648 NERVOUS SYSTEM. (NERVOUS CENTRES. GREY NERVOUS MATTEK.) 



It is in vain, in the present state of our 

 knowledge, to speculate upon the use of these 

 caudate processes. Do they constitute a bond 

 of union between the nerve-vesicles and certain 

 nerve-tubes? or are they comraissural fibres 

 serving to connect the grey substance of different 

 portions of the nervous centres ? Until a more 

 extended research has made us better acquainted 

 with the peculiarities of these vesicles in various 

 localities, it would be premature to offer any 

 conjecture concerning their precise relation to 

 the other elements of the nervous centres. They 

 exist, with different degrees of developement, 

 in the locus niger of the crus cerebri, in the 

 laminae of the cerebellum, in the grey matter 

 of the spinal cord and medulla oblongata, and 

 in the ganglions, and in the grey substance of 

 the cerebral convolutions, in which latter situa- 

 tion they are generally of small size. 



When a portion of grey matter from a con- 

 volution of the brain is examined with a high 

 power in the microscope, we observe it to con- 

 sist chiefly of a mass of granular matter, in 

 which nerve-vesicles are imbedded with consi- 

 derable intervals between them. Henle states, 

 with much truth, that the superficial part of the 

 grey matter of the convolutions seems almost 

 entirely composed of finely granular substance, 

 in which lie, scattered here and there, several 

 clear vesicles which, as he remarks, look almost 

 like openings (fig. 372). In the middle por- 

 tion the vesicles appear larger, and the gra- 

 nular matter becomes less abundant, and on 

 the most deep-seated plane the nerve-vesicles 

 are much increased in size and lie in closer 

 juxtaposition, being, however, covered by a 

 thin layer of granular matter, which forms a 

 sheath to each vesicle. Nerve-tubes are found 

 throughout the whole depth of the grey matter. 

 Those in the most superficial layer are ex- 

 tremely fine and varicose, and seem to corre- 

 spond in number and situation to the vesicles. 

 For wherever there is a nerve-vesicle, we find an 

 extremely fine varicose nerve-tube apparently 

 adherent to it. 



Fig. 372. 



Grey substance from the surface of the cerebral hemi- 

 spliere of a full-grown rabbit treated with dilute 

 acetic acid. (After Henle.} 



a, nerve-vesicle ; b, a similar one with two nu- 

 clei ; c, another viewed along its edge ; d, vesicles 

 indistinctly apparent ; e, granular matter. 



In the grey matter of the ganglions we find 

 that the vesicles are also deposited in granular 

 matter, which surrounds each of them as a 

 sheath (fig. 371, f, g), completely investing it 



on every side, and separating it from the neigh- 

 bouring ones. Here, however, the sheath is 

 formed not only of a finely granular matter, but 

 also of numerous bodies which resemble nuclei 

 or cytoblasts, and this sheath invests both the 

 globular variety of nerve-vesicles and the cau- 

 date ones. Nerve-tubes lie in immediate con- 

 nexion with these vesicles, and sometimes en- 

 twine themselves around them, and seem to 

 indent their sheaths (Jig. 375.) 



Other vesicles, much more simple in form, are 

 found in the grey matter in certain situations. 

 The outer layer of the optic thalamus, accord- 

 ing to Henle, contains only small homoge- 

 neous globules, analogous to the nuclei of the 

 ganglionic globules, in immediate apposition 

 with each other, and towards which the tubes 

 seem to ascend in the vertical direction. Pur- 

 kinje states, that a similar layer is met with in 

 the cortical substance of the brain quite close 

 to the medullary substance.* I find a layer 

 of similar particles in the grey matter of the 

 cerebellic lamina 1 . And, according to the 

 report of Valentin,f Purkinje has found the 

 interior of the ventricles in the normal state 

 covered by an oily matter, which consists 

 of distinct, large, transparent globules, free 

 and lying near each other. A similar layer 

 has been found by him in the interior of the 

 fifth ventricle. The cavity of the rhomboidal 

 sinus in Birds likewise contains a gelatinous 

 mass, which consists of large globules lying 

 close to each other. J 



Developement of grey matter. In the per- 

 fect nerve-vesiclej the cell form of primitive 

 developement is persistent. We have the nu- 

 cleolus and nucleus (cytoblast) and the cell ; 

 and, according to Schwann, the only change 

 which the full-grown cell exhibits consists in an 

 increase of size and in the developement of the 

 pigmentary granules within. The following is 

 Valentin's description of the developement of a 

 nerve-vesicle. In the very young embryos of 

 Mammalia, as the sheep or calf, the cerebral 

 mass in the course of formation contains, in the 

 midst of a liquid and transparent blastema, 

 transparent cells, with a reddish yellow nucleus. 

 The wall of the cells is very thin and simple ; 

 their contents are colourless, transparent, ho- 

 mogeneous, and manifestly liquid ; the nucleus, 

 with well-defined contour, is generally round, 

 sometimes central, at other times excentric, 

 solid, and nearly of the same colour as the 

 corpuscles of the blood. Around these primi- 

 tive cells of the central nervous system, which 

 we find likewise formed after the same type in 

 the spinal cord, a finely granular mass becomes 

 deposited, which probably is not at first sur- 

 rounded by an enveloping cell-membrane. At 

 this early period of formation the primitive cell 

 still preserves its first delicacy to such a degree 

 that the action of water causes it to burst im- 

 mediately. This rupture of its membrane and 

 effusion of its contents often take place so sud- 

 denly and quickly that they can be perceived 



* Henle, loc. cit. t Uber den Verlauf, &c. 



f See further remarks on the grey matter in the 

 account of the minute structure of the brain aud 

 spinal cord in a subsequent part of the article. 



