712 HUMAN ANATOMY. 



lower sternum on account of the relation of the right auriculo-ventricular orifice to 

 the middle of that bone ; (^b) increase of percussion area to the right of the sternum 

 because of the distention and dilatation of the right auricle that follow ; and, {c) from 

 the same cause and the resultant backward pressure on the systemic veins, a venous 

 pulse-wave, seen best in the internal and external jugular on the right side, but not 

 infrequently recognizable on both sides, in the subclavian and axillary veins also, or 

 as a systolic expansile impulse in the liver transmitted through the inferior cava and 

 hepatic veins, 



2. Tricuspid stenosis, like that of the mitral valve, is apt to cause a presystolic 

 murmur, and for the same physical reasons. 



3 and 4. Pulmonary insufficiency and stenosis (disease of the pulmonary valves) 

 are so rare and so uncertain in their physical signs as to require mention merely to 

 complete the survey of the group. 



The various forms and degrees of hypertrophy or dilatation of the heart which 

 are associated with the foregoing conditions can be readily understood by con- 

 sidering the increased resistance and correspondingly increased exertion which are 

 brought about by the valvular changes. The essential cause of hypertrophy in the 

 heart, as in other muscles, is increased work. The etiological factors which neces- 

 sitate this should be studied in connection with the anatomy of the heart and have 

 been well summarized by Osier. 



Hypertrophy of the left ventricle alone, or with general enlargement of the heart, 

 is brought about by — 



(a) Conditions affecting the heart itself : (i) Disease of the aortic valve ; (2) 

 mitral insufficiency ; (3) pericardial adhesions ; (4) sclerotic myocarditis ; (5) dis- 

 turbed innervation with overaction, as in exophthalmic goitre, in long-continued 

 nervous palpitation, or as a result of the action of certain articles, such as tea, alcohol, 

 and tobacco. In all of these conditions the work of the heart is increased. In the 

 case of the valve lesions the increase is clue to the increased intraventricular pressure ; 

 in the case of the adherent pericardium, or the myocarditis, to direct interference with 

 the symmetrical and orderly contraction of the chambers. 



i^b) Conditions acting upon the blood-vessels: (i) General arterio-sclerosis, 

 with or without renal disease ; (2) all states of increased arterial tension induced by 

 the contraction of the smaller arteries under the influence of certain toxic substances ; 

 (3) prolonged muscular exertion, which enormously increases the blood-pressure in 

 the arteries ; (4) narrowing of the aorta, as in congenital stenosis. 



Hypertrophy of the right ventricle is met with under-the following conditions : 



( I ) Lesions of the mitral valve, either incompetence or stenosis, which act by in- 

 creasing the resistance in the pulmonary vessels ; (2) pulmonary lesions with obliter- 

 ation of any considerable number of blood-vessels within the lungs, such as occurs 

 in emphysema or cirrhosis ; (3) valvular lesions on the right side occasionally, and 

 not infrequently in the foetus ; (4) chronic valvular disease of the left heart and 

 pericardial adhesions. 



In the auricles simple hypertrophy is never seen ; it is always dilatation with 

 hypertrophy. In the left auricle the condition, develops in lesions at the mitral orifice, 

 particularly stenosis. The right auricle hypertrophies when there is greatly increased 

 blood-pressure in the lesser circulation, whether due to mitral stenosis or to pulmo- 

 nary lesions. Narrowing of the tricuspid orifice is a less frequent cause. 



Hypertrophy or dilatation of the cardiac chambers may cause pressure, some- 

 times injurious, on surrounding structures. 



Great enlargements of the left ventricle, as seen in the bovine heart of valvular 

 disease, may occasion compression of the lower portion of the left lung when a devi- 

 ation of the mediastinum towards the right is prevented. As a rule, such enlarge- 

 ment compresses the lower part of the left lung comparatively little. Enlargement 

 of the right ventricle frequently causes a depression and forward displacement of the 

 left lobe of the liver and the appearance of a pulsating mass in the epigastrium. 



Dilatation of the auricles is more likely to produce serious compression of sur- 

 rounding structures than is that of the ventricles because of the greater fixation of the 

 heart at its upper portion where the auricles are placed. Enlargement of the left 

 auricle has in some cases produced compression of the left bronchus with consequent 



