55* 
ANA' 
of this rib is not divided into two plain furfaces by a mid¬ 
dle ridge, b'ecaufe it is only articulated with the firft Ver¬ 
tebra of the thorax. Jts cartilage is oflificd- in adults, 
and is united to the fie mum at right angles. This firft rib 
frequently has a ridge rifmg near the middle of its pofte- 
rior edge, where one of the heads of the fcalenus mufcles 
rifes. Farther forward it is Hatted, or fometimes depreff- 
ed by the clavicle. The fifth, lixth, and feventh, or ra¬ 
ther the lixth, feventh, eighth, and fometimes the fifth, 
fixth, feventh, eighth, and ninth, ribs, have their carti¬ 
lages at lead contiguous : and they are frequently joined 
to each other by crofs cartilages ; and mod commonly the 
cartilages of the eighth, ninth, and tenth, are connected to 
the former and to each other by firm ligaments. The 
eleventh, and fometimes the tenth, rib, has no tubercle 
for its articulation with the tranlverfe procefs of the ver¬ 
tebra, to which it is only loofely fixed by ligaments. The 
folfa in its lower edge is not fo deep as in the upper ribs, 
becaufe the veffels run more towards the interface between 
the ribs. Its fore-end is fmaller than its body, and its 
ihort fmall cartilage is but loofely connected to the carti¬ 
lage of the rib above. The twelfth rib is the Ihorteftand 
ftraightelf. Itsliead is only articulated with the lalt ver¬ 
tebra of the thorax ; therefore it is not divided into two 
furfaces. To its whole internal fide the diaphragm is con¬ 
nected. 
The Jlernum, or breaf-bone , is the broad flat bone, or pile 
of bones, at the fore-part of the thorax. The number of 
bones into which this fliould be divided, has occafioncd 
debates among anatomills, who have conlidered itinfub- 
jeCts of different ages. In adults of a middle age, it is 
conipofed of three bones, which ealily feparate after the 
cartilages connecting them are dellroyed The two lower 
bones are frequently found intimately united; and very 
often, in old people, the (termini is a continued bony fub- 
ltance from one end to the other; though we (till obferve 
two, fometimes three, tranlverfe lines on its furface; which 
are marks of the former divifions. When weconfider the 
fternum as one bone, we find it bfoadeft and thickelt above, 
and becoming fmaller as it defcends. The internal fur- 
face is fomewhat hollowed for enlarging the thorax : but 
the convexity on the external furface is not fo confpicu- 
ous, becaufe the (ides are prefled outwards by the true 
ribs; the round heads of whofe cartilages are received in¬ 
to (even fmooth pits formed in each lide of the fternum, 
and are kept firm there by flrong ligaments, v, Inch on the 
external furface have a particular radiated texture. The 
cartilaginous fibres frequently thruft themfelves into the 
bony fubftance of the fternum, and are joined by a fort of 
future. The pits at the upper-part of the fternum are at 
the greateft diftance one from another, and, as they de- 
fcend, are nearer; fo that the two loweft are contigu¬ 
ous. 
The fubfance of the breaft-bcne is cellular, with a very 
thin external plate, efpecially on its internal furface, where 
we may frequently obferve a cartilaginous cruft fpread over 
it. On both furfaces, however, a ftrong ligamentous 
membrane is clofely braced; and the cells of this bone are 
fo frnall, that a confiderable quantity of offeous fibres muff 
be employed in the competition of it. Whence, with the 
defence which the mufcles give it, and the moveable fup- 
port it has from the cartilages, it is fufficiently fecured 
from being broken ; for it is ftrong by its quantity of bone, 
its parts are kept together by ligaments, and it yields 
enough to elude confiderably any violence offered. 
The fternum is joined by cartilages to the feven upper 
ribs, unlefs w hen the firft coalelces with it in an intimate 
union of fubftance; and its unequal cavity on each fide of 
its upper end is fitted for the ends of the clavicles. The 
vfes of tiiis bone are, to afford origin and infertion to fe- 
veral mufcles; to fuftain the mediaftinum : to defend the 
vital organs, the heart and lungs, at the fore-part; and, 
daftly,, by ferving as a moveable- fulcrum of the ribs, to 
aflift confiderably in refpiration. 
