. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. NERVOUS TISSUES. 267 IGl A chain of ganglions is situated on each side, near the vertebral foramina, through whicli the cerehro-S2)ii)al nerves issue. These ganglions radiate many nerves, connecting them one with another and with the cerebro-spinal nerves, and ramifying in a plexiform way upon the viscera and coats of the blood-vessels : they con- stitute the 'sympathetic' or 'ganglionic' system in Vertebrates. In the cerebro-spinal nerves the primitive fibre consists of a transparent elastic homogeneous tubular mcmlu-an
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. NERVOUS TISSUES. 267 IGl A chain of ganglions is situated on each side, near the vertebral foramina, through whicli the cerehro-S2)ii)al nerves issue. These ganglions radiate many nerves, connecting them one with another and with the cerebro-spinal nerves, and ramifying in a plexiform way upon the viscera and coats of the blood-vessels : they con- stitute the 'sympathetic' or 'ganglionic' system in Vertebrates. In the cerebro-spinal nerves the primitive fibre consists of a transparent elastic homogeneous tubular mcmlu-ane (neurilemma), fig. 164, a; its contents arc pulpy, homogeneous in the living or recently dead state, and may bo pressed out of the sheath; when treated with water, as in fig. 164, a, or with alco- hol, they Condense into a white layer, giving that colour to the tnbe : within the vvduto substance Rcmak defines a 'flattened l)and,' and Purkinje an ' axis-cylinder.' "\Mien treated with ether, oil-globules co- alesce in the interior, and accumulate around the exterior of the tube, fig. 164, h. The delicacy of the neurileumia, and mobility of its contents, lead, in many cases, to partial dilatations of the tube, of a ' vari- cose' character, jiroljably d\ie to post-mortem influences: in the living or natural state, the primitive nerve- tube or fibre appears to be perfectly cylindrical. The follo^ diameter. Xcrvc tulles nltorcil lij CUV. The following are results of Todd's admeasurements of their in the different vertebrate classes : — Fishes (Eel) j-tj^ts o^ ^^ inch. Reptiles (Frog) -^iwo ^^ ttifVtt of f^i^ inch. Birds ., ,,"'„ n to Wtttt of an inch. ;i 0 0 0 leVs-tOlTToo of an inch.' 2 0 0 0 IMammals Primitive nerve-fibres do not divide or branch; they are associated together, in simple juxtaposition, supported by fine layers of areolar tissue, which condense at the periphery into a common sheath, to which the term ' neiu'ilemma' is commonly, but not properly, given
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