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This illustration shows a representation of the circulation of the blood, in its essential features. The arrows indicate the course of the blood. a, arteries; aur., auricle or receiving portion of the heart; d, digestive tract; c. d., capillaries of the digestive tract; c.r., capillaries of the respiratory organs; c.s., capillaries of the system; va., valves; ve, veins; vt, ventricle.

Blood Circulation

This illustration shows a representation of the circulation of the blood, in its essential features.…

Capillaries. 1: Vein; 2: Artery; 3: Capillary.

Capillaries

Capillaries. 1: Vein; 2: Artery; 3: Capillary.

Capillaries from the vitreous humor of a fetal calf. Two vessels are seen connected by a cord of protoplasm, and clothed with an adventitia, containing numerous nuclei. a, insertion of this cord into the primary walls of the vessels.

Capillaries from Vitreous Humour of Calf

Capillaries from the vitreous humor of a fetal calf. Two vessels are seen connected by a cord of protoplasm,…

Capillaries (C) in the web of the frog's foot connecting a small artery (A) with a small vein (V).

Capillaries in Frog's Foot

Capillaries (C) in the web of the frog's foot connecting a small artery (A) with a small vein (V).

Development of capillaries in the regenerating tail of a tadpole. a b c d, sprouts and cords of protoplasm.

Development of Capillaries of a Tadpole

Development of capillaries in the regenerating tail of a tadpole. a b c d, sprouts and cords of protoplasm.

Development of capillaries in the regenerating tail of a tadpole. a b c d, sprouts and cords of protoplasm. The sprouts and cords of protoplasm have become channeled out into capillaries.

Development of Capillaries of a Tadpole

Development of capillaries in the regenerating tail of a tadpole. a b c d, sprouts and cords of protoplasm.…

A large capillary from the frog's mesentery eight hours after irritation had been set up, showing emigration of leucocytes. Labels: a, Cells in the act of traversing the capillary wall; b, some already escaped.

Capillaries Showing Emigration of Leucocytes

A large capillary from the frog's mesentery eight hours after irritation had been set up, showing emigration…

Diagrammatic representation of a capillary seen from above and in section. Labels: a, the wall of the capillary with, b, the nuclei; c, nuclei belonging to the connective tissue in which the capillary is supposed to be lying; d, the canal of the capillary.

Diagram of a Capillary

Diagrammatic representation of a capillary seen from above and in section. Labels: a, the wall of the…

Isolated capillary network formed by the junction of several hallowed-out cells, and containing colored blood-corpuscles in a clear fluid. Labels: p, p, pointed cell-processes extending in different directions for union with neighboring capillaries.

Capillary Network

Isolated capillary network formed by the junction of several hallowed-out cells, and containing colored…

A small portion of the capillary network as seen in the frog's web when magnified about 25 diameters. Labels: a, a small artery feeding the capillaries; v, v, small veins carrying blood back from the latter.

Capillary Network

A small portion of the capillary network as seen in the frog's web when magnified about 25 diameters.…

A small portion of the capillary network as seen in the frog's web when magnified about 25 diameters. Labels: a, a small artery feeding the capillaries; v, v, small veins carrying blood back from the latter.

Capillary Network

A small portion of the capillary network as seen in the frog's web when magnified about 25 diameters.…

A network of capillaries.

Capillary Network

A network of capillaries.

Diagram of circulation. Labels: L, left side of heart; R, right side of heart; a,a,a arterial system; b,b, capillaries; c,c,c veins; Alim., alimentary canal; Liv., liver; p, portal vein; H,hepatic vein; Lymph., lymphatic duct and tributaries; Pulm., lungs; Pa, pulmonary artery; Pu, pulmonary vein.

Diagram of Circulation

Diagram of circulation. Labels: L, left side of heart; R, right side of heart; a,a,a arterial system;…

Circulation in frog's foot under a microscope. Labels: A, walls of capillaries; B, tissue of web lying between the capillaries; C, cells of epidermis covering web (these are only shown in the right-hand and lower part of the field; in the other parts of the field the focus of the microscope lies below the epidermis); D, nuclei of these epidermic cells; E, pigment cells contracted, not partially expanded; F, red blood corpuscle (oval in the frog) passing along capillary -- nucleus not visible; G, another corpuscle squeezing its way through a capillary, the canal of which is smaller than its own transverse diameter; H, another bending as it slides round a corner; K, corpuscle in capillary seen through the epidermis; I, white blood corpuscle.

Circulation in a Frog's Foot

Circulation in frog's foot under a microscope. Labels: A, walls of capillaries; B, tissue of web lying…

"The arteries of the hand, showing the communications or anastomoses of different arteries and the fine terminal twigs given off from the larger trunks; these twigs end in the capillaries which would only become visible if magnified. R, the radial artery on which the pulse is usually felt at the wrist; U, the ulnar artery." —Martin, 1917

Hand Arteries

"The arteries of the hand, showing the communications or anastomoses of different arteries and the fine…

The heart is the organ that propels the blood and causes it to circulate through the arteries, veins, and capillaries.

Heart

The heart is the organ that propels the blood and causes it to circulate through the arteries, veins,…