. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 669 this not the case, the absence of the heart might be attended in these malformed productions with an unusual development of muscular power in parts of the vascular system.* In conclusion, we may remark that the argu- ment drawn from the occurrence of circula- tion apparently little impaired through arteries which have been completely ossified for a con- siderable time, seems to be very much in favour of the view we have taken that the heart alone is the cause of the progressive flow of blood through the
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 669 this not the case, the absence of the heart might be attended in these malformed productions with an unusual development of muscular power in parts of the vascular system.* In conclusion, we may remark that the argu- ment drawn from the occurrence of circula- tion apparently little impaired through arteries which have been completely ossified for a con- siderable time, seems to be very much in favour of the view we have taken that the heart alone is the cause of the progressive flow of blood through the arterial tubes. 3. Phenomena of the capillary circulation.— The phenomena of the passage of the blood from the terminations of the arteries into the commencement of the veins through the capil- lary vessels, are highly interesting and impor- tant in many points of view, for the immediate respiratory change which the venous blood undergoes in the pulmonary vessels, and all those alterations of composition which accom- pany nutrition, growth, secretion, and other organic processes connected with the systemic vessels, occur in the smallest ramifications of the pulmonic and systemic circulation, and the morbid state of inflammation as well as the various pathological changes which occur as its consequences are intimately connected with an altered condition of the capillary system. a. Structure and distribution of the capillary vessels.—The name of capillary is generally given to all those minute vessels which form the means of communication, between the small ramifications of the arteries and veins; but there is some difference in the opinion of anatomists and physiologists as to how much of the vascular system ought to be included under the division of the capillary vessels. Some, adhering to the strict meaning of the term, apply it to all the small vessels whatso- ever under a certain size; others hold that between the extremities of the arteries and veins there is always si
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