60 GENERAL ANATOMY. 



(fibres of Eemak). These consist of a bundle of finely granular fibrillae, in- 

 closed in a sheath. Nuclei may be detected at intervals in each fibre, which 

 Schultze believes to be situated in the sheath of the nerve. In external ap- 

 pearance the gelatinous nerves are semi-transparent, and gray or yellowish- 

 gray. The individual fibres va-ry in size most of them being of smaller size 

 than in the cerebro-spinal nerves, so that the average size of the latter is given 

 at 2TrW to -sn'on of an inch, and of the former at only half that size; but on the 

 one hand the smallest fibrils of the cerebro-spinal system are, as we have seen, 

 of hardly appreciable thickness; while on the other some of the gelatinous 

 fibres (especially those in the olfactory bulb), are said to be three or four times 

 as thick as those of the cerebro-spinal nerves. 



Chemical composition. The following analysis, by Lassaigne, represents the 

 relative proportion of the different constituents composing the gray and white 

 matter of the brain. 



Gray. White. 



Water 85.2 73.0 



Albuminous matter 7.5 9.9 



Colorless fat 1.0 13.9 



Bed fat 3.7 0.9 



Osmazome and lactates 1.4 1.0 



Phosphates . 1.2 1.3 



100.0 100.0 



It appears from this analysis, that the cerebral substance consists of albumen' 

 dissolved in water, combined with fatty matters and salts. The fatty matters, 

 according to Fremy, consist of cerebric acid, which is most abundant, choleste- 

 rin, oleophosphoric acid, and olein, margarin, and traces of their acids. The 

 same analyst states, that the fat contained in the brain is confined almost ex- 

 clusively to the white substance, and that its color becomes lost when the fatty 

 matters are removed. According to Vauquelin, the cord contains a larger pro- 

 portion of fat than the brain; and, according to L'Heritier, the nerves contain 

 more albumen and more soft fat than the brain. 



With regard to the constitution of the different portions of the nervous sys- 

 tem, the cerebro-spinal axis is composed of the two above-described kinds of 

 nervous structure, intermingled in various proportions, and having in the brain 

 a very intricate arrangement, which can only be fully understood by a careful 

 study of the details of its descriptive anatomy in the sequel. The gray or 

 vesicular nervous matter is found partly on the surface of the brain, forming 

 the convolutions of the cerebrum, which are in the most direct relation to the 

 mental faculties, and the lamina of the cerebellum, the functions of which are 

 still a matter of dispute. Again, gray matter is found in the interior of the 

 brain, collected into large and distinct masses or ganglionic bodies, such as the 

 corpus striaturn, optic thalamus, and corpora quadrigemina; the functions of 

 which bodies, so far as they have been ascertained, have been found to be con- 

 nected with some of the main organic endowments of the body, such as volun- 

 tary motion, sensation, sight. Finally, gray matter is found intermingled inti- 

 mately with the white, and without definite arrangement, as in the corpora 

 dentata of the medulla and cerebellum, or the gray matter in the pons and the 

 floor of the fourth ventricle. Such scattered masses of gray matter are, in 

 many instances at any rate, connected to all appearance with the origin of par- 

 ticular nerves. In other situations their use is as yet unknown. 



The proper nervous matter, both in the brain and spinal cord, is traversed 

 and supported by a network of fine connective tissue. This has been termed 

 by Virchow the neuroglia, and is supposed to be the source of one of the forms 

 of tumor recently described by that author under the name of glioma. 



The white matter of the brain is divisible into four distinct classes of fibres. 

 There are, in the first place, the nerves which arise in the gray matter, and pass 

 out through the cranial foramina. Next the fibres which connect the brain 



