( 405 ) 



and 9^'' no longer the lO'^' derniatouui (sec lig'. I and II, left side). 



After cutting throngli the 9^'' ]-0()t (see fig. Ill to the left) we like- 

 wise may observe tliese two areas ; hy cutting ilirough the 8"i root 

 no lateral insensible area is produced, at the utmost a ver^- small 

 one at Ihe mid-ventral line. 



The isolation of the 9^'' dermatoma (see fig. Ill to I ho right) 

 shows, that the stretching has had a very strong effect on it. Neither 

 ventrally nor dorsally it has retained any longer any connection with 

 the mid-vcnti'al and mid-dorsal lines, and only by projections shaped 

 pointwise the direction of this lost connection is indicated. 



But this does not pro\e that this sensible area is the whole of the 

 dermatoma. Only its lateral portion is isolated there. Dorsal and 

 ventral portion have dwindled away to insignificant pieces with 

 a minimum sensory \alue, rapidly fallijig beneath the threshold. 

 Isolation of the 9^'' dermatoma together with the lO*^'' (see fig. Y) 

 produces however a very large dorsal area, and by cutting through 

 the 9^'' root a very small ventral spot is still produced. 



Much more probable than that it should pass as a whole on the 

 extremity, it is therefore that the 9^'^ dermatoma, like the 10 'S sends 

 only its lateral part on the caudal half of the extremity, whilst it 

 still possesses a xery small ventral spot (as may be shown by 

 cutting through the root), perhaps even a still less important dorsal 

 spot (that may be found by isolating the root together with one of 

 the neighbouring ones, the 10 ''^ or the 6"^'^). 



But the 7^'! and eight dermatoma too, that have wholly lost the 

 dorsal piece (see fig. IV to the right), send only their lateral pieces 

 on the extremity. In cases where one ventral side has been made 

 wholly insensible, if the 8^'^ root on the other side is cut through, 

 the consequence will e\'en be a small outward curve passing beyond 

 the mid-ventral line. But the 7^^^ and the 8"' dermatoma overlap 

 one another completely. If the 8^'' root is cut through, there is found 

 no lateral insensible area on the hand. 



In short, the innervation of the extremity is provided for exclu- 

 sively b}- the lateral parts of the dermatomata. Their ventral and 

 dorsal parts become gradually smaller, and are at last (in as much 

 as concerns the 7''' and 8^') wholly or almost wholly lost. 



Thus it has become possible to survey in a simple form the man- 

 ner in which the extremity makes use of the lateral parts of the 

 dermatoma. 



A cone of the extremity growing in caudal direction, a lateral 

 growth, meets on its way the lateral parts of the dermatomata (at 



