THE SPINAL NERVES. 



179 



The sheath contains nerve-cells and ^^S- ii9- 



fibres, and sends in a few fine processes to 

 support these structui'es. The fibres of 

 the posterior root enter and pass out of 

 the sranfflion without suffering" anv 

 chang-es, except that the nerve fibres are 

 slightly separated by the presence of a 

 few nerve-cells, and that a distinct in- 

 crease in the number of nerve fibres takes 

 place. The nerve-cells, of which the 

 g-ang-lion is chiefly composed, and upon 

 the number of which its size directly de- 

 pends, are arranged chiefly around the 

 fibres of the dorsal root ; such few as 

 lie between the fibres are smaller than 

 the rest and vary more in their relative 

 numbers ; at times one or two isolated 

 cells are found in the capsule or even in 

 the adjoining ' periganglionic gland/ 

 The cells near the capsule are somewhat 

 smaller than the deeper cells ^. Each of 

 these cells, which are usually pear-shaped, 

 possesses only one process ; the cell mem- 

 brane is thick, resistant, and possessed of 



an external nucleated, endothelial covering, the space around 

 being probably a pericellular lymph-space ; it often contains one to 

 three small fat-globules ; the protoplasm 

 of these has, according to v. Lenhossek, 

 a concentric fibrillation ; the nucleus is 

 round, clear, and distinct, and relatively 

 larger the smaller the nerve-cell ; it is 

 usually placed in the centre of the cell. 



In that portion of the cell towards the 

 process is a portion brighter and less 

 easily stained than the rest of the cell 

 (Polarkernen, Courvoisier); this apparent- 

 ly possesses one or two nuclei, and is 

 regarded as a cell by Lenhossek (Polar- 

 zellen); the process of each cell soon 

 acquires a medullated sheath, and after 



' Larger cells of deeper layer 80 /i to 90 /x in diameter, sometimes one or two as 

 large as o-i mm. v. Lenhossek. 



y 2 



Ventral view of the spinal ganglia ; 

 on the rlglit side they are still 

 hidden by the 'periganglionic 

 glands. ' 



¥is. 120. 



Schema of spinal ganglion. 



A Ventral root. 



' ' Ramus commiinicaus. 



G Ganglion. 



Dorsal division. 



P Dorsal root. 



J{ \'entral division. 



