. Comparative anatomy. Anatomy, Comparative. 144 COMPARATIVE ANATOMY. ||S*ia»fe! B A Fig. 105.—Motor plates. A, from guinea-pig; surface view of muscle fiber: B, from hedgehog; section perpendicular to surface of muscle fiber, g, granular substance of the motor plate; w, striated muscle; n, nerve fiber; , terminal ramifi- cation of the nerve fiber. (From Bremer, Text-book of Histology; after Bohm and Davidoff.) which is probably a nutrient medium rather than ordinary cyto- plasm. The wall of the fiber, much more prominent than an ordinary cell-wall, is called the sarcolemma. Some inves
. Comparative anatomy. Anatomy, Comparative. 144 COMPARATIVE ANATOMY. ||S*ia»fe! B A Fig. 105.—Motor plates. A, from guinea-pig; surface view of muscle fiber: B, from hedgehog; section perpendicular to surface of muscle fiber, g, granular substance of the motor plate; w, striated muscle; n, nerve fiber; , terminal ramifi- cation of the nerve fiber. (From Bremer, Text-book of Histology; after Bohm and Davidoff.) which is probably a nutrient medium rather than ordinary cyto- plasm. The wall of the fiber, much more prominent than an ordinary cell-wall, is called the sarcolemma. Some investigators maintain that extraneous connective-tissue cells may give rise to a second investing membrane reinforcing the inner sarcolemma which is a product of the fiber itself. The alternate dark and light bands on the individual fibril are due to physical differences such that, in polarized light, the dark bands are doubly refractive (anisotropic) while the lighter bands are singly refractive (isotropic). Both the dark and the light bands are traversed by finer markings, as seen under high magnification, so that altogether a Nucleus. Sarcoplasm. Fibrils. Lateral branch. very complex structure in the fibril is indicated. In the act of contracting, pro- found changes occur in the appear- ance and relations of the striations. Undoubtedly the contraction of a fibril is due to specific chemical and physical differentiation within the fibril; the contraction of a fiber is the collective contraction of its fibrils; and the contraction of a muscle is the resultant of the action of its numerous fibers. The relation of an unstriated fiber to its nerve is apparently of the simplest sort. A terminal twig of nerve merely attaches to the surface of the fiber, the end of the nerve often showing a knob-like enlargement. Presumably every striated fiber has a nerve connected to it. The nerve, however, enters a small flat plate of nucleated proto- plasm lying superficially on the muscle fiber.
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