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CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



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. 



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, 

 that each individual nerve fiber in the central nervous system gives off in its 



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

 Column in the Lumbar Cord of an Embryo Calf. 



course branches which pass out from it at right angles for a short distance, 

 and then may run in various directions. These branches are called collaterals. 

 They end in fine, brush-like terminations known as end-brushes, or in little 

 bulbous swellings which come in close contact with some nerve cell, figure 90. 

 In the nerve-centers, that is, in the brain and spinal cord, the different 



