( 311 ) 
This is not quite accurate. The analgetic area situated most 
caudally is always a little broader than that situated cranially, 
whilst the sensible area is midling in breadth between those two. 
Many more or less important deviations from this rule may occur 
besides"); it may safely be stated however that, proceeding carefully, 
the analgetic areas will always be much narrower than double, 
and much broader than half the breadth of the sensible area. 
In most cases their relation is such that, taking the sensible area 
for unit, the analgetic area situated cranially is from 0,8—1,1, and 
the one situated caudally from 1,1—1,4. 
Consequently the breadth of the sensible area towards the mid- 
dorsal line is nearly equal to that of each analgetic area, though 
the latter represents two sectionned roots, the former only one root 
left intact. 
These two facts: 
Ist. One sectioned root does not cause analgesy towards the 
mid-dorsal line. 
2nd, One root left intact commands a central area, which towards 
the mid-dorsal line is nearly as broad, as each analgetic area 
(dependent on two sectioned roots) is towards that region, 
may teach us something about the manner in which the derm- 
atomata are ranged on the mid-dorsal line. 
Since the researches of SHERRINGTON it is known that the derma- 
tomata overlap one another in antero-posterior direction, it is known 
too that these overlappings must be rather important, but the two 
facts mentioned above, connected with the facts already previously 
communicated, teach us something more about them. 
If, notwithstanding the lesion of the root on which it is depen- 
dent, the central area preserves a considerable breadth towards the 
mid-dorsal line, the marginal areas cannot be very broad towards 
that region. During the whole of the following demonstration the 
lawful supposition has been taken for granted, that towards the 
mid-dorsal line each marginal area can be equivalent at the utmost 
to half of the central area only. 
This supposition needs not to be proved here, and it simplifies 
all calculations in a most important way. 
1) As to the trunkdermatomata, situated cranially and influenced by the growth 
the upper extremity, or caudally and influenced by that of the lower extremity, the 
conditions are very much more complicated, 
21* 
