54 § A N A 1 
give t ife to two ftrong ligaments which are extended to the 
os ifchium ; and are therefore called facrociatic. 
The fpinal procelfes of the three uppennoft bones of the 
os facrum appear fhort, (harp, and almod eredt, while the 
two lower ones are open behind; and fometimes a little 
knob is to be feen on the fourth, though generally it is bi¬ 
furcated, without the two legs meeting into a fpine; in 
which condition alfo the fir ft is often to be feen; and 
fometimes none of them meet, but leave a firms, or rather 
fo'Ja, infiead of a canal. The mufculus latiffimus and 
longiiugnus dorfi, facro-lumbalis, and glutaeus maximus, 
have part of their origins from thefe fpinal procefies. At 
the root of each oblique procefs of this bone, the notch is 
confpicuoiis ; by which, and another (imilarone in the lad 
vertebra of the loins, a padage is left for the twenty- 
fourth fpinal nerve; and., in viewing the os facrum, either 
before or behind, four large holes appear in each (ide, in 
much the (ame height as where the marks of the union of 
its feveral bones remain. Some of the larged nerves of 
the body pafs through the anterior holes; and fuperficial 
grooves, running outwards from them, in different direc¬ 
tions, (hew the courfe of thefe nerves. From the inter¬ 
vals of thefe grooves, the pyriformis nmfcle chiefly rifes. 
The holes in the back-part of the bone are covered by 
membranes which allow finall nerves to pafs through them. 
The fubdance of the os facrum is very fpongy, without 
any confiderable folid external plates, and is lighter pro¬ 
portionally to its bulk than any other bone in the body; 
tut it is feeured from injuries by the thick mufcles that 
cover it behind, and by the drong ligamentous membranes 
that clofely adhere to it. As this is one of the mod re¬ 
markable indances of this fort of defence afforded a foft 
weak bone, we may make this general obfervation: That, 
wherever we meet with fuch a bone, one or other or both 
thefe defences are ufed; the fird to ward off injuries, and 
the fecond to keep the fubftance of the bone from yield¬ 
ing too ealily. This bone is articulated above to the lad 
vertebra of the loins, in the manner that the lumbar ver¬ 
tebrae are joined. The articulation of the lower-part of 
the os facrum to the os coccygis, feems well enough adapt¬ 
ed for allowing confiderable motion to this lad bone, were 
it not much confined by ligaments. Laterally, the os fa¬ 
crum is joined to the olfa ilium by an immoveable fyn- 
ehondrofis, or what almod deferves the name of a future. 
For the cartilaginous crud on the furface of the bones is 
very thin; and both their furfaces are fo fcabrous and un¬ 
equal, as to be indented into each other; which makes fuch 
a drong connection, that great force is required to fepa- 
r.ite them, after all the mufcles and ligaments are cut. 
Frequently the two bones grow, together in old people. 
The ufes of the os facrum are, to lerve as the common 
bafe and ftipport of the trunk of the body, to guard the 
nerves proceeding from the end of the fpinal marrow, to 
defend the back-part of the pelvis, and to afford fufficient 
origin to the mufcles which move the trunk and thigh. 
The os coccygis, or rump-bone, is that triangular chain of 
bones depending from the os facrum ; each bone becoming 
fmaller as they defeend, till the lad ends almod in a point. 
The os coccygis is convex behind, and concave before; 
from which crooked pyramidal figure, which was thought 
to refemble a cuckow’s beak, it has got its name. This 
bone confids of four pieces in people of middle age. In 
children, almod the whole of it is cartilage. In old fub- 
jedts, all the bones are united, and become frequently one 
continued bone with the os facrum. The highed of the 
four hones is the larged, with fhoulders extended farther 
to each fide than the end of the os facrum. From the 
back of that bulbous part, called its fiioulders, a procefs 
often rifes up on each fide, to join with the bifurcated 
lpine of the fourth and fifth hones of the os facrum, to 
form the bony bridge mentioned in the defeription of the 
os facrum. Sometimes thefe fhoulders are joined to the 
(ides of the fifth bone of the os facrum, to form the hole 
in each fide common to thefe two bones, for the paffage 
©f the twenty-ninth pair of fpinal nerves. Immediately 
O M Y. 
below the fiioulders of the os coccygis, a notch may be 
remarked on each fide, where the thirtieth pair of the fpi. 
nal nerves pafles. 
