1877.] 



System of the Brain, 



329 



course alone by the line of nuclei running parallel to its wall, and within 

 which the elongated nucleus proper to the vascular coat becomes now 

 and again apparent. 



Identical as these nuclear bodies are in appearance their site pro- 

 bably betokens far different functional endowments appertaining to 

 each, the extravascular being truly connective, whilst those lining the 

 lymphatic channels develop into lymph-corpuscles, and correspond, in 

 fact, to lymphatic endothelia. These connective and endothelial elements 

 having a separate and wholly distinct destiny, also differ inter se in re- 

 lative number and distribution, the connective elements being, in con- 

 ditions of health, a constant element, the endothelial subject to diverse 

 physiological influences, by which their appearance and proportions may 

 be greatly modified. The recognition of these connective and endothelial 

 elements, and the varying conditions imposed upon them by their distinct 

 functional endowments, is of essential importance when we are dealing 

 with the morbid brain. 



Further examination sufficed to prove that this arrangement of nuclei 

 regularly around the nerve-cell in the human subject, in which epilepsy 

 and other morbid affections were present before death, was a condition 

 frequently met with in the lower animals as apparently a perfectly 

 normal state, and the brain of the healthy cat afforded peculiarly favour- 

 able opportunities for studying their distribution and significance. 



Here it was most satisfactorily demonstrated to my mind that the 

 pericellular nuclei were arranged along the boundary of a perfectly clear 

 space. This space completely enclosed the nerve-cell and gradually 

 tapered off and disappeared towards the apex process of the pyramids. 

 The remaining processes (lateral and basal) of the nerve-cell cross the 

 intermediate space, passing through the boundary wall of the enclosing 

 sac, the cell being in reality suspended by its branches within this peri- 

 cellular cavity. The appearance of these spaces will be greatly modified 

 by the method of preparation adopted, the thinness of the section, and 

 various physiological and pathological conditions existing before death. 



On reference to the sketch (Plate 1. fig. 1) which represents the ascend- 

 ing frontal convolution in a young cat, the section being taken from the 

 gyrus immediately in front of the crucial sulcus, we find four nerve-cells 

 surrounded by these clear spaces which, in this case, are widely distended. 

 One of these pericellular sacs also exhibits the arrangement of nuclear 

 elements above alluded to. In most cases the outline of the cell is closely 

 followed by the enclosing sac, and from this cause the form of the peri- 

 cellular sac is subject to great diversity of contour. 



Recent examination of the cerebral cortex in sections cut on the freez- 

 ing microtome has assured me that the nerve-cells of the middle layers 

 of the cortex are subject to no definite rule as regards their form. The 

 pyramidal form was too exclusively supposed by Meynert to be due to the 

 action of hardening agents, and he certainly erred in assuming the 



