The
Mastoid Portion.
The
superior border is thin, bevelled at the expense of the internal surface, so as
.to overlap the lower border of the parietal bone, forming the squamous
suture.
The
position and size of this foramen are very variable. It is not always present;
sometimes it is situated in the occipital bone or in the suture between the
temporal and the occipital. The mastoid portion is continued below into a
conical projection, the mastoid process, the size and form of which vary
somewhat. This process serves for the attachment of the Sterno-mastoid, ~Jllenius
capitis, and 'rl'achelo-mastoid muscles. On the inner side of the mastoid
process is a deep groove, the digastric fossa, for the attachment of the
Diga"tric muscle; and, running parallel with it, but more internal, the occipital
gronee. which lodges the occipital artery.
