others to the blood being cooled in its passage through the lung, and therefore occupying a smaller space when it reaches the left side of the heart. Haller and Meckel' assert, that it is dependent upon the kindof death; that if the right ventricle be usually more capacious, it is owing to the lung being one of the organs that yields first, thus occasioning accumulation of blood in the right cavities of the heart; and they state that they succeeded, in their experiments, in rendering either one or the other of the ventricles more capacious, according as the cause of death arrested first the circulation in the lung or in the aorta; but the experiments of Legallois3 and Seiler, especially of the former, upon dogs, cats, Guinea pigs, rabbits, the adult, the child, and the stillborn foetus, with mercury poured into the cavities, have shown that, except in the foetus, the right ventricle is more capacious, whether death has been produced by suffocation, in which the blood is accumulated in the right side of the heart, or by hemorrhage; and Legallois thinks, that the difference is owing to the left ventricle being more muscular, and, therefore, returning more upon itself. The capacity of each of the ventricles in the full-sized heart has been estimated at about two fluid ounces; but by Valentin' at more than double, and by Volkmann more than treble that amount.

The two hearts, united together by a median septum, form, then, one organ, which is situate in the middle of the chest, (see Fig. 79,) between the lungs, and, consequently, in the most fixed part of the thorax. Figure 100 is modified from one carefully made from nature by Dr. Pennock. It represents the normal position of the heart and great vessels.

According to Carus,' the weight of the heart compared with that of the body is as 1 to 160. M. J. Weber found the proportion, in one case, to be 1 to 150; Dr. Clendinning" that of the male to be 1 to 160; that of the female 1 to 150; and Laennec considered the organ to be of a healthy size when equal to the fist of the individual. M. Cruveilhier estimates the mean weight at six or seven ounces. M. Bouillaud" weighed the hearts of thirteen subjects, in whom, from the general habit, previous state of health, and mode of death, there was every reason to believe that they were in the natural state. The mean was eight ounces and three drachms. From all his data he is led to fix the average weight of the heart, in the adult, from the 25th to the 60th year, at from 8 to 9 ounces. Dr. Clendinning carefully examined nearly four hundred hearts of persons of both sexes, and of all ages

Element. Physiol., iv. 3, 3.

2 Handbuch der Menschlichen Anatomie, Halle, 1817, s. 46; or the translation from the French version, by Dr. Doane, Philad., 1832.

Dict. des Sciences Médicales, v. 440.

Art. Herz. in Pierer's Anat. Physiol. Real Wörterb., iv. 32, Leipz., 1821.

5 Euvres, Paris, 1824.

6 Quain and Sharpey's edit. of Quain's Human Anatomy, Amer. edit., by Leidy, ii. 487, Philad., 1849. 7 Lehrbuch der Physiologie des Menschen, i. 415.

Medical Examiner, April 4, 1840.

9 Introduction to Coinp. Anat., translated by R. T. Gore, Lond.,

1827.

10 Hildebrandt's Handbuch der Anatomie, von E. H. Weber, Braunschweig, 1831, Band. iii. s. 125.

"Journal of the Statistical Society of London, July, 1838. 12 Traité Clinique des Maladies du Cœur, &c., Paris, 1835.

VOL. I.-22

above puberty. The average weight was about nine ounces avoirdupois, much less than that observed by Dr. John Reid,' who found

S. Outline of sternum. C, C. Clavicles. 1, 2, 3, 4, 5, 6, &c. Ribs. 1, 2, 3, 4', 5', 6', &c. Cartilages of ribs. 4. Right and left nipples. a. Right ventricle. b. Left ventricle. c. Septum between ventricles. d. Right auricle. e. Left auricle. f. Aorta. f'. Needle passing through aortic valves. g. Pulmonary artery. g. Needle passing through valves of pulmonary artery. h. Vena cava descendens. i. Line of direction of mitral valve; dotted portion posterior to the right ventricle. i. Needle passed into mitral valve at its extreme left. k. Line of tricuspid valve. 0. Trachea.

the average weight of the male heart-of 89 weighed-to be 11 oz. and 1 dr.: and of the female heart-of 53 weighed-to be 9 oz. and dr. The weight and dimensions of the organ, according to Lobstein and Bouillaud, are as follows:-Weight, 9 to 10 ounces; length from base to apex, 5 inches 6 lines; breadth at the base, 3 inches; thickness of walls of left ventricle, 7 lines; do. at a finger's breadth above the apex, 4 lines; thickness of walls of right ventricle, 2 lines; do. at apex, a line; thickness of right auricle, 1 line; do. of left auricle, a line. M. Bizot' has given the following measurements, taking the average of males from 16 to 89 years.

