The anatomy of the nervous system, from the standpoint of development and function . less conspicuous element. A few cells retain the bipolar form characteristic of all the spinal ganglioncells at an early stage of development (Figs. 21, 40, d). The spinal ganglion cells are each surrounded by a capsule or membranoussheath with nuclei on its inner surface (Fig. 39, ) which is continuous withthe neurilemma sheath of the associated nerve-fiber. The cells forming thecapsule are of ectodermal origin, being derived like the spinal ganglion cellsthemselves from the neural crest. 1 See fine print,
The anatomy of the nervous system, from the standpoint of development and function . less conspicuous element. A few cells retain the bipolar form characteristic of all the spinal ganglioncells at an early stage of development (Figs. 21, 40, d). The spinal ganglion cells are each surrounded by a capsule or membranoussheath with nuclei on its inner surface (Fig. 39, ) which is continuous withthe neurilemma sheath of the associated nerve-fiber. The cells forming thecapsule are of ectodermal origin, being derived like the spinal ganglion cellsthemselves from the neural crest. 1 See fine print, page 45. 64 THE NERVOUS SYSTEM In good methylene-blue preparations and in sections stained by the newersilver methods it is possible to make out many additional details of axon may split into many branches, which subdivide and anastomose,forming a true network in the neighborhood of the cell (Fig. 39, b). From thisnetwork the axon is again assembled and passes on to a typical the axon may be assembled out of a similar plexus which, however, is con- I. Fig. 39.—Neurons from the spinal ganglion of a dog: a, Small cells with unmyelinated axons;b, c, d, e, and/, large cells with myelinated axons; f, typical large spinal ganglion cell showingglomerulus and capsule. The arrow points toward the spinal cord. Pyridin-silver method. nected with the cell by several roots (Fig. 39. c). Some of the fibers give offcollaterals terminating in spheric or pear-shaped end-bulbs. Such an end bulbmay rest upon the surface of its own perikaryon (Fig. 39, d) or elsewhere in theganglion. From the body of some cells short club-shaped dendrites arise, which,however, terminate beneath the capsule- which surround the cells. Based on such details as these Dogiel (1908) has arranged the spinal ganglion cells ingroups and recognizes eleven different types. Two of his eleven types are of special cells of Type VIII resemble the typical spinal ganglion cell in all re
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