ANATOM Y. 
very cold; more efpecially when the air is damp, the body 
unexercifed, rhe mind op p re tied with grief, or botli under 
conditions contrary to thofe which increafe perfpiration be¬ 
fore-mentioned. Tliefe veins, fays Haller, are demonftra- 
ted by anatomical injections, which, if thin or watery, 
fweat through them as through the arteries: but, accord¬ 
ing to later phyfiologifts, ablorption is' performed folely 
by the lymphatic velfels. That ablorption takes place, is 
fufficiently proved by the manifeft operation of medicines, 
pervading tlie air, or applied to the Ikin; fuch as the va¬ 
pours of mercury, turpentine, faffron, waters of baths, 
mercurial plalters, tobacco, coloquintida, opium, cantha- 
rides, arfenic, with the fatal effects of contagious or other 
poifons entering through the Ikin ; as in the venereal in¬ 
fection. Another proof of abforption by the Ikin is, that 
animals live in hot moift climates without drink, and yet 
difcharge a confiderable quantity of humours both by per¬ 
fpiration and urine. Laftly, abforption has been proved 
in fome dileafes where a much greater quantity of urine 
has been difcharged than the quantity of drink taken in. 
It is difficult to ascertain the quantity of this inhaled mat¬ 
ter in animals; in plants it appears, from well-authentica¬ 
ted experiments, to be very confiderable, efpecially during 
the night. Thefe cutaneous velfels, both exhaling and 
inhaling, are capable of contraction and relaxation by the 
power of the nerves. The truth of this appears from the 
effects of the paffions of the mind; which, if joyful, in- 
-creafe the circulation, and relax the exhaling velfels, fo as 
to yield ealier to the impulfe of the blood ; from whence, 
with a ffibrtening of the nerves, there follows a rednefs, 
moifture, and turgefcerice, of the Ikin. Thofe pallions, 
on the contrary, which are forrowful, and retard the cir¬ 
culation, contraCt the exhaling velfels; as appears from 
the drynefs and corrugation of the Ikin, like a goofefiiu, 
after frights; and from a diarrhoea being caufed by fear. 
And the fame affections feem to open and increafe the 
power of the inhaling velfels, whence the variolous or 
peltilential contagions are ealily contracted by fear. 
Of the DIFFERENT VISCERA and ORGANS. 
Of the HEAD. 
TI 1 E head is generally confidercd as one of the three 
principal cavities of the human body. On its outfide are 
fituated tire leats and bales of feveral very complex parti¬ 
cular organs; whereas on the inlide it contains only one, 
namely the brain, which is indeed the primum mobile of 
the whole animal cecononty. The mechanifm of this or¬ 
gan is very little known; and the ItruCture of its different 
parts, even of thofe with which we are fuppofed to be molt 
acquainted, is very difficult to be demonftrated. 
The brain is that mafs which fills the cavity of the cra¬ 
nium, and which is immediately furrounded by two mem¬ 
branes, called meninges by the Greeks, and matres by other 
ancients, becaufe they were commonly of opinion, that 
thefe membranes were the origin, and, as it w ere, the mo¬ 
ther, of all the other membranes of the body. This ge¬ 
neral mafs is divided into three particular portions ; the 
cerebrum or brain properly fo called, the cerebellum, and 
medulla oblongata. To thefe three parts contained within 
the cranium, a fourth is added, which fills the great canal 
of the fpina dorfi, and is known by the name of medulla 
fpinalis, being a continuation of the medulla oblongata. 
The meninges, or membranes, are two in number ; one of 
which is very ftrong, and lies contiguous to the cranium; 
the other is very thin, and immediately touches the brain. 
The firft is named dura mater , the fecond pia mater. This 
fall is again divided into two; the external lamina being 
termed arachncidcs, the internal retaining the common name 
of pia mater. 
The dura mater inclofes the brain and all its appendages. 
