536 A N A T 
ture, the partition dividing thefe cavities is evidently com- 
pofed of two plates, which eafily feparate. Each linns 
commonly opens by a roundiflv fmall hole, at the inner 
and lower-part of the internal angular procelfes, into a 
fimts formed in the nofe., at the upper and back part of 
the os unguis; near to which there are. alio fome other 
fmall finufes of this bone, the greater part of which open 
feparately near tlte feptum narium, and often terminate in 
the fame common canal with the large ones. 
In a natural and found (late, thefe cavities are of confi- 
derable advantage: for, the organ of l’melling being thus 
enlarged, the effluvia of odorous bodies more difficultly 
efcape it; and their iinpreflions, being more numerous, 
are therefore (Ironger, and affedt the organ more. That 
odorous particles may be applied to tire membrane of the 
linufes, is evident from the pain felt in this part of the 
forehead, when the effluvia of volative fpirits, or of ftrong 
aromatics,, are drawn up into the nofe by a quick infpira- 
tion. Thefe, and the other cavities which open into the 
nofe, increale the found of our voice, and render it more 
melodious, by ferving as fo many vaults to refound the 
notes. Hence people labouring under a coryza, or ftoppage 
of tire nofe from any other caufe, when they are by the 
vulgar, though falfely, faid to fpeak through the nofe, 
have inch a difagreeable voice. The liquor feparated in 
the membrane of thefe finufes runs down upon the mem¬ 
brane of the nofe to keep it moift. 
The upper circular part of the os frontis is joined to the 
iifla parietalia, from one temple to the other, by the co¬ 
ronal future. From the termination of the coronal future 
to the external angular procelfes, this bone is connected 
to the fphenoid by the fphenoidal future. At the external 
canthi of the eyes, its angular procefles.are joined by the 
tranfverfe future to the olla mala rum, to which it adheres 
one-third down the outfide of the orbits ; whence to the 
bottom of tliefe cavities, and a little upon their internal 
fides, thefe orbitar procelfes are connedted to the fphenoi¬ 
dal bone by that fame future. 
The frontal bone ferves to defend and fupport the ante¬ 
rior lobes of the brain. It forms a conliderable part of 
the cavities that contain the globes of the eyes, helps to 
make up the feptum narium, organ of fmelling, &c. In 
a rioe child, the frontal bone is divided through the mid¬ 
dle; ‘the luperciliary holes are not formed; often a fmall 
round piece of each orbitar procefs, behind the fuperci- 
liary ridge, is not oflified; and there is no finus to be feen 
within its fubftance. 
Each of the two ojfa parietalia, or bones ferving as walls 
to the encephalon, is an irregular fquare; its upper and 
fore lides being longer than the one behind or below. The 
inferior lide is a concave arch ; the middle part receiving 
the upper round, part of the temporal bone. The exter¬ 
nal furface of each os parietale is convex. Upon it, fonie- 
what below the middle height of the bone, there is a tranf¬ 
verfe arched ridge, generally of a whiter colour than any 
other part of the bone; from which, in bones that have 
ftrong prints of mufcles, we fee a great many converging 
furrows, I ke fo many radii drawn front a circumference 
towards a centre. From this ridge of eaclt bone the tem¬ 
poral mufcle rifes: and, by the prefliire of its fibres, oc- 
cafipns the furrows juft now mentioned. Below thefe we 
obferve, near the femicircular edges, a great many rilings 
and deprefiions, which are joined to like inequalities on 
the infide of the temporal bone, and form the fquamous 
future. The temporal bone may therefore ferve here as a 
buttrefs, to prevent the lower ftde of the parietal from 
ftarting outwards when its upper part is prelfed or ftruck. 
Near the upper lides of thefe bones is a fmall hole in each, 
through which a vein palfes from the teguments of the 
head to the longitudinal linus. In fome Ikulls, one of the 
offii parietalia has not this hole. In others, there are per¬ 
haps two in one bone; and, in fome, not one in either. 
Moll frequently this hole is through both tables ; at other 
times the external hole only is'perforated. The know¬ 
ledge of the courfe of thefe vellels may be of ufe to fur- 
O M Y. 
geons when they make any Ineifion near this part of the 
head ; left, if the vellels are rafhly, cut near the hole, they 
ftn'ink within the fubftance of the bone, and caufe an ob- 
ftinate haemorrhage, which neitheiTigatures nor medicines 
can ftop. 
