176 SPINAL GANGLIA. [BOOK i. 



inner side are smaller. A quantity of connective tissue carrying 

 blood vessels and lymphatics runs between the groups and passing 

 into each group runs between the cells and fibres; and a thick 

 wrapping of connective tissue continuous with the sheath of the 

 nerve surrounds and forms a sheath for the whole ganglion. 



Each of the nerve cells, ganglionic cells as they are called, 

 examined under a higher power, either after having been isolated 

 or in an adequately thin and prepared section, will present the 

 following features. 



The cell consists of a cell-body which is, normally, pear-shaped, 

 having a broad end in which is placed the nucleus and a narrow 

 end which thins out into a stalk and is eventually continued 

 on as a nerve fibre. The substance of the cell-body is of the kind 

 which we call finely granular protoplasm ; sometimes there is an 

 appearance of fibrillation, the fibrillse passing in various direc- 

 tions in the body of the cell and being gathered together in a 

 longitudinal direction in the stalk. Sometimes the cell-body 

 immediately around the nucleus appears of a different grain from 

 that nearer the stalk, and not unfrequently near the nucleus is an 

 aggregation of discrete pigment granules imbedded in the proto- 

 plasm. The several cells of the same ganglion frequently differ as 

 to the appearances of the cell-body, this being in some more 

 distinctly or coarsely granular than in others, and also staining 

 differently. 



The nucleus, like the nuclei of nearly all nerve cells, is large 

 and conspicuous, and when in a normal condition is remarkably 

 clear and refractive, though it appears to consist like other nuclei 

 of a nuclear membrane and network and nuclear interstitial ma- 

 terial. Even more conspicuous perhaps is a very large spherical 

 highly refractive nucleolus ; occasionally more than one nucleolus 

 is present. 



Surrounding the cell-body is a distinct sheath or capsule con- 

 sisting of a transparent, hyaline, or faintly fibrillated membrane, 

 lined on the inside by one layer or by two layers of flat, polygonal, 

 nucleated epithelioid cells or plates ; that is to say, cells which 

 resemble epithelium cells, but differ not only in being extremely 

 flattened, but also in the cell body being transformed from 

 ordinary granular protoplasm into a more transparent differen- 

 tiated material. In stained specimens the nuclei of these plates 

 are very conspicuous. Under normal conditions this sheath is 

 in close contact with the whole body of the cell, but in hardened 

 and prepared specimens the cell body is sometimes seen shrunk 

 away from the sheath, leaving a space between them. Occasionally 

 the cell body while remaining attached to the sheath at three 

 or four or more points is retracted elsewhere, and accordingly 

 assumes a more or less stellate form ; but this artificial condition 

 must not be confounded with the natural branched form which as 

 we shall see other kinds of nerve cells possess. 