1 Lond. and Edinb. Monthly Journal of Med. Science, April, 1843, p. 322.

2 For the results of M. Bizot's researches, to ascertain the dimensions of the heart and arteries, see Mémoires de la Société Medicale d'Observation, Paris, 1837; and Hope on the Diseases of the Heart, Amer. edit., by Dr. Pennock, p. 234, Philad., 1842.

8

In the female, the average thickness is something less. Dr. Ranking' has published the results of measurements, evidently made with accuracy, of upwards of 100 hearts,-care being taken to exclude all those that exhibited any trace of organic change. The following are the mean admeasurements. Of 15 male hearts, the mean circumference was 9ths inches; of 17 female hearts, 81gths inches. The mean length of the male heart was 418ths inches; of the female, 43gths. The mean thickness of the left ventricle, in the male, was ths of an inch; in the female, 3ths; of the right ventricle, in the male, ths; in the female, ths. The septum ventriculorum has, in the male, a mean thickness of ths of an inch; in the female, 14ths. The aortic orifice, in the male, had a mean circumference of 24ths inches; the right auriculo-ventricular orifice, 43ğths inches; the left auriculo-ventricular orifice, 34gths inches. The corresponding parts of the female were relatively less. Dr. Ranking infers, that the heart of the male is larger than that of the female,-that the length of the healthy heart is to its circumference rather less than 1 to 2,-that the thickness of the parietes of the right ventricle to the left is as 1 to 3 nearly:-that the pulmonary artery is slightly wider than the aorta; and, lastly, that the right auriculo-ventricular opening is considerably larger than the left.

It need scarcely be said, that the weight and dimensions of the organ must vary according to the age, sex, &c., of the individual. M. Bizot found, that the influence of stature on its size was slight; and not such as might have been expected à priori; for, in individuals of the male sex above sixty inches, and in females above fifty-five inches, in height, the mean dimensions of the organ, especially its breadth, were less than in persons of a lower stature. He found the width of the shoulders furnish a better proportionate standard of its measurement, the distance between the acromial point of the clavicles, and the length and breadth of the heart increasing in a tolerably regular ratio. Numerous measurements of the organ have been made on children by MM. Rilliet and Barthez; whence it results: First. That its circumference does not augment in proportion to age. It is nearly the same from 15 months to five years and a half; and from the latter age it goes on increasing irregularly until puberty. Secondly. The distance from the base to the apex is nearly one-half the total circumference at the base of the ventricles. Thirdly. The maximum thickness of the parietes of the right ventricle varies but little according to age. It is generally 0-078 Eng. inch to the age of six years; and after this from 0-118 to 0.157. Fourthly. The maximum thickness of the left ventricle remains below 0-393 Eng. inch, until six years of age. Later, it is habitually 0-393, or a little more. Fifthly. The proportion between the thickness of the two ventricles is generally, as stated by M. Guersant, as 3 to 1, or 4 to 1, rather more than less. Sixthly. The maximum thickness of the septum is nearly the same as that of the left ventricle, a little more rather than less. Seventhly. The seat of the maximum thickness of the right ven

1 London Medical Gazette, No. xxiv., 1842.

2 Mémoires de la Société Médicale d'Observation de Paris, tom. 1ère, Paris, 1836.

3 Traité Clinique et Pratique des Maladies des Enfants, iii. 662, Paris, 1843.

tricle is at the base, and near the auriculo-ventricular orifice; that of the left ventricle one or two centimètres (in. 0·393 or 0·796) from the base; and that of the septum from two to three centimètres (in. 0.796 to 1.171). Eighthly. The size of the right auriculo-ventricular orifice remains nearly the same until the age of 5 years; it scarcely increases in size up to the age of 10; but then augments more manifestly. Ninthly. The left auriculo-ventricular orifice, which is always smaller than the right, increases a little more regularly than it with age, and frequently has the same dimensions as the distance from the base of the heart to its apex. Tenthly. The aortic orifice presents but a slight augmentation from 15 months to 13 years of age. Eleventhly. The pulmonary artery, on the other hand, increases notably from the age of six years to eight, so that although before this period it is equal to or scarcely greater than the aortic orifice, afterwards it is commonly much larger. They did not find any marked difference between the male and female heart in children.

