. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 684 Biology of the Vertebrates The important generalization that the branches of spinal nerves are mixed, while their roots are not, was independently established over a century ago by the Frenchman Magendie (1783-1855) and by Sir Charles Bell (1774-1842), an Englishman, who has been characterized by Pro- fessor Keith as "an anatomical detective of the highest ; (c) Plexuses.—Whenever an extra large area of the body, such as that of the arms
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 684 Biology of the Vertebrates The important generalization that the branches of spinal nerves are mixed, while their roots are not, was independently established over a century ago by the Frenchman Magendie (1783-1855) and by Sir Charles Bell (1774-1842), an Englishman, who has been characterized by Pro- fessor Keith as "an anatomical detective of the highest ; (c) Plexuses.—Whenever an extra large area of the body, such as that of the arms or legs, is to receive a nerve supply, several spinal nerves may join forces, forming a plexus. A complication of this kind adds materially to the difficulty in precisely tracing out the actual path and sequence of neuronic lines between the central nervous system and specific end organs. It has been shown, however, that each muscle may be excited by several nerves, while any single spinal nerve may in turn affect several muscles. The first four cervical nerves in man form the cervical plexus that supplies the neck. The last four, together with the first and usually the second thoracic nerve, make up the brachial plexus of the arm (Fig. 612). Most thoracic nerves do not ordinarily enter into plexus formation. The twelfth thoracic, all five lumbars, and the first three or four sacrals become involved in the large lum- bosacral plexus which supplies the leg. In all of these plexuses only ventral rami are concerned, including both sensory and motor fibers. In various species of long-bodied fishes and urodeles, which do not use their paired appendages for the support of the body, there frequently occurs, anteriorly and posteriorly along the backbone, a shifting of the girdles and their attached appendages (particularly the pelvic girdle), with a consequent variation in the group of spinal nerves that take part in plexus formation. DeBeer records this fact by saying "Limbs m
Size: 1322px × 1889px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
