468 



NERVOUS SYSTEM 



membranes the nerves terminate in end-bulbs, or corpuscles of Krause 

 (see Fig. 105, p. 466). In the cornea, branching nerve-fibres pass to 

 the nucleoli of the corneal corpuscles and to the nucleoli of the cells 

 of the posterior layer of epithelium. 



Structure of the Nerve-centres. A peculiar pigmentary matter in the 

 nerve-cells and in the surrounding granular substance gives to the nerve- 

 centres a grayish color, by which they are readily 

 distinguished from the white, or fibrous division 

 of the nervous system. Wherever this gray 

 matter is found, the anatomical elements of the 

 tissue are cellular, except in the nerves formed of 

 gray, or gelatinous fibres. Under the general 

 division of nerve-centres are included, anatomi- 

 cally at least, the gray matter of the cerebro- 

 spinal centres, the ganglia of the roots of the 

 spinal and certain of the cranial nerves, and the 

 ganglia of the sympathetic system. In these 

 parts are found cells, which constitute the essen- 

 tial anatomical element of the tissue, granular 

 matter resembling the contents of the cells, pale 

 fibres originating in prolongations of the cells, 

 elements of connective tissue, delicate membranes 

 enveloping some of the cells, with bloodvessels 

 and lymphatics. 



Nerve-cells. The following varieties of cells 

 exist in the nerve-centres and constitute their 

 essential anatomical elements : unipolar, bipolar 

 and multipolar cells. These cells present great 

 differences in their size and general appearance, 

 and some distinct varieties are found in particular 

 Fig. I07< _ unipolar ceil portions of the nervous system. Unipolar and 

 ^ be Gasserlan s^gHon bipolar cells are found in the ganglia of the 

 N, V N, nuclei of the cranial nerves and in the ganglia of the posterior 

 sheath; T, fibre branching at roots of the spinal nerves. Small unipolar cells 

 are found in the sympathetic ganglia. Multipolar 



cells present three or more prolongations. Small cells, with three and 

 rarely four prolongations, are found in the posterior cornua of the gray 

 matter of the spinal cord. From their situation they have been called 

 sensory cells; and they are found in greatest number in parts known to be 

 endowed exclusively with sensory properties. Large, irregularly-shaped 

 multipolar cells, with a number of poles, or prolongations, are found 

 chiefly in the anterior cornua of the gray matter of the spinal cord, 



