The Afferent and Efferent Neurons 



61 



All these ascending and descending branches send lateral branches into 

 the gray matter of the cord, as do the fibers of the other bundle. 



The dendrites of some of the T-cells probably pass from the nerve over 

 the white ramus communicans to the sympathetic and collateral ganglia ; 

 whether these fibers continue without interruption through the ganglia to 

 the visceral tissues, or whether they are relayed, receiving stimulations 

 from cells in the sympathetic or collateral ganglia, does not seem clearly 

 made out. The other dendrites pass out over the spinal nerves to termin- 

 ations in skin, subcutaneous tissues, muscle and tendon, and are properly 

 called somatic afferent neurons. 



AFFERENT NERVE ENDINGS. 



The dendrites of afferent neurons end in four ways: 1. 'free'; 2. in 

 contact with specially adapted epithelial cells ; 3. in special structures or 

 ' end organs ' of connective tissue, ' encapsulated endings ' ; and 4. the 

 dendrite in certain cases is modified, forming a characteristic end organ 

 which is a part of the neuron itself. 



Fig. 46. Tactile discs. Highly magnified. (Ramon y Cajal.) These flat expan- 

 sions of the fibers, containing net-works of fibrils, lie between the cells in epithelial 

 tissues. 



FREE NERVE ENDINGS. 



The fibers are said to end free when there are no specific ' end organs ' 

 in connection with them [Fig. 45]. Free endings are found chiefly in 

 epithelial tissues (skin, mucous membrane, cornea of eye, etc.), although 

 they may be present in other tissues. 



When afferent fibers terminate in the ' free ' way, they usually branch 

 several times in sub-epithelial tissues, and lose first (as we approach the 



