332 



CONSTRUCTION OF THE GANGLIA. 



adherent covering of connective tissue : this outward covering sends processes 

 inwards through the interior. A section carried through a ganglion in the direction 

 of the nervous cords connected with it, discloses collections of nerve-cells, between 

 which the nerve-fibres pass (fig. 38G). Each cell is inclosed in a transparent capsule 

 with nuclei upon its inner surface (figs. 36G, 3G7) ; these capsules are continuous 

 with the primitive sheaths of the nerves (M. Schultze). 



Of the relation between the nerve-fibres in a ganglion and the ganglion-cells, it 

 is probable that some fibres may pass through without being connected with the 

 cells, but that every nerve-cell is connected with a fibre or with fibres. In the case 



Fig. 386. LONGITUDINAL SECTION THROUGH THE MIDDLE OF A GANGLION ON THE POSTERIOR ROOT OF 



ONE OF THE SACRAL NERVES OF THE DOG, AS SEEN UNDER A LOW MAGNIFYING POWER. (E. A. S.) 



a, Nerve-root entering the ganglion ; l>, fibres leaving the ganglion to join the mixed spinal nerve ; 

 c, connective tissue coat of the ganglion ; d, principal group of nerve-cells, with fibres passing down from 

 amongst the cells, probably to unite with the longitudinally coursing nerve-fibres by T-shaped junctions 

 (see text). 



of multi-polar cells, such as are found in the sympathetic ganglia (fig. 367), each of 

 the branches of the cell is in all probability continuous with a nerve-fibre, and the 

 same is certainly the case with bipolar cells, at least those in which the two poles are 

 prolonged from opposite extremities of the cell as in the spinal ganglia of fish (fig. 

 370), as well as in the pyriform cells before noticed (see p. 318) in which two 

 processes arise from a part of the cell near one another, and are continued in 



Fig. 387. BIPOLAR CELL FROM SPINAL GANGLION OF A 4 WEEKS' HUMAN EMBRYO (His). 



opposite directions, either at once, or after the one fibre has made two or more 

 spiral coils around the other or straight fibre. Uni-polar cells are found in the 

 spinal ganglia of the higher vertebrates (fig. 366). In them the single nerve-fibre 

 process is observed to divide before long into two fibres (d}, which traced far enough 

 are found to pass in opposite directions toward the ends of the ganglion. Some- 

 times the branches are of equal size, but they are often unequal, one being decidedly 

 smaller than the other. As in all cases of a division of a medullated nerve-fibre, 

 the bifurcation takes place at a node of Ranvier, and this may be the first node 

 from the cell, or the nerve-fibre may pass two or three or more nodes before thus 

 dividing. The cell-process, which usually acquires its medullary sheath very soon 



