88 
THOMPSON YATES LABORATORIES REPORT 
As just mentioned, the topography of certain skin-areas of painfuhiess and hyperalgesia, 
explicable by reference from visceral disease, has been investigated by Head, and shown by him to 
exhibit a segmental arrangement. This segmental scheme is, broadly taken, notably similar to 
that of the spinal root-fields as exhibited in Macacus. For instance, the areas of reference 
observe like the root-fields the great mid-dorsal and mid-ventral lines of the limb described above ; 
a point of difference is that the former are individually less extensive, and therefore exhibit less 
overlapping than the latter. The difficulty of minute comparison betv\^een the tw^o is much 
enhanced by the frequent individual variation which I find obtain. 
One noteworthy point issues clearly from their comparison, however. In the root-fields 
I met certain peculiarities of contour which recurred with such constancy that I soon came to 
recognise them as diagnostic for certain fields. These bold peaks and notches are obvious also in 
the visceral areas of Head, e.g.^ the groin peak from the Xllth thoracic, the lateral flap upwards 
from the Vth thoracic, the lateral flap downwards from the Ilird cervical, the axillary peak of the 
Ilnd thoracic. The similarity is too significant for chance coincidence. Again, Head's weighty 
discovery that two fields of skin — an upper between IVth cervical and 1st thoracic, and a lower 
between 1st lumbar and Vth lumbar — are, as regards reference of visceral pains, virgin and blank, 
suffices of itself to establish the intimate connection of the two schemes. The situation of these 
gaps is, according to both sets of observations, the very region of most pure, of least complicated, 
limb character. Exact and absolute correspondence between skin-fields of Macacus and Man is not 
to be expected, if, as I have, I think, proved above, the skin and muscles of Man are more pre- 
fixed than are those of Macacus. 
