NERVE COLLATERALS 69 



they are grayer than the medullated nerves. The non-medullated fibers 

 frequently branch. 



It is worthy of note that in the fetus, at an early period of development, 

 all nerve fibers are non-medullated. 



Nerve Trunks. Each nerve trunk is composed of a variable number 

 of different-sized bundles, funiculi, of nerve fibers which have a special 

 sheath, perineurium. The funiculi are enclosed in a firm fibrous sheath, 

 epineurium; this sheath also sends in processes of connective tissue which 

 connect the bundles together. In the funiculi between the fibers is a delicate 

 supporting tissue, the endoneurium. There are numerous lymph spaces 

 both beneath the connective tissue investing individual nerve fibers and 

 also beneath that which surrounds the funiculi. 



FIG. 90. Terminal Ramifications of a Collateral Branch Belonging to a Fiber of the 

 Posterior Column in the Lumbar Cord of an Embryo Calf. 



Bundles of fibers run together in the nerve trunk, but they merely lie 

 in approximation to each other, they do not unite. Even when nerves anas- 

 tomose, there is no union of fibers, but only an interchange of fibers between 

 the anastomosing bundles. Although each nerve fiber is thus single through 

 most of its course, yet, as it approaches the region in which it terminates, it 

 may break up into several subdivisions before its final ending. 



Nerve Collaterals. It has been discovered through the researches of 

 Golgi, and confirmed by the further studies of Cajal and other anatomists, 



