ANATOMY. 
fes. The fpinal proceffes are long, fmall-pointed, and do¬ 
ing downwards and backwards: from their upper and 
ack part a ridge riles, which is received by a frnall chan¬ 
nel in the fore-part of the fpinal procefs immediately above, 
which is here connected to it by a ligament. The conduit 
of the fpinal marrow is here more circular, but, corre- 
fp.onding to the fize of that cord, is fmaller than in any 
of the other vertebra:; and a larger fltare of the holes in 
the bony bridges, for the t'ranfmifiion of the nerves, is 
formed in the vertebra above than in one below. The 
connection of the dorfal vertebrae to the ribs, the thin- 
nefs of their cartilages, the eredt fituation of the oblique 
proceffes, the length, (loping, and connection, of the fpinal 
pro cedes, all contribute to re (train thefe vertebras from 
much motion, which might dilturb the aCtions of the heart 
and lungs; and, in confequence of the little motion allow¬ 
ed here, the intervertebral cartilages fooner thrivel, by be¬ 
coming more folid ; and therefore the firft remarkable cur¬ 
vature of the fpine obferved, as people advance to old 
age, is in the lead (tretched vertebrae of the back; or old 
people firft become round (liouldered. 
The lowed order of the true vertebrae is the lumbar , 
which are five bones, that may be diftinguiflied from any 
other by thefe marks: i. Their bodies, though of a cir¬ 
cular form at their fore-part, are fomewhat oblong from 
one fide to the other; which may be occalioned by the 
prelTure of the large veffels, the aorta and cava, and of the 
vifeera. The epiphyfes on their edges are larger; and 
therefore the upper and lower furfaces of their bodies are 
more concave than in the vertebrae of the back. 2. The 
cartilages between thefe vertebrae are much the thickeft of 
any, and render the fpine convex within the abdomen, by 
their greateft thicknefs being at their fore-part. 3. The 
oblique precedes are ftrong and deep; thofe in oppofite 
iides being almoft placed in parallel planes; the fuperior, 
which are concave, facing inwards, and the convex infe¬ 
rior ones facing outwards. And therefore each of thefe 
vertebrae receives the one above it, and is received by the 
one below ; which is liot fo evident in the other two claffes 
already described. 4. Their tranfverfe proceffes are fmall, 
long, and almoft ereft, for allowing large motion to each 
bone, and diffident infertion to mufcles, and forfupport- 
ing and defending the internal parts. 5. Between the roots 
of the luperior oblique and tranfverfe proceffes a fmall pro¬ 
tuberance may be obferved, where fome of the mufcles 
that raife the trunk of the body are inferted. 6. Their 
fpinal proceffes are ftrong, ftraight, and horizontal, with 
broad flat Tides, and a narrow edge above and below; this 
laft being depreffed on each fide by mufcles. And at the 
■root of thefe edges, we fee rough furfaces for fixing the 
ligaments. 7. The canal for the numerous cords called 
cauda equina, into which the fpinal marrow divides, is ra¬ 
ther larger in thefe bones than what contains that marrow 
in the vertebrae of the back. 8. The holes for the pal- 
fage of the nerves are more equally formed out of both 
the contiguous vertebrae than in the other claffes ; the up¬ 
per one furnifties, however, the larger (hare of each hole.' 
The lumbar vertebrae, as they defcend, have their oblique 
proceffes at a greater aiftance from each other, and facing 
more backwards and forward's. Both tranfverfe and fpinal 
proceffes of the middlemoft vertebrae of the loins are long- 
eft: and thickeft; in the vertebrae above and below, they 
■are lefs. So that thefe proceffes of the firft and fifth are 
the lead, to prevent their ftriking on the ribs or offa ilium, 
or their bruifing the mufcles in the motions of the fpine. 
The epiphyfes round the edges of the bodies of the lum¬ 
bar vertebras are mod raifed in the two lowed ;■ which con¬ 
sequently make them appear hollower in the middle than 
the others are. The body of the fifth vertebra is rather 
thinner than that of the fourth. The fpinal procefs of 
this fifth is fmaller, and the oblique proceffes face more 
backwards and forwards than in any other lumbar vertebra. 
