GENERAL PHYSIOLOGY OF NERVE-TISSUE. 109 



root; the latter, the posterior or dorsal root A Each dorsal root 

 presents near its union with the ventral root a small ovoid grayish 

 enlargement known as a g^aglJonA^ Both roots previous to entering 

 the cord subdivide into from four to six fasciculi, j | 



A microscopic examination of a cross-section of the spinal cord 

 shows that the fibers of the ventral roots can be traced directly into 

 the body of the nerve-cells in the anterior horns of the gray matter. 

 The fibers of the dorsal roots are not so easily traced, for they diverge 

 in several directions shortly after entering the cord. In their course 

 they give off collateral branches which, in common with the main 

 fiber, end in tufts which become associated with nerve- cells in both 

 the anterior and posterior horns of the gray matter. 



Of the nerves in connection with the base of the brain, some 

 present a similar ganglionic enlargement, and therefore may be re- 

 garded as dorsal nerves, while others may be regarded as ventral 

 nerves. Their relations within the medulla oblongata are similar 

 to those within the spinal cord. 



Efferent and Afferent Nerves. Nerves are channels of com- 

 munication between the brain and spinal cord, on the one hand, and 

 the muscles, glands, blood-vessels, skin, mucous membrane, viscera, 

 etc., on the other. Some of the nerve-fibers serve for the transmission $* 

 of nerve energy from the brain and spinal cord to certain peripheral f 

 organs, and so increase or retard their activities; others serve for the 

 transmission of nerve energy from certain peripheral organs to the 

 brain and spinal cord which gives rise to sensation or other modes of 

 nerve activity. The former are termed efferent or centrifugal, -the 

 latter afferent or centripetal nerves. Experimentally it has been de- 

 termined that the anterior or ventral roots contain all the efferent, 

 fibers, the posterior" or dorsal roots all the afferent fibers. 



IRAL ENDINGS OF NERVES. 



The eff erenTnerves'aslhey approach their ultimate terminations 

 lose both the neurilemma and myelin sheath. The axon or axis- 

 cylinder then divides Into a number" of branches which become 

 directly and intimately associated with tissue-cells. The particular 

 mode of termination varies in different situations. These terminations 

 are generally spoken of as end-organs, terminal organs, or end-tufts. 

 ^ In the skeletal muscle the nerve-fiber loses both neurilemma and 

 myelin sheath at the point where it comes in contact with the muscle- 

 fiber. ^After penetrating the sarcolemma, the axon or axis-cylinder 

 divides into a number of small branches which appear to be embedded 

 in a relatively large mass of sarcoplasm and nuclei, the whole form- 

 ing the so-called "motor plate." Each muscle-fiber possesses one 

 such plate or end-organ in mammalia, several in the frog. 



