TERMINATION OF NERVES. 



333 



after leaving the cell, is often convoluted over the surface of or around the cell ; 

 this is especially the case in the human spinal ganglia. Its bifurcation, or in other 

 words its junction with a nerve-fibre traversing the ganglion is often T-shaped. 



These T-shaped divisions were first noticed by Ranvier. They have been found 

 by Retzius in the spinal ganglia of all classes of vertebrates above fishes where the 

 cells are bipolar like that shown in fig. 370 ; and also in man, in the spinal ganglia, 

 in the jugular and cervical ganglia of the vagus, the geniculate ganglion of the 

 facial and the Gasserian ganglion of the trigeminal ; but not in the otic, the spheno- 

 palatine, the sub-maxillary and the ciliary ganglion, the cells of all of which are 

 multi-polar, and hence resemble those which are found in the sympathetic. 



Cells which are transitional in character between the bipolar cells of most fishes 

 and the unipolar cells with forked process of the higher vertebrates, occur, as Freud 

 has shown, in Petromyzon, in which, in addition to the ordinary bipolar cells, some 

 of the cells have their two processes coming off quite close to one another, and 

 others are unipolar with a short single process which soon bifurcates to form two 

 nerve-fibres passing in opposite directions. 



In the embryo the cells of the spinal ganglia are at first spindle-shaped and 

 bipolar (fig. 383. h, i, fig. 387), with one process growing into the spinal cord and 

 the other into the peripheral nerve. Gradually the processes approach one another 

 and eventually come off from the cell by a common stalk (His). 



TERMINATION, OR PERIPHERAL DISTRIBUTION, OF NERVES. 

 It may be stated, generally, and apart from what may apply to special modes of 

 termination, that, in approaching their final distribution, the fibres, medullated and 



Fig. 388. SMALL BRANCH OF A MUSCULAR NERVE OF THE FROG, NEAR ITS TERMINATION, SHOWING 



DIVISIONS OF THE FIBRES. MAGNIFIED 350 DIAMETERS (Kolliker). 



a, into two ; b, into three. 



non-medullated, usually divide into branches, the division in the case of medullated 

 fibres always occurring in the situation of a node of Ranvier (fig. 388). The axis 

 cylinder participates in the division ; and since the white fibres frequently lose their 

 medullary sheath shortly before they terminate, they are then represented by the 

 axis-cylinder and its ramifications, although the primitive sheath may continue some 

 little way along the branches after the medullary sheath has ceased. By repeated 



z 2 