■ After confidering the ftrudture 0/ the particular verte¬ 
bra:, and their mutual connection, we may obferve a fo- 
Jicitous care taken that they (hall not be disjoined without 
?47 
great difficulty. For, befides being connected by ftrong 
ligaments proportioned to the forces which are to be refill¬ 
ed, their bodies either enter fo into each other as to pre¬ 
vent their being difplaced any way, as in the vertebrae of 
the neck; or they are propped on all tides, as thofe of the 
back are by the ribs; or their furfaces of contaft are fo 
broad, as to render the feparation almoft impracticable, as' 
in the loins : while the depth and articulation of the oblique 
proceffes are exaCtly proportioned to the quantity of mo¬ 
tion which the other parts of the bones allow, or the muf¬ 
cles can perform. Yet as thefe oblique proceffes are fmall, 
and therefore not capable of fo fecure a conjunction as the 
larger bodies, they may fooner yield to a disjoining force ; 
but then their diflocation is not of fo near bad confequence 
as the feparation of the bodies would be : for, by the oblique 
proceffes being dillocated, the mufcles, ligaments, and (pi- 
nal marrow, are indeed (tretched; but this marrow mult 
be compreffed, or entirely deltroyed, when the body of the 
vertebra is removed out of its place. 
The falfe vertebrae compofe the under pyramid of the 
fpine. They are diftinguiflied from the bones already de- 
fcribed juftly enough by the epithet of falle; becaufe, 
though each bone into which they can be divided in young 
people refembles the true vertebrae in figure, yet none of 
them contribute to the motion of the trunk of the body; 
they being intimately united to each other in adults, ex¬ 
cept at their lower part, where they are moveable ; whence 
they are commonly divided into two bones, os facrum and 
os coccygis. 
Os J'acrum, is fo called, from being offered in facrifice by 
the ancients, or rather becaufe of its largenefs in refpeCt 
of the other vertebrae. This bone is of an irregular tri¬ 
angular fhape, broad above, narrow below; convex be¬ 
hind, for the advantageous origin of the mufcles that move 
the fpine and thigh backwards; and concave before, for 
enlarging the cavity of the pelvis. Four tranfverfe lines, 
of a colour different from the reft of the bone which are 
feen on its fore-part, are the marks of divilion of the five 
different bones of which it conlifts in young perfons. The 
fore-part of the os facrum, analogous to the bodies of the 
true vertebrae, is fmooth and flat, to allow a larger fpace 
for the contained bowels, without any danger of hurting 
them ; or this flat figure may be owing to the equal pref- 
fure of thefe bowels, particularly of the laft gut. The 
back-part of it is almoft ftraight, without fo large a cavity 
as the vertebrae have ; becaufe the fpinal marrow, now fe- 
parated into the cauda equina, is fmall. The bridges be¬ 
tween the bodies and proceffes of this bone are much thick¬ 
er, and in proportion (horter, than in the former clafs of 
bones. 
There are only two oblique proceffes of the os facrum ; 
one handing out on each fide from the upper part of the 
firft bone. Their plain ereft furfaces face backwards, and 
are articulated witii the inferior oblique proceffes of the 
laft vertebra of the loins, to which each of thefe proceffes 
is connected by a ftrong ligament, which rifes from a fca- 
brous cavity round their roots, where mucilaginous glands 
are alfo lodged. Inftead of the other oblique proceffes of 
this bone, four rough tubercles are to be feen on each fide 
of its furface behind, from which the mufculus facer has 
its origin. The tranfverfe proceffes here are all grown to¬ 
gether into one large ftrong oblong procefs on each fide; 
which, fo far as it anfvvers-to the firft three bones, is very 
thick, and divided into two irregular cavities by a long 
perpendicular ridge. The foremoft of the two cavities 
has commonly a thin cartilaginous (kin covering it in the 
recent fubjeft, and is adapted to the unequal protuberance 
of the os ilium ; and a ftrong ligament connects the cir¬ 
cumference of thefe furfaces of the two bones. The ca¬ 
vity behind is divided by a tranfverfe ridge into two, where 
ftrong ligamentous •firings that go from this bone to the os 
ilium, with a cellular l'ubftance containing mucus, are led- 
ged. The tranfverfe procgfl.es of the two laft bones of the 
os facrum are much fmaller than the former. At their 
buck-part near their edge, a knob and-oblong flat furface 
