160 
DR. J. CLELAND ON THE VARIATIONS OE THE HUMAN SKULL. 
A B C D represents the base, E the post- 
auricular depression, and F the nasal spine ; E' 
represents the position of the postforaminal 
depression when the ear is more elevated above 
the foramen magnum A B, or with a more level 
base A' B' C D. The lines drawn to F' and F" 
show the effects of removal of the nasal spine 
downwards or forwards. The diagram suffices for the geometrical proof of the statements 
which have been made. 
III. POSITION OE THE SKULL ON THE VERTEBRAL COLUMN. 
We are now in a better position to consider the way in which the skull is set on the 
vertebral column than we were at the commencement of the investigation, as various 
points which have emerged with regard to form bear on the question of position. This 
question is the more difficult as it cannot be altogether settled by means of precise me- 
thods, as the position of the body is continually changing. It may, however, be pretty 
safely assumed that in the erect posture the head in the human subject is nearly balanced. 
There can be no doubt, and it is well known, that in the ordinary standing positions the 
whole body is supported by balance, while muscular action is only required to preserve 
that balance. This is seen most distinctly with regard to the lower limbs, for the gas- 
trocnemius and soleus are flaccid in standing, as may be easily proved by observing how 
they become rigid and change their form as soon as an attempt is made to rise on tiptoe ; 
the flaccidity of the quadriceps extensor cruris is proved by the moveability of the patella 
so long as the knee is straight and the foot on the ground ; and that the glutei muscles 
are entirely relaxed in standing is shown by observing how the gluteus maximus at once 
becomes rigid on bending the body forwards, and the gluteus medius and minimus when 
the opposite foot is lifted up. It is not so easy to prove the relaxation of the muscles of 
the back in standing, although the curves of the vertebral column speak distinctly 
enough of balance; but if, with the head held erect and loosely, the fingers of both 
hands be rested on the upper part of the complexus muscles, and flexion be made from 
the hips, without changing the relative positions of head, neck, and trunk one to another, 
those muscles will be felt to swell out and harden, again to relax on resumption of the 
erect posture. It appears to be a general principle of animal statics that the body can 
be supported without muscular action ; and in the human subject the absence of an 
elastic ligamentum nuchae shows that it is not by the principle of suspension that the 
head is preserved erect. 
But if the head be balanced on the vertebral column, it must change its position with 
growth, and be gradually tilted up more and more from childhood to adult life, to 
throw more weight behind the condyles as the frontal and temporo-sphenoidal lobes of 
the brain increase in size, and the face-bones become heavier; and the greater the 
growth of these parts the greater must be the tilting up. This tilting or rotation back- 
