In creating a
movable joint for the head, then, a safe passage had to be obtained for
the medulla--that part of the great nerve stem which joins the brain to
the spinal cord. The medulla is part of the brain stem.
This was only one of the difficulties which had to be overcome. The eyes
are set on the pre-fulcral lever of the head. For our safety we must be
able to look in all directions--over this shoulder or that. We must also
be able to turn our heads so that our ears may discover in which
direction a sound is reaching us. In fashioning a fulcral joint for the
head, then, two different objects had to be secured: free mobility for
the head, and a safe transit for the medullary part of the brain stem.
How well these objects have been attained is known to all of us, for we
can move our heads in the freest manner and suffer no damage whatsoever.
Indeed, so strong and perfect is the joint that damage to it is one of
the most uncommon accidents of life.
Let us see, then, how this triumph in engineering has been secured.
Pages:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25