THE NERVOUS SYSTEM. 169 



however, in their course, very frequent anastomoses, in which 

 way the various larger and smaller plexuses with decussating 



fibres are formed. The formation of these plexuses is due to 

 an interchange of entire fasciculi or fibres, never to a connec- 

 tion between the individual primitive fibres, and in a micro- 

 scopical point of view affords no point worthy of remark. 



Divisions of the nerve-fibres do not occur, according to our 

 present experience, in the trunks and larger branches of the 

 spinal nerves of the Mammalia [in Fishes, Stannius noticed 

 numerous divisions in the trunks of the motor and mixed 

 nerves ('Archiv fur phys./ Heilk. 1850, p. 77)], nor do they 

 exhibit any considerable change in their diameter; but in 

 the ultimate ramifications, on the other hand, it is certain 

 that such divisions do take place, even in Man, accompanied 

 by a very considerable diminution in the size of the fibres ; with 

 respect to which conditions, and the terminations in the skin, 

 muscles, bones, and membranes in general, reference may be 

 made to the detailed descriptions given in the proper places. 



One kind, only, of termination of the spinal nerves, is 

 still to be noticed here, — that in the- Pacinian bodies. The 

 small bodies, so named by Henle and myself (' Ueber die 

 Pacin. KOrperchen des Menschen und der Thiere/ Zurich, 

 1844), were first accurately described by the Italian, Pacini 

 ('Nuovi organi scoperti nel corpo umano/ Pistoja, 1810), 

 especially in the nerves of the palm of the hand and sole 

 of the foot, and, in fact, as Langer of Vienna afterwards 

 showed, had been previously noticed by A. Vater (J. G-. 

 Lehmann, ' Be consensu partium corp. hum./ Vitembergse, 

 1741), although their nature had not been recognised. These 

 organs are of an elliptical or pyriform shape, of a whitish 

 transparent colour, with whiter streaks internally, and measure 

 i — 2'" in size ; in Man, they are constantly found on the 

 cutaneous nerves of the palm of the hand and sole of the 

 foot, in the subcutaneous connective tissue itself, and most 

 numerously in the fingers and toes, particularly on the third 

 phalanx, — according to Ilerbst (' Die Pacin. Korpcrchcn und 

 ihre Bedeutung/ Gott., 1847) there are about GOO in the hand 

 and not quite so many in the foot ; besides which, it must here 

 also be stated, that they are invariably found on the great sympa- 

 thetic plexus, in front of, and close to the abdominal aorta, 



