1406 ON CUTANEOUS AND [BOOK m. 



structure of which throws light on that of the kinds just men- 

 tioned. 



The end-bulbs are found not in the skin generally but in 

 certain situations only, namely the conjunctiva and the lips, and 

 a special form occurs in the sensitive surfaces of the genital 

 organs. They are not confined to the outer surface of the body, 

 but are found also in mucous membranes, in the tongue and 

 palate, in the rectum and elsewhere. 



An end-bulb is a small rounded or oval body, 30 p to 100 ^ 

 in diameter, consisting of a capsule of connective tissue enclosing 

 a core of peculiar material. The capsule is indistinctly fibrillated, 

 and bears nuclei which are sometimes so arranged as to indicate 

 an outer capsule with nuclei placed* lengthwise to the longer axis 

 of the bulb, and an inner capsule with nuclei placed crosswise. 

 The core consists of an homogeneous ground substance in which 

 are imbedded granules, or in some cases nuclei ; in some instances 

 the core appears to be made up of small nucleated cells. A 

 medullated fibre, with its neurilemma and sheath of Henle, ap- 

 proaches the end-bulb, and frequently becoming much coiled 

 close to the bulb, plunges into the bulb at its base or side. 

 The sheath of Henle, and perhaps the neurilemma also, become 

 continuous with the capsule ; the axis cylinder covered with 

 medulla passes into the core, and here, frequently coiling about 

 and at times dividing, loses the medulla, and ends in the midst 

 of the core in a blunt slightly swollen end, or when it divides, in 

 more than one such knob. Sometimes more fibres than one end 

 in the same end-bulb. The marked feature of an end-bulb is a 

 special development of the connective tissue wrappings of a 

 nerve fibre, in the midst of which the axis-cylinder, with or 

 without previous division, ends abruptly. The nature of the 

 "core" is at present uncertain; it has been regarded as a modifi- 

 cation of connective tissue but presents some analogies with the 

 medulla of a nerve fibre. 



870. Pacinian corpuscles. Though these are relatively large 

 bodies, often more than a millimeter in length and easily seen 

 by the naked eye, their general plan of structure is similar to that 

 of an end-bulb ; they may be regarded as very large highly 

 developed end-bulbs. 



The axis of the Pacinian corpuscle is furnished by a core, 

 cylindrical or rather an elongated oval in form, resembling that of 

 an end-bulb in that it consists of a homogeneous ground substance 

 to which occur granules or small nuclei ; in structures very similar 

 in Pacinian bodies occurring as in the beaks of some birds (duck), 

 called " Herbst's corpuscles," the core is distinctly composed of nu- 

 cleated cells. This core is surrounded not by a single capsule only, 

 but by a large number, twenty to sixty, of concentric capsules which 

 are crowded together towards the axis but wider apart in the 

 more superficial regions. A longitudinal or transverse section of a 



