76 GENERAL ANATOMY. 



In the case of motor or efferent nerve-fibres the deep origin is in cells contained 

 within the spinal cord or brain, the axis-cyliuder processes of these cells being 

 prolonged to form the fibres. In the case of the sensory nerves the origin is 

 somewhat different, inasmuch as they arise from the cells of ganglia situated 

 externally to the central nervous system. The sensory fibres of a spinal nerve 

 arise, for instance, from the cells of the ganglion of the posterior root ; these 

 cells give off a process which branches in a T-shaped manner (Fig. 46, B), one 

 of the limbs of the T extending peripherally, while the other passes inwards 

 and penetrates the spinal cord. In connection with the sensory cranial nerves, 

 origins are described imbedded within the substance of the brain ; these are not, 

 however, the proper origins, but are groups of cells around which the fibres, 

 growing inwards form the ganglion-cells, situated just outside the brain, end, 

 and from which new fibres arise, which pass upwards in the substance of the 

 brain. 



Peripheral Terminations of Nerves. The manner in which nerve-fibres ter- 

 minate peripherally are several, and may be conveniently studied in the sensory 

 and motor nerves respectively. Sensory nerves would appear to terminate either 

 in minute primitive fibrillse or networks of these ; or else in special terminal organs, 

 which have been termed peripheral end-organs, and of which there are three 

 principal varieties viz. the end-bulbs of Krause, the tactile corpuscles of Wagner, 

 and the Pacinian corpuscles. 



Termination in Fibrillse. When a medullated nerve-fibre approaches its termi- 

 nation, the white matter of Schwann suddenly disappears, leaving only the axis- 

 cylinder surrounded by the neurilemma, and we have now a non-medullated 

 fibre. This undergoes repeated division, and after a time loses its neurilemma, 

 and consists only of an axis-cylinder, which can be seen, in preparations stained 

 Avith chloride of gold, to be made up of fine varicose fibrils. Finally, the axis- 

 cylinder breaks up into its constituent primitive nerve-fibrillse, which anastomose 

 with one another, thus forming a network, and often present regular varicosities. 

 This network passes between the elements of the tissue to which the nerves are 

 distributed, which is always epithelial, and the nerve-fibrils end in the interstitial 

 substance between the epithelial cells, or, as is believed by some, actually ter- 

 minate within the cells as minute swellings close to the nucleus. In this \\i\\ 

 nerve-fibres have been found to terminate in the epithelium of the skin and 

 mucous membranes, and in the anterior epithelium of the cornea. 



The end-bulbs of Krause (Fig. 52) are minute oblong or cylindrical corpuscles, 

 into the interior of Avhich the axis-cylinder of the nerve-fibre passes, and termi- 

 nates in a coiled, plexiform mass or in a bulbous extremity. The corpuscle con- 

 sists of a simple nucleated capsule, containing a soft, homogeneous core, in which 

 the termination of the axis-cylinder is contained. The white matter of Schwann 

 ceases abruptly as the axis-cylinder enters the corpuscle, but the neurilemma is 

 continued inward with the axis-cylinder, and forms an investment of the core, 

 lining the interior of the capsule. The end-bulbs have been described as occurring 

 in the conjunctiva (where, in man, they are spheroidal in shape), in the mucous 

 membrane of the mouth, and in the cutis and mucous membrane of the penis, 

 clitoris, and vagina, where they are termed genital corpuscles. The latter have a 

 mulberry-like appearance, from being constricted by connective-tissue septa into 

 from two to six knob-like masses. In the synovial membrane of certain joints 

 (e. g. those of the fingers) rounded or oval end-bulbs have been found ; these are 

 designated articular end-bulbs. 



The tactile corpuscles (Fig 53), described by Wagner and Meissner, are oval- 

 shaped bodies, made up of connective tissue, and consisting of a capsule, and 

 imperfect membranous septa, derived from it, which penetrate its interior. The 

 axis-cylinders, entering the capsule, pursue a convoluted course, supported by the 

 septa, and terminate in small globular or pyriform enlargements, near the inner 

 surface of the capsule. These tactile corpuscles have been described as occurring 

 in the papillae of the corium of the hand and foot, the front of the fore-arm, the 



