Freiburger historische Bestände - digital

340

Cunningham Memoirs.

to the squamous suture, both of which can easily be felt in the entire head
{vide Introduction). The indices obtained were as follows:—

Age.

Sagittal Preecen-
tral Index.



1-7 years, ....

44





7-16 years, ....

48



- Sagittal squamosal length = 100.

16-106 years,

54





There is no reason to suppose that the superior prsecentral sulcus has
aught but a constant relation to the rest of the hemisphere, and the above-
stated results are doubtless chiefly due to the well-known upward growth
of the squamous suture line (vide p. 143).

The position of the sulcus, so far as its relations to the fissure of Rolando
and the coronal suture are concerned, will be given under the sulcus
frontalis superior.

Sulcus Frontalis Medius.—This small and very subordinate sulcus, which
is often present as a mere branch of the inferior prsecentral, is nevertheless
in an important situation, topographically speaking, since it tends to limit
anteriorly the representation of the upper limb, and since it borders the
area which, on certain data (these, however, being clinical, are very
imperfect), is credited with being the so-called graphic centre (7. e. for
writing). As a matter of fact, excitation experiments in the lower apes
show distinctly that this is the area for extension of the wrist, and other
movements essential to the function of writing.

Topographically, this small sulcus is also important as lying in the
same level as the inferior genu of the fissure of Rolando.

Projected on the exterior of the skull, this sulcus lies midway between
the points the topography of which has just been described, viz. the upper
end of the vertical stem of the inferior prascentral and the lower end of the
superior prsecentral.

No difficulty, therefore, attends its determination, and when fixed it
will assist in localizing the region of the inferior genu.