432 



THE TISSUES. 



Fig- 278. 



ter precede the former. The development of the peripheral extre- 

 mities of the nerve-fibres is also peculiar, and requires a distinct 

 consideration. 



1. The nerve-fibres in the nerve-trunks, except their peripheral 

 terminations, are developed in their positions, from primordial, 

 fusiform, nucleated cells, conjoined into pale, flattened, nucleated 

 tubules, T2 i?ny to 4 Au f an i nc h broad. (Fig. 277.) In this state 

 they are gray, or dull white ; but in the embryo at the 4th to the 



5th month, they assume a 

 white color, and the me- 

 dulla continues to be more 

 and more developed in 

 them, and thus they be- 

 come dark-bordered fibres. 

 Thus the axis-fibre ap- 

 pears to be developed 

 from the central portion 

 of the contents of the ori- 

 ginal tubule, while the 

 external portions undergo 

 a sort of fatty metamor- 

 phosis into the medulla. 



2. The development of 

 the peripheral terminations 

 of the nerve-fibres, has 

 been investigated satis- 

 factorily only in the tail 

 of the tadpole. The pale 

 nucleated tubules describ- 

 ed under the preceding 

 head, here and there anas- 

 tomose, and terminate in 

 free fibrils of the finest 

 kind, eotfoo to -5VV OCF f 

 an inch in diameter. 

 These are evidently form- 

 Nerves from the tail of a tadpole. 1. Embryonic nerve- ed from the Coalescence of 

 fibres in which more than one dark-bordered tube has been n-n O.ITJ. Un- 



developed. 2. Similar fibres containing but one tube, which 



in one fibre ceases at (&). 3. Embryonic pale fibres; 4, fusi- and Continue tO be pushed 

 form cells connected together, and with a complete nerve- ., , , ~, -, 



fibr e._Magnified 350 diameters. (KottiJcer.) further by Offsets towards 