The three lower bones gradually become fmaller, and 
are fpongy ; but are drengthened by a drong ligament 
which covers and connects them. Their ends, by which 
they are articulated, are formed in the fame manner as thofe 
of the fird hone. To the (ides of thefe hones the coccy- 
gsei mufcles, and part of the levatores ani, and of the 
glutasi maximi, are fixed. The fubdance of thefe bones 
is very fpongy, and in children cartilaginous; there being 
only a part of the fird bone ofiified in a new-born infant. 
Since therefore the intedinum reftumof children is not fo 
firmly fupported as it is in adults, this may be one reafon. 
why they are more fubject to a procidentia ani than old 
people. From the defeription of this bone, we fee how 
little it refembles the vertebra;; fince it feldom has pre¬ 
cedes, never has any cavity for the fpinal marrow, nor 
holes for the paflage of nerves. Its connection hinders it 
from being moved to either fide ; and its motion back¬ 
wards and forwards is much confined : yet, as its ligaments 
can be dretched by a confiderable force, it is of great ad¬ 
vantage in the excretion of the faeces alvinae, and much 
more in child-bearing, that this bone fnould remain move- 
able; and the right management of it, in delivering wo¬ 
men, may be of great benefit to them. The mobility of 
the os coccygis diminifhing as people advance in age, es¬ 
pecially when its ligaments and cartilages have not been 
kept flexible by being dretched, is probably one reafon 
why the women, who are old maids before they marry, 
have generally difficult parturition. 
The fecond part of the trunk of the (keleton, viz. the 
pelvis, is the cylindrical cavity at the lower part of the 
abdomen formed by the os facrum, os coccygis, and ofla 
innominata. The ojfa innominata are two large broad bones, 
which form the fore-part and (ides of the pelvis, and the 
lower part of the fides of the abdomen. In children, each 
of thefe bones is evidently divided into three; which are 
afterwards fo intimately united, that hardly the lead mark 
of their former feparaticn remains. They are neverthelefs 
deferibed as confiding each of three bones, viz. the os ili¬ 
um, ifchium, and pubis. 
The os ilium, or haunch-bone, is fituated highed of the 
three, and reaches as far down as one third of the great 
cavity into which the head of the thigh-bone is received. 
The external fide of this bone is unequally convex, and 
is called its dorjum ; the internal concave furface is by fome 
authors (but improperly) named its cojla. The femicir- 
ctilar edge at the highed part of this bone, which is tip¬ 
ped with a cartilage in the recent fubjedt, is named the 
fpine, into which the external or defeending oblique muf- 
cle of the abdomen is inferted ; and from it the internal 
afeending oblique, and the tranfverfe mufcles of the bel¬ 
ly, with the glutasus maximus, quadratus lmnborum, and 
latiffimus dorli, have their origin. From the anterior fpinal 
procefs, the fartorious and fafcialis mufcles have their rife, 
and the outer end of the doubled tendon of the external 
oblique mufcle of the abdomen, commonly called Fallo¬ 
pius's or Poupart’s ligament, is fixed to it. The infide of 
the poderior fpinal procefs, and of part of the fpine for¬ 
ward from that, is made flat and rough where the facro- 
lumbalis and longiffimus dorfi rife ; and to its outfide are 
fixed ligaments extended to the os facrum and tranfverfe 
proceffes of the fifth and fourth vertebra: of the loins. 
Between the fides of the os ilium, and the drong ligament 
that is dretched over from the os facrum to the (harp- 
pointed procefs of the os ifchium of the recent fubjedl, a 
large hole is formed, through which the mufculus pyri- 
fonnis, the great fciatic nerve, and the poderior crural 
veflels, pafs, and are protedled from compredion. 
The external broad fide or dorfum of the cs ilium, is a 
little hollow towards the fore-part; farther back, it is as 
much raifed; then is confiderably concave; and, lafily, it 
is convex. Thefe inequalities are occafioned by the ac¬ 
tions of the mufcles that are fituated on this furface. 
j From 
