Text book of zoology / by J.E.V. Boas ; translated by J.W. Kirkaldy and E.C. Pollard.

Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Text book of zoology / by J.E.V. Boas ; translated by J.W. Kirkaldy and E.C. Pollard. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    enveloped by a thin sheath, the sarcolemma, which is wanting in smooth as well as in striped muscle cells. The fibres are usually cylindrical, and are rounded, rarely branched or forked, at the ends; they are often of considerable length. In the Arthropoda the whole] and in the Vertebrata the greater part, of the musculature consists of striated muscle fibres, which like the striped muscle cells, contract with greater rapidity, and with greater force, than the smooth muscle cells. Muscle cells and fibres may not only foim large tracts of tissue, but they may also occur as isolated secondaiy constitu- ents of the connective tissue; where these are very numerous and the connective tissue is scanty, an appearance of musculai- tissue is produced. This shows the inti- mate relation between connective tissue cells and muscle cells, which is further demonstrated, in the case of the scattered muscle elements, by the occuiTence of connective tissue cells which have been partially modified into muscle cells. Some- times, like epithelial cells, muscle cells are held together by cement substance. 4. Nervous tissue. The contraction of muscle cells* is brought about by stimuli received from ganglion cells, each of which has a thread-like prolongation often of considerable length (Fig. 15, 2). At its free end each of these processes breaks into a tuft of branches which lie closely upon the muscle cell; sometimes a process gives off branches on its course, and these are attached to muscle cells. Besides these long processes, the ganglion cell may also give origin to numerous shorter branching offshoots, which do not pass to muscle cells. Ganglion cells of this description are called motor: there is another kind, the sensory (Fig. 15, 4), which are, externally, just like the motor ones, but receive, by their long processes, impressions from the outer world. The process may, for instance, go to the epithelium covering the surface of the body, and branch between its cells. {See the section on Sense Organs, p. 18). The ganglion cells occur in groups, comprising both kinds. They are attached to one another by some of the prolongations; those of one cell do not as a rule, however, pass directly to another, but Fig. 14. Connective tissue cell (1), smooth muscle cells (3—5), and a cell (2) which is undergoing transformation into a muscle cell. From the urinary bladder of the Salamander. •— After Flamming. * Under muscle ceUs, smooth and striped muscle cells and also muscle fibres are included.