ANATOMY. 
gland has been often found to contain gravel. Below the 
glandula pinealis there is a medullary tranfverfe cord, call¬ 
ed the pojlerior commiffure of the hcmifpher cs of the cerebrum. 
The cerebellum is contained under the tranfverfe feptum 
of the dura mater, in the underand back part of the cra¬ 
nium. It confifts, like the cerebrum, of two fubftar.ees. 
It has no circumvolutions on its furfa.ee; but, inftead of 
them, numerous fnlei, which are deep, and difpofed in 
fuch a manner as to form thin flat ftrata, more or lefs hori¬ 
zontal, between which the internal lamina of the pia mater 
infinuates itlelf by a number of fepta equal to that of the 
ftrata. Under the tranfverfe feptum, it is covered by a 
vafcular texture, which communicates with the plexus 
choroides. It has two middle eminences, called appendices 
vermiformes, from their refemblance to the rings of an 
earth-worm. Befides the divilion of the cerebellum into 
lateral portions, or into two lobes, each of thefe lobes 
feems to be like wife fub-divided into three protuberances; 
one anterior, one middle or lateral, and one pofterior. 
When we feparate the two lateral lobes, we difeover the 
pofterior portion of the medulla oblongata; and, in the 
pofterior furface of this portion, from the tubercula qua- 
drigemina, we obferve an oblong cavity, which is called 
the fourth ventricle-, this terminates backward, like the 
point of a writing pen. Hence the undercnd of it is call¬ 
ed calamus feriptorius. At the beginning of this cavity we 
meet with a thin medullary lamina, which conftitutes a 
valve between that canal and the fourth ventricle. It is 
lined by a thin membrane, and feems often to be diftin- 
guilhed into two lateral parts, by a kind of fmall groove, 
from the valvular lamina to the point of the calamus ferip¬ 
torius. This membrane is a continuation of that part of 
the pia mater which lines the fmall canal, the third ven¬ 
tricle, infundibulum, and the two great ventricles. To 
be able to fee the fourth ventricle in its natural ftate, in 
which it is narrovveft, it muft be laid open while the cere¬ 
bellum remains in the cranium. On each fide of this ven¬ 
tricle, the medullary fubftance forms a trunk which ex¬ 
pands itfelf in form of laminae through the cortical ftrata. 
But here we find the medullary bearing a lefs proportion 
to the cortical than it does in the cerebrum. We difeo¬ 
ver thefe medullary laminae according to their breadth, 
by cutting the cerebellum in fiices almoft parallel to the 
bafis of the cerebrum ; but, if we cut one lobe of the ce¬ 
rebellum vertically, the medullary fubftance will appear 
to be difperfed in ramifications through the cortical fub¬ 
ftance. Thefe ramifications have been named arbor vita-, 
and the two trunks, from whence thefe different laminae 
arife, are called pedunculi cerebelli. 
The medulla oblongata is a medullary fubftance, fituated 
in the middle part of the bafes of the cerebrum and cere¬ 
bellum, without any difeontinuation, between the lateral 
parts of both thefe bafes ; and is juftly efteemed to be a 
third general part of the whole mafs of the brain, or as 
the common production, or united elongation, of the whole 
medullary fubftance of the cerebrum and cerebellum. 
The lower fide of the medulla oblongata, in an inverted fi- 
tuation, prefents to our view feveral parts, which are in 
general either medullary productions, trunks of nerves, or 
trunks of blood-veftels. The chief medullary productions 
are thefe; the large or anterior branches of the medulla 
oblongata, which have likewife been named crura anterio- 
ra, femora, and brachia medulla: oblongatce, and pedunculi ce. 
rebri. The tranfverfe protuberance, called likewife pro- 
ceffus annularis or pons Varolii. The fmall or pofterior 
branches, called pedunculi cerebelli, or crura pofieriora medulla 
oblongata. The extremity or cauda of the medulla ob¬ 
longata, with two pairs of tubercles; one of which is na¬ 
med corpora olivaria, the other corpora pyramidalia ; and to 
all thefe productions we muft add a production of the in¬ 
fundibulum and two medullary papillae. The great branch¬ 
es of the medulla oblongata are two very considerable me¬ 
dullary fafciculi. Thefe fafciculi are flat, much broader 
before than behind; their furfaces being compofed of fe¬ 
veral longitudinal anddiftinCUy prominent medullary fibres. 
