Quain's elements of anatomy . , and this may be the firstnode from the cell, or the nerve-fibre may pass two or three or-more nodes before thus cell-process, which usuallyacquires its medullary sheath verysoon after leaving the cell, isoften convoluted over the surfaceof or around the ceU; this isespecially the case in the humanspinal gangha. Its bifurcation,or in other words its junctionwith a nerve-fibre traversing theganglion is often T-shaped. These T-shaped divisions werefirst noticed by Eanvier. Theyhave been found by Retzius in the spinal ganglia of all classes of vertebrat
Quain's elements of anatomy . , and this may be the firstnode from the cell, or the nerve-fibre may pass two or three or-more nodes before thus cell-process, which usuallyacquires its medullary sheath verysoon after leaving the cell, isoften convoluted over the surfaceof or around the ceU; this isespecially the case in the humanspinal gangha. Its bifurcation,or in other words its junctionwith a nerve-fibre traversing theganglion is often T-shaped. These T-shaped divisions werefirst noticed by Eanvier. Theyhave been found by Retzius in the spinal ganglia of all classes of vertebrates above fishes—where the cellsare bipolar like that shown in fig. 154 ; and also in man, in the spinalgangha, in the jugular and cervical ganglia of the vagus, the geniculateganglion of the facial and the Gasserian ganglion of the trigeminal;but not in the otic, the sphenopalatine, the sub-maxihary and the ciliaryganghon, the cells of all of which are multi-polar, and hence resemblethose which are found in the Cells which are transitional in character between the bipolar cells of mostfishes and the unipolar cells with forked process of the higher vertebrates, seem 158 NERVOUS SYSTEM. to occui, as Freud lias sho\vii, in Petromyzon, in wMch, in addition to theordinary bipolar cells, some of tlie cells have their two processes coming off quiteclose to one another, and others are unipolar with a short single process whichsoon bifurcates to form two nerve-fibres jjassing in opposite directions. ORIGINS OR ROOTS OF THE NERVES. The cerebro-spinal nerves, as already said, are connected by one ex-tremity to the brain or to the spinal cord, and this central extremityof a nerve is, in the language of anatomy, named its origin or some cases the root is single, that is, the funiculi or fibres by whichthe nerve arises, are all attached at one spot or along one line or tract ;in other nerves, on the contrary, they form two or more separatecollections, which arise apar
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