342 



MANUAL OF HISTOLOGY. 



the ends of nerves with tissues at the periphery, such as the muscle 

 fibres which, as far as we know at present, have had their origin from the 

 middle germinal plate, is a great theoretical difficulty. 



The usual but unsatisfactory view which is held regarding ganglion 

 corpuscles is that they are metamorphosed formative cells. 



By the enlargement of these, and their subsequent acquisition of a 

 characteristic finely granular contents, the ganglion cell is arrived at. 

 When their further growth takes place regularly we have the apolar 

 element, and the structure with processes when the former is unequal. 

 Through these latter adjacent cells may be connected, and from them 

 nerve fibres are given off. It is possible that multiplication by segmen- 

 tation may take place in already formed nerve cells in the foetal body, 

 but the subject requires closer investigation. 



The formation of nerve fibres, which has been already touched on in 

 the general part of our work (p. 100), was formerly supposed generally to 

 be brought about by the fusion of cells in such a way that (in the case of 

 the non-ramifying nerve tube) connection took place between the indivi- 

 duals of a series of fusiform or cylindrical elements. 



The nervous trunks of man and the mammalia have not that white 

 appearance in early foatal life which characterises them at a later date ; 



they are on the contrary grey 

 and translucent, the more so the 

 younger the embryo. At first 

 we only remark on teazing them 

 out the individual formative 

 cells of fusiform, or simply elon- 

 gated figure, and with vesicular 

 nuclei. Later on we may suc- 

 ceed in splitting off rows of these 

 from the main structure in the 

 form of pale fine nucleated 

 "bands. These are the first nerve 

 fibres whose pale non-medul- 

 lated appearance reminds us of 

 Remak's elements ; their me- 

 dium breadth is '002 9-0 '005 6 

 mm. 



In the older nerves we may 

 perceive the specific contents of 

 the primitive tubes, advancing 

 gradually from the central to- 

 wards the peripheral portions, 

 the axis cylinder arising in all 

 probability first, and the fatty 

 medullary mass being deposited 

 subsequently between it, and 

 the primitive sheath formed of 

 the membranes of the cells. 



These, then, are the usual 

 views on the subject based upon 

 Schwann's outlines, which have 



Fig. 324. Development of nerve fibres; from the tail 

 of a tadpole. 1. A pale siill non-medullated fibre 

 flii ^ *T K " UCleL 2 ' More adva ced tubes partly 

 filled with medullary matter, a, a fibre, with which 

 * stellate formative cell (ai) is connected at its side, 

 while lower down, where the fatty contents gradually 

 give way to a paler (a*), Its division into two branches 



( pM a ?M a4) A2 * fibre wllich i8 united to two 8tellate 

 -ells (6i and 6). 3. A nerve tube srill more developed, 

 at a, the stem at 6, and c, the branches. 



been received into histology. 



The formation of branches on nerve fibres was supposed to take place 