The heart is surrounded by its proper capsule, called pericardium,— a fibro-serous membrane, composed of two layers. The outermost of these is fibrous, semi-transparent, and inelastic; strongly resembling the dura mater in its texture. Its thickness is greater at the sides than below, where it rests upon the diaphragm; or than above, where it passes along the great vessels which communicate with the heart. The inner layer is of a serous character, and lines the outer, giving the polish to its cardiac surface; it is then reflected over the heart, and adheres to it by areolar substance. Like other serous membranes, it secretes a fluid, termed liquor pericardii, to lubricate the surface of the heart. This fluid is always found in greater or less quantity after death; and a question has arisen as to the amount that should be considered morbid. This must obviously vary according to circumstances. In the healthy condition, it is seldom above a tea-spoonful. When its quantity is augmented, the disease hydropericardium exists. Its great use probably is to keep the heart constantly moist by the exhalation effected from it; and, also, to restrain the movements of the organ, which, under the influence of the emotions, sometimes leaps inordinately. If the pericardium be divided in a living animal, the heart is found to bound, as it were, from its ordinary position; and hence the expression," leaping of the heart,"-during emotion, is physiologically accurate.

b. Arteries.

Arteries are solid, elastic tubes, which arise, by a single trunk, from the ventricle of each heart, and gradually divide and subdivide, until they are lost in the capillary system. The large artery, which arises from the left ventricle, and conducts the blood to every part of the body, even to the lungs, so far as regards their nutrition,-is the aorta; and that, which arises from the right ventricle and conveys venous blood to the lungs for aeration, is the pulmonary artery. Neither the one nor the other is the continuation of the proper tissue of the ventricles; the inner membrane is alone continuous-the muscu lar structure of the heart being united to the fibrous coat of the arteries by means of an intermediate fibrous tissue. The aorta, as soon

as it quits the left ventricle, passes beneath the pulmonary artery, is entirely concealed by it, and ascends to form a curvature with the convexity upwards, the summit of which rises to within three quarters of an inch or an inch of the superior edge of the sternum. This great curvature is called the cross or arch of the aorta. The vessel then passes downwards, from the top of the thorax to nearly as far as the sacrum, where it divides into two trunks, one of which proceeds to each lower extremity. In the whole of this course, it lies close to the spine, and gives off the various branches that convey arterial blood to the different parts of the body. Of the immense multitude of these ramifications an idea may be formed, when we reflect, that the finest pointed needle cannot be run into any part of the surface of the body, without blood-probably both arterial and venous-flowing. larger arteries are situate deeply; and are thus remote from external injury. They communicate freely with each other, and their anastomoses are more frequent as the arteries become smaller and farther from the heart. At their final terminations, they communicate with the veins and lymphatics.

The

It has been a common, but questionable belief, that the branches of the aorta, when taken collectively, are of much greater capacity than the parent trunk, and that this excess goes on augmenting; so that the ultimate divisions of an artery are of much greater capacity than the parent trunk. Hence, the arterial system has been considered to represent, in the aggregate, a cone, whose apex is at the heart, and base in the organs; but as all the minute arterial ramifications are not visible, it is obviously impracticable to discover the ratio between their united capacity and that of the aorta at its origin: yet the problem has been attempted. Keill, by experiments made on an injected subject, considered it to be as 44,507 to 1:-J. C. A. Helvetius and Sylva as 500 to 1. Sénac estimated, not their capacities but their diameters, and conceived the ratio of these to be as 118,490 to 90,000; and George Martine affirmed, that the calibre of a parent arterial trunk is equal to the cube root of the united diameters of the branches. It will be shown, however, hereafter, from the observations of M. Poiseuille and Mr. Ferneley, that the notion of the much greater capacity of the branches than of the parent trunk is a fallacy. The whole subject will be referred to in another place.

The pulmonary artery strongly resembles the aorta. Its distribution. has been already described as a part of the respiratory organs.

The arteries are composed of different coats in superposition, respecting the number of which anatomists have not been entirely of accord. Some have admitted six; others five; others four; but at the present day, three only are perhaps generally received;-first, an external, areolar or cellular, called also nervous, and cartilaginous by Vesalius, and tendinous by Heister, which is formed of condensed areolar substance, and has considerable strength and elasticity, so that if a ligature be applied tightly round the vessel, the middle and internal coats may be completely cut through, whilst the outer coat may remain entire. Scarpa is not disposed to admit this as one of the coats. He considers

Haller, Element. Physiolog., lib. ii., sect. 1, 18, Lausan., 1757.