572 A N A T 
er part of the pudendum and anus. Its life is to fuftain 
and keep the peiiueum in its proper place. 
The anus, .as in the male, has a (ingle ntufcle, and cate 
pair. Sphin-Qcr ani, asrifes from tlte (kin and fat furround- 
ing tire extremity of the reft tun ; and is inferted into the 
white tough l’u-bftance of the perineum ; and into the point 
of the os coccygis. Its ufe is to Unit the panage into the 
Tectum; and., by pulling down the perineum, to aflift jn 
contracting the mouth of the vagina. Levator aui, arifes, 
as in the male, .within the pelvis, and defeends along tire 
inferior part of th.c vagina and ire ft uni. it is inferted into 
the perineum, fphinfter ani, extremity of the vagina, and 
re£tu m. It ferv.es to raife the extremity of the reft urn 
upwards, to contraft the inferior part of the rectum, and 
to aililt in contracting and fupporting' tlte vagina ; and, 
perhaps, by preftiiig on the veins, to 'contribute to tlte dif- 
tenfioh of the. cells of the clitoris and corpus cavernolum 
of the vagina. 
Muscles within the Pelvis. —Of thefe there are two 
pair. i. Obturator intennis, arifes from more than one half 
of the internal circumference of the foramen thyroideum, 
formed by the os pubis and ifehium: its inlide is covered 
by a portion of the levator ani; and appears to be divided 
into a number of fafciculi, which unite and formaround- 
ifh tendon, That palles out of the pelvis, between the pof- 
terior facro-ifchiatic ligament and tuberofity' of the os if¬ 
ehium; where it pafles over the capfular ligament of the 
thigh-bone. It is inferted into the large pit at the root of 
the trochanter major; and ferves to roll the os femoris 
•obliquely outwards. 2. Coccygeus, arifes from the fpinous 
procefs of the os ifehium, and covers the infide of the 
pofterior facro-ifehiatic ligament; and is inferted into the 
extremity of the os facrum, and near the whole length of 
the os coccygis laterally. Its ufe is to fupport and move 
tlte os coccygis forwards, and to tie it more firmly to the 
-facrum. 
Muscles within the Cavity of the Abdomen.— 
Thefe confift of a fingle mufcle, and four pair. The dia- 
phragma , is a broad thin mufcle, which makes a complete 
feptum between the thorax and abdomen, is concave be¬ 
low and convex above; .the middle of it on each fide 
reaching as high within the thorax of the fkeleton as the 
fourth rib ; it is commonly divided into two portions. 1. 
The fuperior or greater mufcle of the diaphragm , arifes, by 
diftinft flelliy fibres, from the cartilago-eniiformis, from 
the cartilages of the feventh, and of all the inferior ribs on 
both Tides. The fibres from the cartilago enfiformis, and 
from the feventh and eighth ribs, run obliquely upwards 
and backwards; from the ninth and tenth, tranfverfely in¬ 
wards and upwards; and, from the eleventh and twelfth, 
obliquely upwards. From thefe different origins the fibres 
run, like radii from the circumference to the centre of a 
circle; and are inferted into a cordifonn tendon, of a con- 
fiderable breadth, which is (ituated in the middle of the 
diaphragm, and in which the fibres from oppofite Tides are 
interlaced. Towards the right fide the tendon is perfora¬ 
ted, by a triangular hole, for the palfage of the vena cava 
inferior; and to the upper convex part of it the pericar¬ 
dium and mediaftinum are connefted. 2. The inferior 
leffer mufcle, or appendix, of the diaphragm, arifes from the 
fecond, third, and fourth, lumbar vertebrae, by eight heads; 
of which two in the middle, commonly called its crura, 
are the longeft, and begin tendinous. Between the crura, 
the aorta and thoracic duft pals; and, on the outfide of 
thefe, the great fympathetic nerves and branches of the 
vena azygos perforate the fhorter heads. The mufcular 
fibres rim obliquely upwards and forwards, and form in 
the middle two flefliy columns, which decollate and leave 
an oval fpace between them for the palfage of the cefo- 
phagus and eighth pair of nerves. It is inferted, by ffrong 
ilelhy fibres, into the p>ofterior part of the middle tendon. 
