. The comparative anatomy of the domesticated animals. Veterinary anatomy. 550 RESPIRATORY APPARATUS IN (The minute polygonal cells lining the air or pulmonary vesicles measure from TffW to ^TD^ of an inch in diameter, and from ^winj <^o ^^5^ of an inch in thick- ness. Between the vesicles is a tra- p's- 328. becular tissue, mainly composed of yellow elastic with a few muscular fibres, some of which are united with the lining membrane to strengthen it, especially around the apertures of communication between the adjoining air-cells. The capillaiy plexuses are so ar- ranged betwee
. The comparative anatomy of the domesticated animals. Veterinary anatomy. 550 RESPIRATORY APPARATUS IN (The minute polygonal cells lining the air or pulmonary vesicles measure from TffW to ^TD^ of an inch in diameter, and from ^winj <^o ^^5^ of an inch in thick- ness. Between the vesicles is a tra- p's- 328. becular tissue, mainly composed of yellow elastic with a few muscular fibres, some of which are united with the lining membrane to strengthen it, especially around the apertures of communication between the adjoining air-cells. The capillaiy plexuses are so ar- ranged between the two layers forming the walls of two adjacent cells, as to expose one of their surfaces to each, in order to secure the influence of the air upon them. These networks are so close, that the diameter of the meshes is scarcely so great as that of the capillaries which enclose them.) Vessels.—The lung is a very vascular organ. The numerous rami- fications it receives divide into two orders—the functional and the nutri- tive vessels. Functional vessels of the lung.— The blood is returned from all parts of the body by the veins, after losing, along with its bright red colour, the properties which render it fit to maintain the vitality of the tissues. It thus arrives at the right side of the heart, whence it is propelled into the lung, there to be regenerated by mediate contact with the air. It is the pulmonary artery which conveys this fluid into the parenchyma of the organ, and by the pulmonary veins it is carried back to the heart. The artery is at first divided into two branches, which ramify, and finally terminate in dense capillary plexuses upon the walls of the infundibula. The veins—innumerable and attenuated at their origin, like the arterial capillaries —terminate in from four to eight principal trunks, which open into the left auricle of the heart. The branch of the pulmonary artery that enters each lobule, is regarded as terminal—that is, it does not anas
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