" O M Y. 
OF THE SUPERIOR EXTREMITIES. 
Authors are much divided in their opinions about the 
number of bones of which each fuperior extremity fliould 
he faid to confift ; fome defcribing the clavicle and fcapula 
as part ot it, others chiding thefe two bones with thole of 
the thorax ; but fince moft quadrupeds have no clavicles, 
and the'human - thorax can perform its functions right 
when the fcapula is taken away, while it is impoffible for 
us to have the right ufe of our arms without thefe bones, 
it feems evident that they belong to the fuperior extremi¬ 
ties'. Each of the fuperior extremities may be divided 
into the Ihoulder, arm, fore-arm, and hand. 
The fhouldir confiftsof the clavicle and the fcapula. The 
clavicuta , or collar-bone , is the long crooked bone placed 
aimoft horizontally betw een the upper lateral part of the 
fternum and what is commonly called the top of the 
(boulder; which, as a clavis or beam, bears off from.the 
trunk ol the body. The clavicle is larger at its two ends 
than in the.middle. The end next to the fternum is trian¬ 
gular: the angle behind is confiderably protruded, to form 
a (harp ridge, to which the tranfverfe ligament, extended 
from one clavicle to the other, is fixed. The middle of 
this protuberant end is as irregularly hollowed as the ca¬ 
vity in the fternum for receiving it is raifed; but, in a re¬ 
cent fubjeCt, the irregular concavities of both are fupplied 
by a moveable cartilage; which is not only much more 
clofely connected by ligaments to'the circumference of the 
articulation than thofe of the lower jaw are, but it grows 
to the two bones at their internal and external ends; its 
fubftance at the external end being foft, but very ftrong, 
and refembling the intervertebral cartilages. From this in¬ 
ternal end, the clavicle, for about two-fifths of its length, 
is bended obliquely forwards and downwards. On the up T 
per and fore-part of this curvature a fmall ridge is feen, 
with a plain rough furface before it; whence the mufculus 
fterno-hyoideus and (ferno-maitoideus have in part their 
origin. Near the lower an^le a fmall plain furface is often 
to be remarked, where the firft rib and this bone are con¬ 
tiguous, and are connected by a firm ligament. From this 
a rough plain furface is extended outwards, where the 
peCtcral muff le lias part of its origin. Behind, the bone 
is made flat and rough by the infertion of the larger (hare 
of the fubclavian mufcle. After the clavicle begins to be 
bent backwards, it is round : but it foon after becomes 
broad and thin, which lhape it retains to its external end. 
Along the external concavity, a rough finuofity runs, from 
which fome part of the deltoid mufcle takes its rite; op- 
pofite to this, on the convex edge, a fcabrous ridge gives 
infertion to a (hare of the cncullaris mufcle. The upper 
furface of the clavicle is here flat; but the lower is hollow, 
for lodging the beginning of the mufculus fubclavius ; 
and towards its back part a tubercle riles; to which, and 
to a roughnefs near it, the ftrong ftiort thick ligament, 
connecting this bone to the coracoid procefs of the fcapula, 
is fixed. The external end of this bone is horizontally 
oblong, fmooth, (loping at the pofterior (ide, and tipped, 
in a recent fubjeCt, witli a cartilage, for its articulation 
with the acromion fcapula. Round this the bone is fpongy, 
for the firmer connection of the ligaments. The medullary 
ar teries, having th^ir direction obliquely outwards, enter 
the clavicles by one or more fmall paffages in the middle 
of their back-part. The nfes of the clavicles are, to keep 
the fcapula, and confequently all the fuperior extremities, 
from falling in and forward upon the thorax; by which, 
as in moft quadrupeds, the motions of the arms would be 
much confined, and the bread made too narrow. The 
clavicles likewife afford origin to feveral mufcles, and a 
defence to large velfels. From the lunation, figure, and 
life, of the clavicles, it is evident that they are much ex- 
pofed to fraftures; that their broken parts mult generally 
pa-fs each other; and that they are with difficulty kept in 
their place afterwards. 
The fcapula , or [houlder-blade, is the triangular bone fitu- 
ated on the outlide of the ribs; with its longeft fide, called 
its 
