A manual of elementary zoology / by L.A. Borrodaile.

  • Lancelot Alexander Borradaile
Date:
1945
Catalogue details

Licence: In copyright

Credit: A manual of elementary zoology / by L.A. Borrodaile. Source: Wellcome Collection.

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    defence against the attacks of bacteria and other micro- organisms. In a later chapter (p. 123) we shall consider the warfare which its cells wage against these enemies. The preceding paragraph must not be taken to indicate that the blood comes itself into contact with Lymph. the tissues. The blood vessels are completely closed, and the tissues are actually bathed by another fluid, known as lymph, which is produced by exudation through the capillary walls. This fluid is gathered by small lymphatic vessels into the big lymph sacs already mentioned, whence it is pumped back into the veins by two pairs of small contractile sacs known as lymph hearts. One pair of these lies below the scapulae and opens into the sub- scapular veins ; the other lies at the end of the urostyle and opens into the femoral veins. The fluids in the coelomic (pleuroperitoneal and pericardial) cavities are lymph. The pleuroperitoneal cavity communicates with the dorsal lymph sacs by minute openings (stomata) in the membrane which separates it from them. The respiratory organs of the frog are the lungs, the shin, and the mucous membrane of the mouth. Respiration The iungs communicate with the pharynx by way of the glottis, which leads into a short, wide windpipe consisting of the larynx or voice organ only, without the long trachea, or windpipe proper, which is found in animals with necks. The walls of this cavity are supported by a pair of flat arytcenoid cartilages and a very irregular ring, the cricoid cartilage. The lining of the larynx is thrown into a pair of folds, the vocal cords. Between these is a narrow slit, the rim a glottidis, through which the air must pass to and from the lungs. The cartilages are supplied with muscles, by which they can be moved, so as to tighten the vocal chords and bring them close together. In this condition the chords vibrate when air from the lungs is forced between them, and produce a sound which is the croaking of the frog. From the hinder part of the windpipe an opening leads on each side to a short tube known as the bronchus, which begins at once to expand into the lung. The latter is a wide, thin-walled, elastic, highly vascular sac, whose internal surface is increased by numerous folds. The lungs of the frog are not enclosed,
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