These anomalies manifest themselves either by an abnormal excess or deficiency of size. Both conditions may be either congenital or acquired, and are of great importance from their frequent occurrence and the serious and numerous consecutive disturbances to which they give rise.

In order to arrive at a correct opinion regarding an individual case, it is especially necessary for the student to acquire a knowledge of the normal size of the heart and of its individual portions. Many measurements have been made in recent times, and from these a mean or average standard has been deduced.

The results yielded by Bizot's measurements appear to us to be most correct. We will limit ourselves to the dimensions in adults, between the ages of 30 and 49 years.

The following are the mean measurements:

We purpose, in the sequel, making further use of the other results of the labors of Bizot, which possess any degree of interest, and are not opposed to our own observations.

According to Bizot, the heart increases in volume from birth to extreme age; this increase being most considerable to the age of 29, after which it is only appreciable by measurement. Augmentation of volume depends especially on the continuous dilatation of the openings, and on the increase of thickness of the walls of the ventricles, which is always most strongly marked in the case of the left, and is indeed scarcely perceptible in that of the right ventricle. The dilatation of the auriculo-ventricular openings is tolerably uniform, and that of the arterial equally so until middle life, but after that period the opening of the aorta is more rapidly dilated than that of the pulmonary artery, the latter becoming even narrower than the aorta. In children both the arterial openings remain equally wide, till from the sixth to the tenth year. The cavities of the right side of the heart have a greater capacity, and their openings are wider.

Bizot's opinions regarding the influence of sex and bodily frame are, that the dimensions of all the parts collectively are smaller in women than in men; that the auriculo-ventricular openings in particular are narrower whilst the opening of the pulmonary artery is relatively wider in them than in men. In tall persons of either sex, the heart, according to the same authority, is relatively smaller than in persons of shorter stature, while it is larger in broad than in narrow-shouldered persons.

We adopt Bouillaud's data for the walls of the auricles, with a remark, however, that his estimate is too high; according to him, the thickness of the wall of the left auricle is one Paris line and a half, while that of the right auricle is one line.

Laennec proposed to establish a scale for the relative measurement of the size of the heart, and rejected as inefficient all data of the weight and size of the heart that had been obtained without regard to individual bulk. The basis on which he founded his conclusions was, that the heart, including the auricular appendages, should be of a volume equal to that of the fist of the individual, or only in a slight degree either larger or smaller. The walls of the left ventricle should be somewhat more than twice as thick as those of the right one; the left ventricle, when cut open, should remain unclosed, while the somewhat wider right ventricle, which, notwithstanding the thinness of its walls, is furnished with more considerable trabecule, should collapse.

If in the consideration of these data (which are, however, in many respects defective), regarding the relative thickness of the walls of the right and left ventricles, we bear in mind that this relation is not only very commonly, according to Andral's observation, as 1: 3, but still more frequently (see Bizot's data), as 1: 4,1 and that these measurements refer only to middle life, we shall find that Laennec's comparison of the size of the heart with that of the fist deserves considerable attention, remembering that it must be received as simply approximative, and limits itself to cases where there is no apparent disproportion in the size of the fist. We have, therefore, as a general rule, regarded the heart as of a relatively normal size, when it was equal to that of the fist, and when there was an absence, both during life and after death, of any indications of cardiac disease.

The weight of the heart, in its normal condition, has been variously estimated, and may be from eight to ten ounces. (Compare Lobstein, Bouillaud, and Cruveilhier).

1 In all these statements the columnae carnae are not taken into consideration.

A. Abnormal Size

Deviations in the size of the heart depend either on hypertrophy of its muscular substance (augmentation of its mass) or on dilatation of its cavities; while both conditions, with a preponderance of the one or the other, very commonly constitute the basis of the higher degrees of enlargement of the heart, as we shall presently have occasion to show.

Here, as has already been indicated, we will merely consider hypertrophy of the muscular substance. There is, however, a form of disease, for which we know no better denomination than hypertrophy of the endocardium, and of which, however much it may seem to belong to the subject under consideration, we will treat subsequently in connection with endocarditis, a disease with whose products it may easily be confounded, and for which it undoubtedly is frequently mistaken. We will also defer the consideration of hypertrophy of the valves to a subsequent portion of our work.