i6o 



HISTOLOGY 



Tendon Spindles. Tendons possess free sensory endings, together 

 with the tendon spindles. These are small portions of the tendon, 1-3 

 mm. long and 0.17-0.25 mm. wide, enclosed in sheaths of connective 

 tissue. They stain more deeply than the surrounding tendon. 



The few nerve fibers which terminate in a tendon spindle lose their 

 sheaths and branch freely, ending in club-shaped enlargements (Figs. 149 

 and 150). They are found in all tendons and serve to transmit the sensa- 

 tion of tension, being active in connection with coordinated movements. 

 In connective tissue the sensory nerves may have free endings. In 

 addition to these the subcutaneous tissue near the coils of the sweat 



glands, and in the corium of the fingers 

 and toes, sometimes contains terminal 

 cylinders (of Ruffini) which resemble 

 tendon spindles in the way that their 

 nerves ramify (Fig. 151). These cylin- 

 ders lack the distinct capsules which 

 characterize the nerve corpuscles. 



PIG. 153. GENITAL CORPUSCLE FROM THE 

 HUMAN GLANS PENIS. METHYLENE 

 BLUE STAIN. (After Dogiel, from Bdhtn 

 and von Davidoff.) 



FIG. 154. BULBOUS CORPUSCLE FROM THE HUMAN CON- 

 JUNCTIVA. METHYLENE BLUE STAIN. (After Dogiel, 

 ' from B6hm and von Davidoff.) 



Terminal' corpuscles are nerve endings consisting of a coarse nerve 

 fiber, or knot of small branches, surrounded by a semifluid intercellular 

 substance (which is granular in preserved tissue), and enclosed in a con- 

 nective tissue capsule. The terminal ramifications of the nerve show 

 irregular swellings or varicosities, and apparently they unite so as to make 

 a network. Often more than one fiber enters a corpuscle, and it has been 

 suggested that they include afferent and efferent fibers. Generally the 

 connective tissue sheaths of the entering fibers blend with the capsule, 

 and the myelin sheaths are lost just within it. Terminal corpuscles have 

 been grouped as tactile, genital, bulbous, articular, cylindrical, and lamellar. 



Tactile corpuscles (or Meissner's corpuscles) are elliptical structures, 

 40-100 n long and 30-60 n broad (Fig. 152). They are characterized 

 by transverse markings, due to the corresponding elongation of the capsule 

 cells and the tactile cells within. From one to five medullated fibers 

 enter the lower end of a tactile corpuscle, losing their sheaths soon after 

 entering. They pursue a spiral course through the corpuscle, giving off 



