GENERAL PHYSIOLOGY OF NERVE-TISSUE. 



107 



high magnification the axis presents a longitudinal striation, indicating 

 a fibrillar structure. The fibrillae appear to be embedded in an 

 intervening semifluid substance, the neuroplasm. 



Non-medullated Nerve-fibers. These consist, for the most 

 part, only of the axis-cylinder, though in some portions of the nervous 

 system a neurilemma is also present. Though much less abundant 

 than the former variety, tney are distributed largely throughout the 

 nervous system, but arejgarticularly abundant in the sympathetic. 

 Owing to the absence of a medulla,"" tney present ~a ramerpSfe'b'r 

 grayish appearance. 



structure of Nerve-trunks. After their emergence from the 

 brain and spinal cord, the nerve-fibers become bound together, by 



FIG. 44. TRANSVERSE SECTION or A NERVE (MEDIAN), ep. Epineurium. 

 Perineurium. ed. Endoneurium. 



pc. 



connective tissue, into the form of continuous bundles, which connect 

 the brain and cord with all the remaining structures of the body. 

 The bundles are technically known as nerve-trunks or nerves. Each 

 nerve is invested by a thick layer of lamellated connective tissue, 

 known as the ejgn^yz&m. A transverse section of a nerve shows 

 (see Fig. 44) that it is made up of a number of small bundles of 

 fibers, each of which possesses a separate investment of connective 

 tissue the perineurium. Within this membrane the nerve-fibers are 

 supported by"T fine stroma the endoneurium. After pursuing a 

 longer or shorter course, the nerve-trunk gives off branches, which 

 interlace very freely with neighboring branches, forming plexuses, 

 the fibers of which are distributed to associated organs and regions 



