The Affebent and Efferent Neubons 67 



Tactile corpuscles [Fig. 50] occur in some of the papillae of the skin 

 of the hand and foot, and more sparingly in the back of the hand, the 

 inner surface of the forearm, the lips, eyelids, nipples, and external genital 

 organs. End bulbs (other than the genital corpuscles) are often very 

 small, but sometimes are over 50/* in diameter. Genital corpuscles are 

 from 20 fi to 350/". in diameter. 



Tactile corpuscles are always within the connective tissue layer of the 

 skin, the corium [Fig. 51]. They are from 80/* to 150^ in length, and 

 Ys as broad. 



End bulbs [Fig. 52] are found in the conjunctiva, in the corium in or 

 below the papillae of the lips and tongue, in serous membrane, in tendons, 

 aponeuroses, the epineurium of nerve trunks, in the neighborhood of the 

 joints and in the corium of the modified skin covering the external genital 

 organs. 



Pacinian corpuscles ( Vater-Pacinian corpuscles: Golgi-Mazzonni cor- 

 puscles) are larger than end bulbs, and formed with many concentric 

 layers of connective tissue, like the layers of an onion. A single medullated 

 nerve fibre enters the corpuscle, losing its medullary sheath and branching 

 within [Fig. 53]. 



Pacinian corpuscles are found principally in the subcutaneous tissues, 

 especially of the hands and feet; in the periosteum of some bones; in the 

 neighborhood of tendons and ligaments and in the connective tissues within 

 the abdomen. They are relatively large, being sometimes 1.5 mm. in length. 



TENDON AND MUSCLE SPINDLES. 



A special form of ending, the organ of Golgi, is found in the tendons 

 near the point of attachment of muscle fibers. The tendon bundle here 

 becomes enlarged, and splits into a number (8 to 20) of smaller fasciculi. 

 One or more nerve fibers penetrate between these fasciculi, losing their 

 medullary sheathes, and arborizing there [Fig. 54]. The whole enlarge- 

 ment is enclosed in a connective tissue capsule continuous with the areolar 

 tissue between the tendon bundles. Tendon spindles are from 1 to 1.5 mm. 

 in length. 



A somewhat similar mode of termination occurs in the muscle spindle. 

 This consists of a connective-tissue sheath enclosing a bundle of from two 

 to twenty or more muscle fibers (an ' intrafusal bundle ') which are smaller 

 than the surrounding fibers and more like embryonic fibers. The sub- 

 divisions of some of the nerve fibers which enter the spindle wrap them- 

 selves spirally about the muscle fibers. The branches of others terminate 

 in plate-like expansions applied to the fibers [Fig. 55]. 



