2 4 8 



NERVOUS SYSTEM. 



[SECT. 120. 



Pig. 103. 



der Thieve. Zurich. 1844.) after Professor Pacini, of Pisa, are of 

 an elliptical or pyriforai shape, of a transparent whitish colour, 

 with a whiter streak in the interior, and of §'" to 2'" in size. In 

 man, they are constantly found upon the cutaneous nerves of the 

 palm of the hand and sole of the foot, seated in the subcutaneous 



tissue, and most numerously in the 

 fingers and toes, especially in the 

 third phalanges. In exceptional 

 cases, they occur also upon other 

 spinal nerves; and it may here, 

 moreover, be stated, that they are 

 invariably to be found on the 

 branches of the large sympathetic 

 plexus before and alongside the ab- 

 dominal aorta, behind the peri- 

 toneum, especially in the neighbour- 

 hood of the pancreas; often, also, 

 in the nerves in the mesentery, 

 nearly as far out as the intestine. 

 The structure of the Pacinian bo- 

 dies is, upon the whole, simple (fig. 

 103). Each consists of very many 

 (20 to 60) concentric layers of a 

 somewhat homogeneous connective 

 tissue, with numerous delicate plasm- 

 cells. The outer layers are separated 

 by larger, the inner by smaller in- 

 terspaces, containing a clear serous 

 fluid, whilst the cavity of the inner- 

 most layer is filled with a clear, 

 finely granular substance furnished 

 with delicate nuclei. Each body 

 has a roundish pedicle, formed by 

 the continuation of its membranous 

 layers. This is connected with 



—e 



A human Pacinian body, magnified 3o0 

 times, a. Tedicle of the same ; b. nerve- 

 fibre in it: c. outer, d. inner layers of 

 the envelope ; e. pale nerve-fibre in the 

 central cavity ;/. division and termina- 

 tion of the same. 



a 



nerve-twig, and contains a dark 

 nerve-fibre, 0006'" to o'oGS'" broad, running into the Pacinian body. 

 The fibre passes from the pedicle into the central cavity, is 

 here reduced to o , oo6" / in breadth, and o , oo4" / in thickness, 

 becomes pale, non-medullated, almost like the axis-cylinder of 

 a nerve-fibre, and terminates in the upper part of the central 

 cavity by a free, slightly granular knob, the extremity being 



