NERVE VESICLES. 263 



Nerve fibres terminate in various ways. Their ends may tliin out and 

 become free, or they may form a loop, and so return back in Manner of 

 their course. Each nerve runs in an unbroken line from its termination of 

 origin to its termination, but between the adjacent ones in- 

 tercommunication is established by the formation of plexuses. On the 

 other hand, as the fibres are preparing to enter the nervous centres, the 

 membranous tube dilates so as to receive a nerve vesicle, Manner of re _ 

 with which the diaphanous axis cylinder is thus brought in ceptionofvesi- 

 contact. Where corpuscles are received into the membran- cles ' 

 ous sheath, it is not always certain but that the fibre has some other 

 termination beyond. Some have supposed that sensitive fibres differ 

 from the motor ones in the circumstance that the former alone are 

 brought in connection with the corpuscles, but this is very unKkely. 



Second. The vesicular nervous substance is composed of nucleated 

 cells containing a granular substance, with which there are The vesicular 

 intermixed, especially near the nuclei, pigment granules. P rtion - 

 These granules, however, are sometimes absent, as in the vertebrata. 

 The nucleus of each ganglionic vesicle often presents a nucleolus ; the 

 diameter of the vesicle varies from -g-J^ to 1 2 * 5 Q of an inch. These ves- 

 icles are found in the nerve centres, their coloring material communicat- 

 ing to those parts the peculiar tint they display. In shape they vary 

 very much, some being spherical, some ovoid, and others caudate, ex- 

 hibiting processes which are filled with granules, or which, becoming 

 eventually transparent, communicate with similar processes from other 

 cells, or are continuous with the axis cylinders of the nerve-tubes. Ac- 

 cording to Axmann, the axis cylinder is a continuation of the nucleus 

 of the cell. The ganglion vesicles, as they are termed, are character- 

 Fi 116 ized by containing a large amount of phosphor- 



ized oil, and it is probable that the oxidation of 

 this material is a condition of their functional ac- 

 tivity. 



Fig. 116, ganglion globules (nerve-cells), from 

 the Gasserian ganglion of the cat. 1. Cell, with 

 short pale process, showing the origin of a fibre ; 

 <z, sheath of the cell and nerve-tube, containing nu- 

 clei ; b, cell membrane of the nerve-cell. 2. Cell, 

 with the origin of a fibre without sheath ; b, cell 

 membrane of the nerve-cell. 3. Nerve-cell, de- 

 prived, in the preparation of it, of its membrane 

 Nerve W magnified awdi- and external sheath. (Kolliker.) 



Fig. 117, p. 264, bipolar nerve-cell of the pike, 



continued at each end into nerve-tubes, a, sheath of the nerve-cell ; b, 

 sheath of the nerve ; c, medulla ; d, axis cylinder continuous with the 



