. Chordate anatomy. Chordata; Anatomy, Comparative. HISTOLOGY 95. from A Fig. 89.— Motor guinea-pig; surface view of muscle fiber: B, from hedgehog; section perpendicular to surface of muscle fiber, g, granular substance of the motor plate; m, striated muscle; n, nerve fiber; , terminal rami- fication of the nerve fiber. (From Bremer, "Text-book of Histology"; after Bohm and Davidoff.) visceral muscle is unstriated. But unstriated muscle occurs in the walls of blood-vessels which lie in the body-wall, in connexion with some skin structures such as hair and certain glands, and als
. Chordate anatomy. Chordata; Anatomy, Comparative. HISTOLOGY 95. from A Fig. 89.— Motor guinea-pig; surface view of muscle fiber: B, from hedgehog; section perpendicular to surface of muscle fiber, g, granular substance of the motor plate; m, striated muscle; n, nerve fiber; , terminal rami- fication of the nerve fiber. (From Bremer, "Text-book of Histology"; after Bohm and Davidoff.) visceral muscle is unstriated. But unstriated muscle occurs in the walls of blood-vessels which lie in the body-wall, in connexion with some skin structures such as hair and certain glands, and also in the iris of the eye. The muscles in the walls of the mouth, pharynx and at least the upper part of the esophagus are striated, and it is said that striated muscle occurs in the wall of the stomach of some fishes. Also the external anal muscle is striated. The muscular part of the diaphragm is derived from the embryonic body- wall and its muscle is accordingly striated. And in all vertebrates the muscle of the wall of the heart is striated. Unstriated muscle fibers in vertebrates are much like those of inver- tebrates. They are ordinarily not over a fraction of a millimeter in length and, in man, much less than a hundredth of a millimeter in diameter. ^^^^»„^^^ They are usually spindle-shaped (Fig. 87^!) ^'"^'^ , lying in the tissue with their tapering ends li,--'" ^ overlapping. B,.- " The somatic striated fibers of vertebrates are enormously larger than unstriated fibers (Fig. 87^, 88). Their diameter may approach a millimeter and their length, not accurately known, doubtless reaches several or many millimeters. But these great fibers are not, in strict sense, single cells. They contain scores or hundreds of nuclei. The myofibrils of striated fibers are much coarser than those of unstriated fibers. They are imbedded in a peculiar fluid sarcoplasm which is probably a nutrient medium rather than ordinary cytoplasm. The wall of the fiber, much more promin
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