Quain's elements of anatomy . nute varicose fibrilsthioug-hout the muscular substance,Avith which they are closely incor-porated. Moreover, another observer,Amdt, who, it is tme, admits theexistence of the end-plate, describesin addition, a complex system of com-municating fibres which extendthroughout the muscular substance,and is the means of bringing theplate into connection with the musclecorpuscles and nuclei. These state-ments, however, have not hithertoreceived confirmation, although En-gelmann and Foettinger have beenled from obsei^vations upon insect-muscles to form a conclusion which
Quain's elements of anatomy . nute varicose fibrilsthioug-hout the muscular substance,Avith which they are closely incor-porated. Moreover, another observer,Amdt, who, it is tme, admits theexistence of the end-plate, describesin addition, a complex system of com-municating fibres which extendthroughout the muscular substance,and is the means of bringing theplate into connection with the musclecorpuscles and nuclei. These state-ments, however, have not hithertoreceived confirmation, although En-gelmann and Foettinger have beenled from obsei^vations upon insect-muscles to form a conclusion whichis at least somewhat analogous, to the effect, namely, that the expansion of the nerve-fibres comes into actual con-tinuity with the isotropous substance of the muscular fibre. But the efl:ect ofsection of a motor nerve in the living mammal—the resulting degenerationextending no further into the muscular fibre than the end-plate itself—is astrong argument agatast the existence of any such anatomical continuity. VOL. II. N. 178 NERVOUS SYSTEM. DEVELOPMENT OF ITERVES. It lias been sliowti by Balfour in elasmobranch fishes, and by Milnes Marshallin the chick, and the same is probably the case in mammals, that the nerve-roots andtheir ganglia, and in all probability the nerves generally, develope as cell-out-growths from the rudimentary central nervous system. The latter, as has longbeen known, is formed by an involution of the ectoderm or epiblast along the middleline of the embryo. So that not only the nerve-cells and -fibres of the centralnervous system (brain and spinal cord), but also the peripheral nerves, and the nerve-cells of the ganglia in connection with them, are of ectodennal origin. No doubtthe connective tissue which enters into the construction of the nerves and nerve-centres, as well as the blood-vessels which are distributed in them, are mesodermal,having become formed as ingrowths from the surrounding mesoderm, but it is as yetuncertain whether this statement
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