134 
DE. J. CLELAND OX THE VARIATIONS OE THE HUMAN SKULL. 
proportional length of the chord approaches very near to that of the arc, so that the 
amount of curvature in the three regions in these nations is nearly equal. The Chinese 
skull from the Edinburgh Collection is an exception to this statement; but the calcula- 
tions made from Lucae’s drawings agree completely one with another (p. 123). This 
same phenomenon of near correspondence of the proportional lengths of the chords with 
the lengths of the arcs of the different parts of the arch is a marked characteristic of the 
skulls of infants ; we have therefore here another interesting cliild-like peculiarity of the 
Chinese skulls. Both the Peruvian skulls present the peculiarity of having the parietal 
region distinctly more curved than either the frontal or occipital, and in this they agree 
with the compressed and flattened American skulls ; but how far the peculiarity is refer- 
able to the slight compression which the Peruvian skulls have both to a certain extent 
undergone is an open question. It may be interesting to note that measurements taken 
from the cast of the Tartar skull described by Professor Huxley* as an example of ex- 
treme brachycephalism give 93 and 111 as the proportions of the occipital and frontal 
arcs to the parietal estimated at 100, and 92 and 112 as the proportions of the occipital 
and frontal chords, thus indicating an equally distributed curvature. Eolichocephalism 
and brachycephalism will be treated of in a subsequent page ; meanwhile the writer 
may be allowed to state, without further explanation, that he believes this equally dis- 
tributed curvature to be a brachycephalic characteristic. 
A further and more detailed acquaintance with the curves of the arch may be sought 
by examining the angles formed by lines passing from point to point ; and this will be 
now attempted. 
Angles expressive of the form of different parts of the arch (General Table, columns 
10 to 24). Young skulls . — In the foetus and in infants the forehead springs at a consi- 
derably greater angle from the roof of the orbit than in the adult. Whereas the average 
orbito-frontal angle varies in different nationalities from 77° to 83°, and only one adult 
skull (46) has an orbito-frontal angle exceeding 90°, in the foetal skulls and those of 
infants the same angle exceeds 90° in all except two instances, and in one infant it even 
reaches 104°. In childhood it suffers a little diminution, but principally it gets smaller 
at a later age, when also the orbit is deepened and the frontal sinus enlarged by the 
growth forwards of the upper part of the face, as will be subsequently shown. Thus 
also the orbito-frontal angle is generally larger in females than in males. 
The frontal bone, in the progress of development, changes its curve not only where its 
orbital and frontal plates meet, but also in the course of its frontal plate ; for the mid- 
frontal angle appears to get smaller in the passage from foetal or infantile life to child- 
hood, and again enlarges in the passage to the adult state ; or, in other words, the bone 
becomes more curved in childhood and is again flattened in subsequent growth. In the 
four-months’ foetus the midfrontal angle is of an average adult size, in the two five-months’ 
foetuses it is decidedly smaller, in the seven-months’ foetus it is again larger, and in the 
eight-months’ foetuses it is of a size which would be very flat in the adult. These varia- 
* Loc. cit. 
