. Animal and vegetable physiology, considered with reference to natural theology. Biology; Physiology; Plant physiology; Natural theology. CIRCULATION IN THE VERTEBKATA. 1S7 structure. The supply of blood to the heart, beins; in a con- stant stream, produces a gradual dilatation of the cavity which receives it; and the muscular fibres of that cavity are not ex- cited to contraction, until tlicy are stretched to a certain point. But in order effectually to drive the blood into eve- ry part of the arterial system, where it has great resistances to overcome, a considerable impulsive force is requ
. Animal and vegetable physiology, considered with reference to natural theology. Biology; Physiology; Plant physiology; Natural theology. CIRCULATION IN THE VERTEBKATA. 1S7 structure. The supply of blood to the heart, beins; in a con- stant stream, produces a gradual dilatation of the cavity which receives it; and the muscular fibres of that cavity are not ex- cited to contraction, until tlicy are stretched to a certain point. But in order effectually to drive the blood into eve- ry part of the arterial system, where it has great resistances to overcome, a considerable impulsive force is required, im- plying a sudden as well as powerful muscular action. This object is attained, in all vertebrated animals, by providing a second muscular cavity, termed a ventricle, into which the first cavity, or auricle, throws the blood it has received from the veins, with a sudden impulse; and thus the ventricle, be- ing rapidly distended, is excited to a much more quick and forcible contraction than the auricle, and propels the blood it contains into the artery, with an impetus incomparably greater than could have resulted from the action of the au- ricle alone. Fig. 350 represents the heart with its two ca-. vities; D being the auricle, and e the ventricle; together'witli the main trunks of the veins (c, c,) wliich convey the blood into the auricle; and those of the arteries (a,) which receive it from the ventricle for distribution over the whole system. The force of contraction in the principal cavity ofi the heart being tlius increased, it becomes necessary to provide. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Roget, Peter Mark, 1779-1869. Philadelphia, Carey, Lea & Blanchard
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