7° 



NERVOUS TISSUE. 



[sect. 31. 



inasmuch as, while they have precisely the aspect of non-medul- 

 lated nerves, they often run to great distances, and, at the same 

 time, ramify variously. How these processes ultimately terminate, 

 whether free or by connection with nerve-fibres, or by anastomoses 

 with similar processes, is not yet made out; but it appears not impro- 

 bable, that all these three possibilities occur in different situations. 



Nerve-fibres and nerve-cells unite to form two substances, very 

 differently constituted in their extremes, the grey and ivhite sub- 

 stance. The latter forms the white medulla, as it is called, or the 



Fig. 29. 



Large nerve-cell, with processes, from the anterior comua of the human spinal cord. 

 Magnified 350 times. 



medullary matter of the spinal cord and brain, and the nerves; 

 and consists essentially of fascicularly arranged or interwoven 

 nerve-tubes, to which, in the peripheral nerves, a special envelope 

 of connective tissue, the neurilemma, as it is called, is superadded. 

 The grey substance chiefly contains nerve-cells, and, in certain 

 places, a finely granular matrix and free nuclei. It very rarely, 

 however, occurs quite pure, but is generally intermingled, more or 

 less, with nerve-tubes. This is especially the case in the majority 

 of the ganglia, in the grey substance of the spinal cord, and in the 

 so-called cerebral ganglia; while, on the other hand, in the grey 

 cortex of the brain and cerebellum, it is, in some places, almost 

 destitute of nerve-fibres. This substance is much more largely 



