94 



TEXT-BOOK OF PHYSIOLOGY. 



In the glands, taking as an illustration the parotid and mammary glands, 

 the nerve-fibers, also derived from sympathetic or peripheral neurons, pass 

 into the body of the gland and ultimately reach the acini, on the outer surface 

 of which they ramify and form a plexus. From this plexus fine fibers pene- 



SenFory 

 nerve-fiber.. 



Muscle 

 fibers. 



Motor plate. 



Nerve-fiber 

 bundle. 



FIG. 46. MOTOR NERVE-ENDINGS OF INTERCOSTAL MUSCLE-FIBERS OF A RABBIT. 



X 150. (Stohr.) 



trate the acinus wall and end on the gland-cell. The fibers present a varicose 

 appearance (Fig. 47). 



The afferent nerves as they approach their ultimate terminations 

 undergo similar changes. The end-tufts become associated, in some situ- 

 ations, with specialized end-organs which are extremely complex. 



In the skin and mucous membranes the mode of termination varies con- 

 siderably. The following are some of the principal modes: 



1. Free endings in the epithelium. 



2. Tactile cells of Merkel. 



3. Tactile corpuscles in the papillae of 



the true skin. 



4. Pacinian corpuscles found attached to 



the nerves of the hands and feet, to 

 the intercostal nerves, and to nerves 



B 



FIG. 47. TERMINATIONS OF NERVE- 

 FIBERS IN THE GLAND-CELLS. A. Cell 

 of the parotid gland of a rabbit. B. 

 Cells of the mammary gland of a cat in 

 gestation. (Doyon and Moral.} 



in other situations. 



5. End-bulbs of Krause in the conjunc- 

 tiva, clitoris, penis, etc. 

 (A consideration of these end-organs 



will be found in the chapters devoted to the organs of which they form 

 a part.) 



In the skeletal muscles afferent fibers become associated with small 

 spindle-shaped structures known as muscle-spindles or neuromuscle end- 

 organs. These spindles vary in length from i mm. to 4 mm. They consist 

 of a capsule of fibrous tissue containing from five to twenty muscle-fibers. 

 After penetrating the several layers of the capsule, the nerve-fibers lose the 

 neurilemma and myelin sheaths. The axons or axis-cylinders then divide 