The diaphragm is the principal agent in refpiration, par¬ 
ticularly in infpiration : for, when it is in aftion, the fibres, 
from their different attachments, endeavour to bring them¬ 
selves into a plane towards the middle tendon, by which 
O M Y. 
the cavity of the thorax is enlarged, particularly at the 
fides, where the lungs are chiefly (ituated ; and, as the 
lungs mud always be contiguous to the infide of the tho¬ 
rax and upper fide of the diaphragm, the air rulhes into 
them, in order to fill up the increafed fpace.- This- mufl 
cle is allified by the two rows of intercoftals, which elevate 
the ribs, and the cavity of the thorax is more enlarged. 
In time of violent exercife, or whatever caufe drives the 
blood witli unufual celerity towards the lungs, the pecto¬ 
ral mufcles, the ferrati antic! majores, the ferrati poflici 
fuperiores, and fcaleni mufcles, are brought Into aftion. 
And, in laborious infpiration, the mufcles vs Inch arife from 
the tipper part of the thorax, when the parts into which 
they are inferted are fixed,'likewife aflift. In expiration, 
tlte diaphragm is relaxed and pulhed up by the prefTure of 
the abdominal mufcles upon the vifeera of the abdomen; 
and at the fame time that they prefs it upwards, they alfo, 
together with the fterno-coftales and ferrati poflici inferio- 
ries, pull down the ribs, and are aflifled in a powerful 
manner by the elafticify of the cartilages-that join the ribs 
to tine fternuni; by which the cavity \of the thorax is dimi- 
nilhed, and tire air fuddenly puftfed out of the lungs: and, 
in laborious expiration, tlie quadrati lumborum, facro- 
lmnbales, and longilfimi dorfi, concur in pulling down 
the ribs. 
The four pair are, 1. Quadratus lumborum, arifes from the 
pofterior part of the fpine of tlte os ilium; and is inferted in¬ 
to the tranfverfe proceffes of all the vertebrae of the loins, 
into the laft rib near the f pine, and by a fmall tendon into 
the fide of the laft vertebra of the back. Its ufe is to move 
the loins to one fide, pull down the laft rib, and, when 
both aft, to bend the loins forwards. 2. Pfoasparvus, au¬ 
ks from tlte (ides of the two upper vertebral of the loins, 
and fends off a final! long tendon, vv hich ends thin and 
fiat, and is inferted into the brim of the pelvis, at the 
junction of the os ilium and pubis. Its ufe is to aflift the 
pfoas magnus in bending the loins forwards; and, in cer¬ 
tain pofitions, to allift in raifing the pelvis. 3. Pfoas mag- 
nits, arifes from the fide of the body, and tranfverfe pro¬ 
cefs of the laft vertebra of the back; and, in the fame 
manner, front all thofe of the loins, by as many diftinft flips. 
It is inferted into the trochanter minor of the os femoris ; 
and into that bone a little below the fame trochanter. Its 
life is to bend the thigh forwards ; or, when the inferior 
extremity is fixed, to aflift in bending the body. 4. Itiacus 
internus, arifes from the tranfverfe procefs of the laft ver¬ 
tebra of the loins, from all the inner lip of the fpine of 
the os ilium, from the edge of that bone between its an¬ 
terior fuperior fpinous procefs and the acetabulum, and 
from moft of the hollow part of the ilium. It joins with 
the pfoas magnus, where it begins to become tendinous; 
and is inferted along with it. Its ufe is to aflift the pfoas 
in bending the thigh, and to bring it direftly forwards. 
Muse les on the anterior part of the Thorax.—• 
Thefe may be divided into two layers. The firft layer con- 
fifts of one mufcle, named peEloralis major. It arifes from 
tlie cartilaginous extremities of the fifth and fixth ribs; 
from almoft the whole length of the fternum, and from 
near half of the anterior part of the clavicle. It is infert¬ 
ed, by two broad tendons, which crofs each other at the 
upper and inner part of the os humeri, above theinfertion 
of the deltoid mufcle, and outer fide of the groove for 
lodging the tendon of the long head of the biceps. Its 
ufe is to move the arm forwards, and obliquely upwards, 
towards the fternuni. 
The fecond layer confifts of three mufcles : i.Subcla- 
vius, arifes from the cartilage that joins the firft rib to the 
fternum; and is inferted into the inferior part of the cla¬ 
vicle; .and ferves to pull the clavicle downwards and for¬ 
wards. 2. PeEloralis minor, arifes from the upper edge of 
the third, fourth, and fifth, ribs; and is inferted into the 
coracoid procefs of the fcapula. It ferves to bring the 
fcapula forwards and downwards, or to raife the ribs up¬ 
wards. 3. Scrratus magnus, arifes from the nine fuperior 
ribs, by an equal number of flefliy digitations, refembling 
