280 FUNCTIONS OF NUTRITION. 



The descent of the base of the heart in front toward its apex is 

 due to the contraction of the right ventricle, which occupies most of 

 the anterior surface of the organ, being wrapped round the left ven- 

 tricle from below upward and from right to left, and continuing its 

 course in this direction, as the conus arteriosus, to the base of the pul- 

 monary artery. Its superficial muscular fibres run obliquely from above 

 downward and from right to left, uniting with those of the left ven- 

 tricle at the interventricular sulcus. The base of the heart in an ante- 

 rior view is therefore the upper border of the right ventricle and conus 

 arteriosus; and it is brought downward, by the contraction of the 

 descending muscular fibres, toward the interventricular sulcus and the 

 point of the heart. The principal part of the cardiac mass, in warm- 

 blooded quadrupeds, consists of the left ventricle; while the right 

 ventricle is an additional chamber or covered passage-way, leading to 

 the pulmonary artery, very visible in a front view, owing to its situa- 

 tion, but forming a small portion of the substance of the organ. The 

 relative volume of the two ventricles may be shown by a transverse 

 section of the heart in its contracted condition. The left ventricle 

 forms a thick muscular cone, with its cavity nearly in the centre of 



the cardiac mass; while the right 

 ventricle is a comparatively inconsid- 

 erable layer of fibres attached to the 

 surface of the organ and enclosing 

 a cavity of more linear and flattened 

 form. Its contraction, accordingly, 

 may produce a marked change in the 

 superficial aspect of the heart, with- 

 out causing an important alteration 

 in its entire form. 



TRANSVERSE SECTION OF THE BULLOCK'S ml .. . _,. A i i ,, 



HEART IN THE STATE OF CADAVERIC RIG- The deviation of the heart's apex 

 IDITY.-O. Cavity of the Left Ventricle, toward the right, and its axial rota- 



6. Cavity of the Right Ventricle. .. . , . ,. ,', 



tion in the same direction, 5 at the ven- 

 tricular systole, are caused by the obliquity of the external cardiac 

 fibres, and the mode of their penetration at the apex. The most 

 superficial of these fibres, running obliquely from above downward 

 and from right to left, at the time of their contraction tilt the point 

 of the heart slightly toward the right. Near the apex of the organ 

 they curl round its axis, and suddenly change their direction, passing 

 into the interior of the ventricles as deep-seated fibres, and thence 

 running upward, to terminate in the chordae tendineae and auriculo- 

 ventricular zones. 



They thus form, exactly at the point of the heart, a whorl or vortex 

 of converging fibres. Muscular fibres, arranged in this way, necessarily 

 tend, in contracting, to straighten themselves and untwist the spiral. 

 At the ventricular systole, therefore, the heart rotates on its axis, from 

 left to right anteriorly, and from right to left posteriorly. This pro- 

 duces the twisting movement perceptible at the apex. 



