THE STRUCTURE OF THE ELEMENTARY TISSUES. 



97 



large fibres, as they approach both their central and their peripheral 

 end, lose their medullary sheath and assume many of the other charac- 

 ters of the fine fibres of the sympathetic system, it is not necessary to 

 suppose that there is any material difference in the two kinds of fibres. 

 The non-medulla ted fibres frequently branch. 



- It is worthy of note that in the foetus, at an early period of develop- 

 ment, all nerve-fibres are non-medullated. 



Nerve-trunks. Each nerve-trunk is composed of a variable num- 

 ber of diiferent-sized bundles (funiculi) of nerve-fibres which have a 

 special sheath (perineurium). The funiculi are inclosed in a firm fibrous 

 sheath (epineurium)', this sheath also sends in processes of connective 



Fig. 102. Small branch of a muscular nerve of the frog, near its termination, showing divisions 

 of the fibres, a, into two; 6, into three, x 350. (Kolliker.) 



tissue which connect the bundles together. In the funiculi between the 

 fibres is a delicate supporting tissue (the endoneurium). 



There are numerous lymph-spaces both beneath the connective tissue 

 investing individual nerve-fibres and also beneath that which surrounds 

 the funiculi. 



Every nerve-fibre in its course proceeds uninterruptedly from its 

 origin in a nerve-centre to near its destination, whether this be the 

 periphery of the body, another nervous centre, or the same centre whence 

 it issued. 



Bundles of fibres run together in the nerve-trunk, but merely lie in 

 apposition to each other; they do not unite: even when they anas- 

 tomose, there is no union of fibres, but only an interchange of fibres 

 between the anastomosing funiculi. Although each nerve-fibre is thus 

 7 



