CHAPTERS 
« 
each at their back-parts one large fpongey procefs called mammillaris, 
or maftoideus, and from the lower and middle parts of each a procefs 
which joins the ofla malarum, named jugalis or zygomaticus. 
Ofla petrofa lie between the former bones and the occipital bones, or 
are truly portions of the former bones, being never found feparate in ad* 
ult bodies. They have each on their outfidcs one long llender procefs cal¬ 
led ftyliformis, and near the fide of this procefs a foramen, which runs ob¬ 
liquely forwards into the fcull, through which the carotid arteries pafs to 
the brain; thefc are the fixth foramina, and one foramen in the infide of 
the fcull leading to the organs of hearing, which are the feventh fora¬ 
mina. The ridge on the upper parts of each of thefe bones help to keep 
the brain fteady, and are ftrong fupports to the thin and flat parts of the 
fcull, which elfe would be exceeding weak. What remains of this bone 
belongs properly to a difeourfe on the organs of hearing. 
Between the lafl; deferibed bones and the following bone, are two 
large holes, which are the eighth foramina. Through thefe holes pafs the 
eighth pair of nerves and lateral finufes; fometimes they are two on each 
fide, one for the nerve and one for the finus. To thefe we may add an¬ 
other very fmall one on each fide, through which pafs the portiones du- 
rx of the auditory nerves; and fometimes there is another for an artery. 
Os occipitis, (Tab. iv. v. vi. vii.) makes all the back-part of the fcull: It 
is bounded by the fphenoidal, temporal, petrofal, and parietal bones; it 
has two fmall apophyfes, by which it is articulated to the fpine; near thofe 
apophyfes are two fmall foramina, which are the ninth of the fcull; 
through thefe pafs the ninth pair of nerves; and between thefe is the 
great or tenth foramen, through which the medulla oblongata defeends 
into the fpine, the cervical arteries enter, and the cervical veins pa fs out. 
In the infide of this bone is a crucial fpine imprefled by the longitudinal 
and lateral linufes; and on the outfide oppofite to the middle of this fpine, 
in fome bodies, is an apophyfis, and from that down to the great foramen 
a fmall thin fpine. The fpines in this bone are of the fame ufe with thofe 
in the os frontis, &c. viz. to ftrengthen it. The thinner parts of this bone 
are alfo defended J)y the mufcles that cover them; which provifion is very 
neccflary, becaufe we can leaf!: defend this part, and blows here are of 
worfe confequence than on any other part of the fcull, becaufe wounds 
in the cerebellum, which is underneath, are mortal. There are in moil 
fculls, a foramen behind each apophyfis of the occipital bone ; through 
which pafs finufes from the lateral finufes to the external cervical veins: 
By means of thefe communications, as in all other communications of 
