150 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



probable that two muscles which are commonly associated in 

 co-ordinate movements are innervated by the same root, even 

 though they may be supplied by different nerves. 



The interchange of fibres which makes this possible takes 

 place partly in the plexus (cervical, lumbar, etc.) and partly in 

 the larger nerve-trunks, which are themselves to be regarded as 

 a sort of plexus. 



Only few cases of disease of the spinal ganglia are known. Besides acute 

 pain, an intercostal herpes zoster extending along the course of the affected 

 nerves has been taken as a symptom of this trouble. It is questionable, however, 

 whether this should be referred to the ganglionic apparatus, for we have herpes 

 zoster without disease of the ganglia, and, furthermore, herpes zoster has been 

 found to follow inflammation of the peripheral nerves. 



The roots, therefore, enter the spinal cord along its whole 

 length. The latter becomes somewhat thickened at those points 

 where the largest roots enter it from the extremities. The cer- 



O 



viral enlargement receives the nerves of the arms, and the lumbar 

 enlargement those of the leg. The intercostal nerves arise from 

 the narrowest part of the spinal cord. The lowest, club-shaped, 

 portion is called the conus terminalis : from it there arise not only 

 the nerves but a long, thin prolongation, the filum terminale. 



The upper boundary of the cord is formed by the commence- 

 ment of the decussation of the pyramidal tract (of which, later). 



It is often an important diagnostic point at the bedside to 

 determine the level at which those nerves arise which supply 

 certain paralyzed muscles or anaesthetic regions of the skin. 



The effort has been made to settle this question by experi- 

 ments on animals, for the simple anatomical method would 

 never suffice. The attempt has repeatedly been made to sum- 

 marize those local injuries to the cord in human beings (com- 

 pressions, haemorrhages, etc.) which give rise to definite disturb- 

 ances and utilize the results to settle this question. 



I give you herewith the results attained by Starr in this 

 manner, who made a comparative study of all the cases he could 

 obtain, in 1888. In all probability, further researches will lead 

 to minor corrections. 



