A N A r 
flown by a tendinous fheath extended acrofs the folia; in 
which, and in the neighbouring tubercles, are feveral re¬ 
markable holes, which are penetrated by the tendinous 
and ligamentous fibres, and by velfels. On each fide of 
this folia, as it defcends in the os humeri, a rough ridge, 
gently flatted in the middle, runs from the roots of the 
tubercles.' The tendon of the pettoral mufcle is fixed into 
the anterior of thefe ridges, and the latiffimus dorfi and 
teres major are inferted into the Internal one. A little 
behind the lower end of this laft, another rough ridge 
may be obferved, where the coraco-brachialis is inferted. 
From the back-part of the root of the largeft tubercle a 
ridge alfo is continued, from which the brevis extenfor 
cubiti riles. This bone is flatted on the infide, about its 
middle, by the belly of the biceps flexor cubiti. In the 
middle of this plain furface, the entry of the medullary 
artery is feen flanting obliquely downwards. At the fore- 
lide of this plane the bone rifes in a fort of a ridge, which 
is rough, and often has a great many fmall holes in it, 
where the tendon of the ftrong deltoid mufcle is inferted; 
on each fide of which the bone is fmooth and flat, where 
the brachius interims rifes. The exterior of thefe two flat 
furfaces is the largeft ; behind it a fuperficial fpiral chan¬ 
nel, formed by the mufcular nerve and the velfels that 
accompany it, runs from behind forwards and downwards. 
The body of the os humeri is flatted behind by the ex- 
tenfors of the fore-arm. Near the lower end of this bone, 
a large fharp ridge is extended on its outfide, from which 
the mufculus fpinator radii longus, and the longeft head 
of the extenfor carpi radialis, rife. Oppofite to this, there 
is another fmall ridge to which the aponeurotic tendon, 
that gives origin to the fibres of the internal and external 
brachial mufcles, is fixed ; and from a little deprellion on 
the fore-fide of it, the pronator radii teres rifes. 
The body of the os humeri becomes gradually broader 
towards the lower end, where it has feveral proceffes ; at 
the roots of which there is a cavity before and another 
behind. The anterior is divided by a ridge into two; the 
external, which is the leaft, receives the end of the radius ; 
and the internal receives the coronoid procefs of the ulna 
in the flexions of the fore-arm, while the pofterior deep tri¬ 
angular cavity lodges the olecranon in the extenfions of 
that limb. The bone between thefe two cavities is prefled 
fo thin by the procelles of the ulna, as to appear diapha¬ 
nous in feveral fubjefts. The fides of the pofterior cavity 
are ftretched out into two proceffes, one on each fide : 
thefe are called condyles ; from each of which a ftrong li¬ 
gament goes out to the bones of the fore-arm. The ex¬ 
ternal condyle, which lias an oblique direction alfo for¬ 
wards in refpeft of the internal, when the arm is in the 
moftnatural pofture, is equally broad, and has an oblufe 
fmooth head lifing from it forwards. From the rough 
part of the condyle, the inferior heads of the bicornis, the 
extenfor digitorum communis, extenfor carpi ulnaris, an- 
conaeus, and fome part of the fpinator radii brevis, take 
their rife; and on the fmooth head the upper end of the 
radius plays. Immediately on the outfide of this, a finu- 
olity is made by the fhorter head of the bicornis mufcle, 
upon which the mufcular nerve is placed. The internal 
condyle is more pointed and protuberant than the exter¬ 
nal, to give origin to fome part of the flexor carpi radia¬ 
lis, pronator radii teres, palmaris longus, flexor digitorum 
fublimis, and flexor carpi ulnaris. Between the two con¬ 
dyles, is the trochlea or pulley ; which confifts of two late¬ 
ral protuberances, and a middle cavity, that are fmooth 
and covered with cartilage. When the fore-arm is ex¬ 
tended, the tendon of the internal brachiieus mufcle is 
lodged in the fore-part of the cavity of this pulley. The 
external protuberance, which is lefs than the other, has 
a lharp edge behind ; but forwards, this ridge is obtufe, 
and only feparated from the little head, already defcribed, 
by a fmall folia, in which the joined edges of the ulna and 
radius move. The internal protuberance of the pulley is 
largeft and hig'neft ; and therefore, in the motions of the 
ulna upon it, that bone would be inclined outwards, were 
Vol. I. No. 35. 
r O M Y. 5?3 
it not fupported by the radius on that fide. Between this 
internal protuberance and condyle, a fmuofity may be re¬ 
marked, where the ulnar nerve palfes. The round head 
of the os humeri is articulated with the glenoid cavity of 
the fcapula ; which being fuperficial, and having long li¬ 
gaments, allows the arm a free and extenfive motion. The 
lower end of the os humeri is articulated with the bone of 
the fore-arm, and carries them with it in all its motions, 
but ferves as a bale on which they perform the. motions 
peculiar to themlelves. 