Voi. I. No. 38. 
59 3 
Their anterior extremities feem to be loft at the lower part 
of the corpora ftriata ; and, it is for that reafon that they 
are efteemed the pedunculi of the cerebrum. The tranf¬ 
verfe annular protuberance is a medullary production, 
which feems at firft fight to furround the pofterior extre¬ 
mities ol the great branches; but the medullary fubftance 
of the protuberance is in reality intimately mixed with 
that of the two former. Variolus, an ancient Italian au¬ 
thor, viewing thefe parts in an inverted fituation, compa¬ 
red the two branches to two rivers, and the protuberance 
to a bridge over them both ; and from thence it has the 
name of pons Varolii. When we cut into the fubftance of 
the pons, we find much cortical fubftance within it, and 
this formed into ftriae, which run in various directions. 
The fmall branches of the medulla oblongata are lateral 
productions of the tranfverfe protuberance, which by their 
roots feem to encompafs that medullary portion in which 
the fourth ventricle or calamus feriptorius is formed. They 
form in the lobes of the cerebellum, on each fide, thole 
medullary expanfions, a vertical feCtion of which (hews the 
white ramifications commonly called arbor vita ; and they 
may be juftly ftyled pedunculi cerebelli. The extremity is 
no more than the medulla oblongata contracted in its paf- 
fage backward to the anterior edge of the foramen magnum, 
of the os occipitis, where it terminates in the medulla fpi- 
nalis; and, in this part of it, feveral things are to be taken 
notice of. We fee, firft of all, four eminences, two named 
corpora olivaria, and the other two corpora pyramidalia. Im¬ 
mediately afterwards, it is divided into two lateral portions 
by two narrow grooves, one on the upper fide, the other 
on the lower. They both run into the fubftance of the 
medulla, as between two cylinders, flatted on that fide by 
which they are joined together. When we feparate thefe 
ridges with the fingers, we obferve a crucial intertexture 
of feveral fmall medullary cords, which go obliquely from 
the fubftance of one lateral portion into the fubftance of 
the other. M. Petit, member of the Royal Academy of 
Sciences, and doCtor of phyfic, is the author of this dif- 
covery, by which we are enabled to explain feveral phe¬ 
nomena, both in phyfiology and pathology. The corpora 
olivaria and pyramidalia are whitilh eminences, fituated 
longitudinally near each other, on the lower fide of the 
extremity or cauda, immediately behind the tranfverfe or 
annular protuberances. The corpora pyramidalia are in 
the middle ; fo that the interftice between them, which is 
only a kind of fuperficial groove, anfwers to the inferior 
groove of the following portion. The corpora olivaria are 
two lateral eminences fituated at the outfide of the former, 
and are thus termed by Willis, Duverney, Haller, &c. but 
Window reverfes the names. Thefe four eminences are 
fituated on the lower half of the medulla; which obferva- 
tion we here repeat, to make it be remembered, that, in 
all the figures and demonftrations, thefe parts are repre- 
fented as fuperior, which, in their natural fituation, are 
inferior. Thus thefe eminences are under the fourth ven¬ 
tricle, and under the pedunculi cerebelli. The tubercula 
mammillaria, which are fituated very near the production 
of the infundibulum, have been taken for glands; proba¬ 
bly becaufe of their greyilh inner fubftance, which, how¬ 
ever, does not feem to be different from that of feveral 
other eminences of the medulla oblongata. And, for that 
reafon, we'choofe rather to call them, from their figure, 
tubercula mammillaria , than papilla medullares. Thefe tu¬ 
bercles feem to have fome immediate relation to the roots 
or bafes of the anterior pillar of the fornix ; fo that we 
might call them, as M. Santorini has done, the bulbs of 
thefe roots, though they appear to be likewife a part of a 
continuation of other portions of the cortical and medul¬ 
lary fubftance, of a particular texture. The beak or tube 
of the infundibulum is a very thin production from the 
fides of that cavity ; and it is Itrengthened by a particular 
coat given to it by the pia mater. It is bent a little from 
behind forward, toward the glandula pituitaria, and after¬ 
wards expands again round this gland. The membrana 
arachnoides, or external lamina of the pia mater, appears 
7 M 10 