The olfa parietalia are the mod equal and fmooth, and 
are among the thinned: bones of the cranium ; but they 
enjoy the general ftruftures of two tables and diploe the 
completed. Thefe bones are joined at their fore-fide to 
the os frontis by the coronal future ; at their long inferior 
angles, to the fphenoid bone, by part of the future of this 
name; at their lower edge, to the olfa temporum, by the 
fquamous future, and its pofterior additamentum ; behind, 
to the os occipitis, or olfa triquera, by the lambdoid fu¬ 
ture; and above, to. one another, by the fagittal future. 
The large unoffified ligamentous part of the cranium, 
obfervable between the parietal bones and the middle of 
the divided os frontis of new-born children, called by the 
vulgar the open of the head, was imagined by the ancients 
to ferve for the evacuation of the fuperfluous moifture of 
the brain : and therefore they named it bregma, or the 
fountain; fometimes adding the epithet pu/fatilis, or beat¬ 
ing, cn account of the puliation of the brain felt through 
this flexible ligamento-cartilaginous fubftance. Hence 
the parietal bones are very frequently called ojj'a bregmatis. 
Ojfa temporum, fo named from the hair’s firfl: becoming 
grey on the temples, and thus difeovering people’s ages, 
are each of them equal and fmooth above, with a very 
thin femicircular edge; which, from the mariner of its 
connexion with the neighbouring bones, is diftinguiflied 
by the name ot osfquamofum. Behind this, the upper part 
oi the temporal bone is thicker, and more unequal; and 
is fometimes deferibed as a diftinct part, under the name 
of pars mamillaris. Towards the bale of the fkull, the 
temporal bone appears very irregular and unequal; and 
this part, inftead of being broad, and placed perpendicu¬ 
larly, as the others are, is contradled into an oblong very 
hard fubftance, extended horizontally forwards and in¬ 
wards, which in its progrefs becomes fmaller, and is com¬ 
monly called os petrofum. 
Three external procelfes of each temporal bone are ge¬ 
nerally deferibed. The firft, placed at the lowerand hind 
part of the bone, from its refemblance to a nipple, is call¬ 
ed majloides or mamillaris. It is not folid ; but is compofed 
of cancelli, or fmall cells, which have a communication 
with the large cavity of the ear, the drum ; and therefore 
founds, being multiplied in this vaulted labyrinth, are in- 
creafed before they are applied to the immediate organ of 
hearing. Into the maftoid procefs the fterno-maftoideus 
mufcle is inlerted : and to its back part, where the furface 
is rough, the trachelo-maftoideus and part of the fplenius 
are fixed. About an inch farther forward, the fecond pro¬ 
cefs begins to rife out of the bone; and, having its origin 
continued obliquely downwards and forwards for fome 
way, it becomes fmaller, and is ftretched forwards to join 
with the os mahe; they together forming the bony jugurn, 
under winch the temporal mufcle palfes. Hence this pro¬ 
cefs has been named zygomatic. Its upper edge lias the 
ftrong aponeurolis of the temporal mufcle fixed into it; 
and its lower part gives rife to a (hare of the malfeter. 
From under the craggy part of the os temporum, the 
third procefs (lands out obliquely forwards. The ffiape 
of. it is generally faid to refemble the ancient Jlylus ferip- 
to'rius ; and therefore it is called the Jlyloidprocefs. Some au¬ 
thors however contend, that it ought to be named feloid, 
from its being more like a pillar. Several mufcles have 
their origin from this procefs, and borrow one half of 
their name from it; as fylo-glojfus, fylo-kyoides, fylo-pha - 
ryngeus. This procefs is often, even in adults, not entire¬ 
ly oflified, but is ligamentous at its root, and is fometimes 
compofed of two or three diftinfl pieces. Round the root 
of it, efpecially at the fore-part, there isarifingof the os pe- 
trofum, which fome authors have efteemed a procefs: 
and, from the appearance it makes with the ftyliform, have 
named it vaginalis. Others again have, under the name of 
3 auditory 
