2) The auricular contraction las as the curve almost immediately ventricle remains contracted for orse, by Chanveau and Marey. The , the middle from the right ventricle, eart. The horizontal lines represent sure. The vertical dotted linns mark nts. The breadth of one of the small d. learn the following facts. (1) u den than the ventricular, as nore oblique than the line c d. s only for a very short time, jegins to descenc, whereas the a considerable time, ai d then 1 See Marey, La Melhode Graphiqve, ut supra.