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332

Cunningham Memoirs.

the u total length of the hemisphere measured by the tape along its superior
border," * and regarding that as 100, then the relative—i. e. percentage
length of the fissure—according to him, is as follows for the different
ages :—

Full-term foetus, .... 32*8
First year, . . ., . 35*8

4 to 5 years, .... 33*9

11 to 15 years, .... 36*1
Adult, . . . . .39-3

Hence, for any given age, the length of the fissure can be fairly accurately
estimated, and employed to control the preceding plan.

Kohler recognized that the most important extremity of the fissure of
Rolando is the lower one. He employed for the determination of this an
instrument constructed as follows:—A sagittal iron band is laid over the
medium plane of the head, and so fixed that it lies over the root of the
nose in front and the occipital protuberance behind; two rods which are
to mark the vertical lines suggested by Reid are fixed into small collars
which slide in a slot in the central band. A rod which is to mark the
situation of the fissure of Rolando is hinged at its upper end to the sagittal
band, and it slides in a spring slot on the anterior vertical rod, so that it can
take any position and direction. In applying this instrument the central
band is first laid on the head in the usual way, and then the anterior
vertical rod is pushed backwards until its lower end lies in the preauricular
fossa. The second vertical is similarly pushed backwards parallel with the
first until it strikes the posterior border of the mastoid process, if the
upper end of the rod is placed at a point which is 55'5 per cent, of the
total length of the naso-occipital distance.

In this way Kohler, while apparently modifying Reid's method, really
employs a procedure very similar to that described on page 324. He, of
course by relying on the mesial plane as a starting basis, secures sufficient

* The obvious error will be clue to the measurement of the hemisphere being too large unless
the thickness of the scalp and skull is eliminated.