It lines the inlide of the cranium, and fupplies the place 
of an internal periofteum, being fpread in holes and de- 
preffions, and covering all the eminences in fuch a man¬ 
ner, as to prevent their being hurtful to the brain. It 
fends off feveral proceffes j three of which form particular 
fepta, that divide the brain into certain parts. One of 
them is luperior, reprefenting a kind of medialtinum be¬ 
tween the two great lobes of the brain. The fecond is in 
a middle fituaiion like a diaphragm, between the cerebrum 
and cerebellum. The third is inferior between the lobes 
of the cerebellum. The luperior feptum Is longitudinal, 
in form of a Icythe, whence it is termed the falx f the 
dura mater ; and it may likewife be called feptum Jagittalc, 
xierticale, or mediafinum cerebii. The middle feptum is 
tranfverfe, and might be called the floor of the cerebrum, 
the diaphragm of the brain , tentorium cercbelli. The inferior 
feptum is very fmall, and runs down between the lobes of 
the cerebellum; on which account it may be termed either 
limply feptum ccrebe/li, or feptum occipilale minus, the middle 
partition being looked upon as the feptum oceipitale mu- 
jus. The dura mater contains in its duplicature feveral 
particular canals, into which the venous blood, not only 
of that membrane, but of the whole brain, is carried. 
Thefe canals are termed fmufes ; and fome of them are 
difpofed in pairs, others in uneven numbers; that is, iome 
of them are placed alone in a middle lituation ; others are 
difpofed laterally on each fide of the brain. All thefe 
finufes communicate with each other, and with the great 
lateral finufes, by which they difcharge themfelves into 
tire internal jugular veins, which are only continuations of 
thefe lateral finufes. They likewife unload themfelves, 
partly into the vertebral veins, which communicate with 
the fmall lateral or inferior occipital finufes; and partly 
into the external jugular veins, by the orbitary finufes, 
which communicate with the venae angulares, frontales, 
nafales, maxillares, See. as the lateral finufes likew ife com¬ 
municate with the vena; occipitales, &c. Thus the blood, 
which is carried to the dura mater, &c. by the external 
and internal carotid, and by the vertebral arteries, is re¬ 
turned to the heart by the external and internal jugular 
and vertebral veins; fo that the blood, if obliriuffed in one 
place, finds, in confcquence of thefe communications, a 
paffage at another, though perhaps not w ith the lameeafe. 
This obfervation is of confequence, in relation not only to 
obflrmffions, but to the different lituationsof the head. 
It lias been thought, that the arteries of the dura mater 
difcharged themfelves immediately into the finufes; be¬ 
caufe injections made by the arteries, or a hog’s bridle 
thrult into them, have been found to pafs into thefe finu¬ 
fes. But, on a more clofe examination, it has been difeo- 
vered, that the injection? palled from the arteries into the 
veins, and from thence into the finufes ; and that the hog.’s 
bridle pierced the (ides of the artery, which are very thin 
near the finufes. This midake gave rile to another, name¬ 
ly, that the dura mater had no veins; and what confirmed 
it was, that the arteries of the dura.mater cover the veins 
fo entirely, that the edges of the veins aire hardly per¬ 
ceivable on cither fide of the arteries. There are, how¬ 
ever, fome places where the veins, being broader than the 
arteries, their two edges are feen on each fide of the arte¬ 
ries like capillary velfels, Thefe veins are, for the mod 
part, branches of thefe finufes, and the fmall trunks of 
fome of them open into the head of the vena jugnlaris in¬ 
terna. The prominent fibres which appear interfering 
eacli oilier in different manners on the inlide of the dura 
mater, efpecially near the falx and tranfverfe feptum, and 
which have been taken for a kind of flefity fibres, feem to 
be only ligamentary and eladic. The univerfal adhelion 
of this membrane to the cranium, proves that it can have 
no particular motion, and confequently, that fuch flelhy 
or mufcular fibres would be altogether ufelcfs. This ad- 
hefion w'as plainly demondrated by Vcfalius, Riolan, &c„ 
long before Roonhuyfen. 
The pia mater is a much fofter and finer membrane than 
the former, being exceedingly delicate, tranfparent, and 
vafcular; and is connected to the dura mater only by the 
veins which open into the finufes. It is compofed of two 
laminae, of which the external one is named tunica arach- 
noidca, from its refemblance to a cobweb. They adhere 
clofely to each other at the upper part of the brain; but 
z are 
