SECT. 120.] 



NERVOUS SYSTEM. 



249 



frequently bifid or trificl. These bodies occur in great numbers 

 in many mammalia (most beautifully in the mesentery of the 

 cat), and also in birds, in the skin, extremities, beak, and 

 tongue (Herbst, Will) ; but their physiological import is as yet 

 altogether obscure. Further information, including zootomical 

 details respecting them, may be found in Herbst, Die Pacin- 

 ischen Korperchen, Gottingen, 1847 > Bowman, Art. Pacinian 

 Bodies, in Cycl. of Anat. ; and several papors quoted in my 

 Micr. Anat. 



The spinal nerves, at their exit from the dura mater, are en- 

 veloped by a firm covering of connective tissue, the nerve-sheath, 

 neurilemma, which also enters into the interior of the nerves with 

 fine processes, and, as in the muscles, Pig- 104. 



marks off larger and smaller fasciculi, 

 and also penetrates, in form of deli- 

 cate septa, between the individual tubes 

 (fig. 104). In the terminal ramifica- 

 tions, where single fibres, or collec- 

 tions of a few fibres, still frequently 

 possess an external sheath, the neuri- 

 lemma appears as a homogeneous en- 

 velope beset with elongated nuclei, of 

 0"003'" in diameter ; and in this form 

 it is found also in the smaller branches of the cutaneous and 

 muscular nerves, only that the substance there begins gradually to 

 split up into longitudinal fibres, the nuclei lengthen out to from 

 6 , oo5" / to o'Oo8'", often almost as in smooth muscles, and plasm-cells 

 aud elastic fibrils appear, which latter often encircle whole bundles. 

 Finally, in the larger nerves, ordinary connective tissue, with 

 distinct longitudinal fibrils, as in fibrous membranes, intermingled 

 with a network of elastic fibres, makes its appearance, yet even 

 here, particularly in the interior, there occur immature forms of 

 connective and elastic tissue. 



All the larger nerves contain vessels, although not in great 

 numbers, running principally in the longitudinal direction, and 

 forming a loose network of fine capillaries, of 0-002'" to o , oo4'", 

 with elongated meshes, which invests the bundles, and, in part, 

 enters between the elements of them, yet never surrounds the 

 individual primitive fibres, but always collections of them. The 

 ganglia contain beautiful reticular capillaries in the form of a 

 raeshwork, each ganglion-globule being surrounded by special 

 vessels. The Pacinian bodies also contain vessels, which penetrate 



Transverse, section of the nervw 

 ischiadicus ; magnified 15 times. 

 a. General investments of the 

 nerve ; b. neurilemma of the ter- 

 tiary bundles ; c. secondary nerve- 

 bundles, in part with special 

 sheaths. From the calf. 