The fore-arm conlifts of two long bones, the ulna and 
radius. The ulna, lo named from its being ufed as a mea- 
ftire, is the longeft of the two, and lituated on the outfide 
of the radius. At the upper end of the ulna are two pro- 
ceft'es : the pofterior is the largeft, and formed like a hook, 
whole concave furface moves upon the pulley of the os 
humeri, and is called olecranon, or top of the cubit. The 
convex back-part of it is rough and fcabrous, where the 
longus, brevis, and brachiaeus extermrs, are inferted. The 
anterior procefs is not fo large, nor does it reach fo high, 
as the one behind; but is iharper at its end, and there¬ 
fore is named coronoid. Between thefe two procelles, a large 
femicircular or ligmoid concavity is left; the furface of 
which, on each tide of a middle riling, is flanting, and 
exactly adapted to the pulley of the bone of the arm. Im¬ 
mediately below the olecranon, on the back-part of the 
ulna, a flat triangular fpongy lurface appears, on which 
we commonly lean. At the internal fide of this, there is 
a larger hollow furface, where the mufculus ancomeus is 
lodged ; and the ridge at the inlide of this gives rife to the 
mufculus fupinator radii brevis. Between the top of the 
ridge and the coronoid procefs is the femilunated fmooth 
cavity, lined with cartilage ; in which, and in a ligament 
extended from the one to the other end of this cavity, the 
round head of the radius plays. Immediately below it, a 
rough hollow gives lodging to mucilaginous glands. Be¬ 
low the root of the coronoid procefs, this bone is fcabrous 
and unequal, where the brachiaeus internus is inferted. 
The body of the ulna is triangular. The internal angle 
is very fliarp where the ligament that connects the two 
bones is fixed : the fides which make this angle are flat and 
rough, by the aftion and adhelion of the many mufcles 
which are lituated here. At the diltance of one-third of 
the length of the ulna, the paflage of the medullary velfels 
may be feen flanting upwards. The external fide of this 
bone is fmooth, fomewhat convex, and the angles at each 
edge of it are blunted by the preflure of the mufcles e- 
qually dil'pofed about them. As this bone defcends, it 
becomes gradually fmaller; fo that its lower end termi¬ 
nates in a little head, Handing on a fmall neck. Towards 
the fore but outer part of which laft, an oblique ridge 
runs, that gives rife to the pronator radii quadrants. The 
head is round, fmooth, and covered with a cartilage on 
its internal fide, to be received into the femilunar cavity 
of the radius ; while a ftyloid procefs rifes from its outfide, 
to which is fixed a ftrong ligament that is extended to the 
os cuneiforme and pififorme of the wrift. Between the 
back-part of that internal fmooth fide and this procefs, a 
finnofity is left for the tendon of the extenfor carpi ulna¬ 
ris. On the fore-part of the root of the procefs, Inch 
another deprellion may be marked for the paflage of the 
ulnar artery and nerve. 
The radius, fo called from its imagined refemblance to 
a fpoke of a wheel, or to a weaver’s beam, is the bone 
placed on the inlide of the fore-arm. Its upper end is 
formed into a circular little head, which is hollowed for 
an articulation with the tubercle at the fide of the pulley 
of the os humeri. Below the head, the radius is much 
fmaller ; therefore this part, which is made round by the 
aflion of the fupinator radii brevis, is named its cervix. 
At the external root of this neck, a tuberous procefs rifes; 
into the outer part of which the biceps flexor cubiti is in¬ 
ferted. From this a ridge runs downwards and inwards, 
where the fupinator radii brevis is inferted ; and a little 
below, and behind this ridge, there is a rough fcabrous 
7 B furface. 
