PHYSIOLOGICAL ANATOMY OF THE NERVOUS TISSUE. 



573 



throughout the cutaneous surface. There are, also, terminal filaments not connected 

 with any special organs, some of them, perhaps, ending simply in free extremities, and 

 some connected with epithelium. There is still considerable difference of opinion 

 among anatomists concerning all of these various points, but, with regard to the terminal 

 corpuscles, these differences are purely anatomical, and they do not materially affect our 

 ideas of the physiology of sensation. We do not propose, therefore, to enter fully into the 

 discussions upon these questions, and we shall simply present what seem to be the most 

 reasonable views of the latest and most reliable observers. 



Corpuscles of Pacini, or of Vater. These corpuscles, which were the first discovered 

 and described in connection with the sensitive nerves, were called corpuscles of Pacini, 

 until it was shown that they had been seen about a century and a half ago by Vater. 

 Their actual mode of connection with the nerves, however, has only been ascertained 

 within the last few years. The following are the measurements of these bodies and the 

 situations in which they are found, taken from Kolliker : 



In man, these corpuscles are oval or egg-shaped and measure from $ to | of an inch 

 in length. They are always found in the subcutaneous layer on the palms of the hands 

 and the soles of the feet, and are most numerous on the palmar surfaces of the fingers 

 and toes, particularly the third phalanges. In the entire hand there are about six hun- 

 dred, and about the same number on the feet. They are sometimes, but not constantly, 

 found in the following situations : The dorsal surfaces of the hands and feet, on the 

 cutaneous nerves of the arm, the forearm and the neck, the internal pudic nerve, the 

 intercostal nerves, all of the articular nerves of the extremities, the nerves beneath the 

 mammary glands, the nerves of the nipples, and in the substance of 

 the muscles of the hands and feet. They are found without excep- 

 tion on all of the great plexuses of the sympathetic system, in front 

 of and by the sides of the abdominal aorta, and behind the peri- 

 toneum, particularly in the vicinity of the pancreas. They some- 

 times exist in the mesentery and have been observed near the 

 coccygeal gland. 



The structure of the corpuscles consists simply of several layers 

 of connective tissue enclosing a central bulb in which is found 

 the terminal extremity of the nerve. This bulb is finely granu- 

 lar, nucleated, and is regarded by most anatomists as composed 

 of connective tissue. At the base of the corpuscle, is a pedicle 

 formed of connective tissue surrounding a medullated nerve-fibre 

 which penetrates the corpuscle and terminates in the central bulb. 



The only really important point of discussion with reference to 

 the structure of the nerve-fibre in the central bulb, and this is 

 purely anatomical, is whether or not the medullary substance ex- 

 tend into the corpuscle itself. Probably the fibre is here reduced 

 simply to the axis- cylinder. All anatomists agree that a single 

 thin, flat fibre penetrates the corpuscle and terminates near its 

 summit by a slightly - enlarged and granular extremity. The 

 arrangement of the different anatomical elements is shown in 

 Fig. 178. 



The situation of these corpuscles beneath, instead of in the 

 substance of the true skin, shows that they cannot be properly 

 considered as tactile corpuscles, a name which is applied to other 

 structures situated in the papillae of the corium ; and it is impos- 

 sible to assign to them any special function connected with sen- 

 sation, such as the sense of temperature, or the appreciation of 



pressure or weight. All that we can say with regard to them is that they constitute 

 one of the several modes of termination of the nerves of general sensibility. 



FIG. 178. Pacinian cor- 

 puscles. (Sappey.) 



1, base of the corpuscle; 2, 

 apex ; 3, 3, 8, substance 

 of the corpuscle, in lay- 

 ers ; 4, 4, nerve pene- 

 trating the corpuscle; 

 6, cavity of the corpus- 

 cle ; (>, nerve ; 7, nerve, 

 which has lost its me- 

 dullary substance and 

 sheath ; 8, termination 

 of the nerve ; 9, pranu- 

 lar substance continuous 

 with the nerve. 



