728 PHYSIOLOGY. 



Tactile Corpuscles. The student well knows that in the epithe- 

 lium of the skin and mucous membranes the nerves of common sen- 

 sation are arranged, for the most part, in networks of fibrillae. In 

 addition to these there are other special terminal organs of sensory 

 nerves. These are variously known as tactile corpuscles. These are 

 concerned in the perception of some special quality or quantity of 

 sensory impulses. They have their site, not in the surface of the 

 epidermis, but deeper within the tissues. The principal ones among 

 them are the corpuscles of Pacini, the end-bulbs of Krause, the cor- 

 puscles of Meissner t and the corpuscles of Merkel. 



The tactile corpuscles of Meissner in the papilla of the cutis 

 vera are oval bodies 1 / 30 of an inch in length and nearly the same 

 width. These are the corpuscles of the palm of the hand and sole 

 of the foot. One or two medullated nerve-fibers are spirally twisted 



Fig. 296. Cutaneous Papillae Deprived of Their Epidermis and the 

 Vessels Injected. (LANDOIS.) 



a, a, a, Tactile papillae, each containing a Meissner corpuscle. 



around it, and near the top of the corpuscles the nerves lose their 

 Avhite substance and the axis-cylinders end in flat bodies penetrating 

 the surface of the corpuscle. The corpuscle is composed of flattened 

 cells, which give it a striated appearance. These corpuscles are built 

 up of a great number of tactile discs and of tactile cells. There are 

 about twenty tactile corpuscles to a square millimeter of the skin. 



The Pacinian or Vater's corpuscles are attached in greatest num- 

 ber along the digital nerves of the fingers and toes and occasionally 

 on other nerves. These bodies are oval or pyriform, about one- 

 eighth of an inch in length and one-twelfth of an inch in thickness. 

 They have a pearly luster and consist of a series of capsules or con- 

 centric layers of fibrous tissue, with here and there a nucleus. The 

 outer capsules are separated more widely than the inner ones and 

 the interspaces are filled with a colorless liquid. Each corpuscle is 

 attached to a nerve by a pedicle of fibrous tissue through which 



