104 



NERVOUS SYSTEM. 



Fig. 28. 



Ganglion Corpuscles. After Valentin 

 In one a second nucleus is visible 



Fig. 29. 



Histologists are generally of opinion, that the central portion of each 

 nerve-fibre differs from the peripheral : the former has been termed by 

 Rosenthal and Purkinje the axis- cy Under ; the latter is the medullary 

 or white substance of Schwann, and to it the white colour of the cere- 

 bro-spinal nerves is chiefly due. 



The researches of histologists have shown that vesicles or cells 



containing nuclei and nucleoli, and called 

 also nerve corpuscles and globules and gan- 

 glion corpuscles and globules, are the essen- 

 tial elements of gray or vesicular matter. 

 These are found in the nervous centres, 

 mingled with nerve-fibres, and imbedded in 

 a dimly shaded or granular substance. 

 They give to the ganglia and to certain 

 parts of the brain and spinal cord the pecu- 

 liar grayish or reddish-gray appearance by 

 which they are characterized. They are 

 large nucleated cells, filled with a finely 

 ?wonSoi S i fseveralcontain80neor granular material; some of which is often 



dark, like pigment ; the nucleus, which is 

 vesicular, containing a nu- 

 cleolus. The marginal figure 

 (Fig. 28) represents some 

 that have a regular outline. 

 Others, as in Fig. 29, are cau- 

 date or stellate, and have tu- 

 bular processes issuing from 

 them, filled with the same 

 kind of granular matter as 

 is contained in the corpuscle. 

 The gray substance is not 

 always at the exterior, nor 

 the medullary in the interior. 

 In the medulla spinalis, their 

 situation is the reverse of 

 what it is in the brain. In 

 the invertebrata, the gray 

 matter forms the nuclei of 

 the ganglia, which are the 

 centres of the nervous sys- 

 tem ; and the true spinal 



Stellate or Caudate Nerve Corpuscles. After Hannover. System, which Occupies the 



a, . From the deeper part of the gray matter of the con- interior of the Spinal COrd, 



volutions of the cerebellum. The larger processes are di- J^S ]j een regarded aS a chain 

 rected towards the surface of the organ, o. Another trom . . , 



the cerebellum, c, d. Others from the post-horn of gray ol Similar ganglia. It IS tne 

 matter of the dorsal region of the cord. These contain pig- alrparlv sVlOWTl of 



ment, which surrounds the nucleus in c. In all the speci- Organ, aS already SnOWn, O 



mens the processes are more or less broken. Magnified 200 ,1 PXcitO-mOtOrV nerVOUS 



diameters. -f . , 



function. Kuyscn consider- 

 ed, that the gray portion owes its colour to the blood-vessels that enter 



