44 PHYSIOLOGY OF THE HUMAN BODY. 
a membrane, called the pertostewm. The long, roundish bones of the legs 
and arms have this peculiarity, that they are hollow in the middle, and 
are filled with a soft, fatty substance, called marrow. 
The skeleton is divided into the head, the trunk, and the extremities. 
1. The Head.—The bony framework of the head, called the skull, is 
divided into two parts, the cranium and the face. THe Cranium? is 
the shell which contains the brain, and is composed of eight bones, of 
which the following six form its top and sides: the frontal or coronal bone, 
so called from Latin corona, a crown, because it forms the crown of the head, 
marked 1 on fig. 41 ; the two 
parietal bones, so called from 
Latin paries, a wall, because 
they form the walls or sides 
of the head, of which only 
one, marked 2, is seen in the 
figure ; the occipital bone, 
from Latin occiput, the back 
part of the head, marked 
3; the two temporal bones, 
from Latin tempus, temporis, » 
the temple, marked 4. The 
base is formed by other two, 
the sphenord, marked 5, and 
the ethmoid, not visible in the 
figure. The sphenoid, from 
Fig. 41. Greek sphén, a wedge, is 80 
called because it wedges in 
and locks together all the bones of the head and face, being attached to 
fourteen distinct bones ; and the ethmoid, from Greek éthmos, a sieve, 
*Trom its being ae with a large Ses of holes, for the passage of 
nerves from the brain to the face, a of blood-vessels into the brain. It 
will be observed that the bony plates forming the upper part of the 
craninm are joined by ragged edges. These joinings are an elaborate 
system of dove-tailing, pinay together the different pieces as firmly as 
“24 the whole were one, V miele certain purposes are also served by the 
cranium consisting of separate pieces. At the sides of the skull, some of 
the bones sedan each other, those above being supported we those 
beneath. Altogether, the bones of the skull form an arched or vaulted © 
covering of extraordinary strength for the protection of the brain. 
THE Face is made up of fourteen bones, all of which, except the lower 
jawbone, are immovably fixed to each other, and to the bones of the 

1 From Greek perz, about, and os, a bone. 
2 Latin cranium, Greek kranion, from kara, the head. 
