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the description of the valves. The walls of the left ventricle, which are nearly half an inch in thickness, are, with the exception

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siderably less. The latter condition is adapted to the small amount of force which the auricles require in order to empty themselves

Fig.92.-Network of muscular fibres (striated) from the heart of a pig. The nuclei of

the muscle-corpuscles are well shown. X 450. (Klein and Noble Smith.)

into their adjoining ventricles;

the former to the circumstance of the ventricles being partly filled with blood before the auricles contract.

Size and Weight of the Heart.The heart is about 5 inches long, 3 inches greatest width, and 21 inches in its extreme thickness. The average weight of the heart in the adult is from 9 to 10 ounces; its weight gradually increasing throughout life till middle age; it diminishes in old age.

Structure. The walls of the heart are constructed almost entirely of layers of muscular fibres; but a ring of connective tissue, to which some of the muscular fibres are attached, is inserted between each auricle and ventricle, and forms the boundary of Fibrous tissue also exists at

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the auriculo-ventricular opening. the origins of the pulmonary artery and aorta.

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1 Spectrum of Argand-lamp with Fraunhofer's line's in position 2 Spectrum of Oxyhemoglobin in diluted blood.

3 Spectrum of Reduced Hemoglobin.

Spectrum of Carbonic oxide Hæmoglobin.

5 Spectrum of Acid Hæmatin in etherial solution.

6 Spectrum of Alkaline Hæmatin

7 Spectrum of Chloroform extract of acidulated Ox-bile.
8 Spectrum of Methæmoglobin.
9 Spectrum of Hemochromogen

10 Spectrum of Hæmatoporphyrin

Most of the above Spectra have been drawn from observations by ME W Lepraik FCS.

Danielsson & Comp Lendon lith

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