Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

14
ANATOMY.
Special however, at its middle than at the extremities, the lower t\\epyriformis, the sciatic nerve and artery, the gluteal ar- Special
outlet of which is diminished by the anterior incurvation of tery, and the internal pudic artery. The second is an ir- Anatomy.
The nel ' ^ .sacr.um an^ coccyx, while the sides are bounded by regular triangular hole, smaller than the upper one, bound-
generally,8 t^le isc^>0_Pubal branches. Before are the inner surfaces of ed above by the anterior ligament, below by the posterior The P^vis
and its di- th? pubal symphysis and branches, corresponding to the one, and laterally by the sinuous hollow between the is-fndTts d’
mansions, urinary bladder ; behind, the pelvic surface of the sacrum, chial spine and tuberosity. Through this aperture the mensionV.'
corresponding to the rectum ; laterally, the thyroid holes, tendon of the obturator internus passes out of the pelvis ;
the inner surface of the ischial-bone and ilio-ischial June- and the external pudic artery and nerve, after bending
tion, and the ischiatic notch, completed by the anterior round the upper ligament, re-enter the pelvis. The third
and posterior sacro-ischiatic ligaments. space is a superficial notch, bounded on the outer or
The upper circumference is very irregular, with its lateral side by the posterior ligament, and on the mesial
plane slightly inclined forwards; larger in the female than side by the sacro-coccygeal bone. It is chiefly occupied
in the male. It presents, behind, the sacro-vertebral ar- by celfular tissue.
ticulation, bounded by a depression indicating the upper The dimensions of this inferior aperture are nearly the
edge of the sacro-iliac synchondrosis; laterally, the two following. The antero-posterior diameter, from the coc-
iliac crests terminating before in the anterior superior cygeal apex to the lower margin of the pubal symphy-
spinous processes; before, the hollow of the iliacus inter- sis, is 3 inches in the male, and 4 inches 6 lines in the
nus and psoas magnus, the ilio-pubal eminence, the hori- female. The transverse diameter between the ischial tu-
zontal branch of the pubal bone, its spine, and lastly its berosities of each side is 3 inches 2 lines in the male, and
symphysis. 4 inches in the female. The oblique diameter, measured
The lower circumference, which corresponds with the from the middle of one of the great sacro-sciatic ligaments
inferior aperture or ano-perineal outlet of the pelvis (am- to the opposite ischial tuberosity, is about 4 inches in the
bitus inferior)^ is directed downwards and backwards, male, and from 41 to 5 in the female. Of these diame-
Bounded behind by the coccygeal bone, and on the sides ters the antero-posterior is most liable to vary, by reason
by the ischial tuberosities, this outlet is thus distinguished of the mobility of the os coccygis; but independent of this,
for three eminences, separated by an equal number of it is always larger in the female than in the male, in con-
notches. The situation of these eminences indicates the sequence of the sacrum being less incurvated, and.de-
limits of the lower pelvic aperture. I he size and dispo- scending more in a straight line. It further appears, that
sition of the notches is inversely to that of the eminences ; in females who have born children the incurvation of the
and their arrangement is such that an eminence is oppo- sacrum is much less than in those who have not.
site to a notch, and conversely. Thus the anterior notch, The direction of the pelvis is not horizontal, nor does it
which is formed by the pubal arch, is opposite to the correspond with that of the trunk. Articulated behind with
sacro-coccygeal eminence behind; and though the ischial the lumbar portion of the spinal column, the axis of which
tuberosities appear opposite to each other in one sense, is inclined considerably forward from the vertical plane,
strictly speaking their plane is each accurately opposed to the pelvis partakes of the same inclination. A horizontal
the opposite sacro-ischial notch. The anterior notch is line drawn from the pubis towards the sacrum passes in
terminated above by an acute angle in the male, in con- general an inch below the tip of the coccyx; and with
sequence of the proximity of the pubo-ischial branches this a line drawn from the pelvis to the upper margin of
which form its sides, but by a rounded arch in the female, the sacrum, representing the plane of the pelvis, makes
by reason of the separation of these branches on each an angle of between 80° and 85°. The sacrum inclines
side. In this notch are situate the generative organs of from the vertical plane about 35°; but the inclination of
both sexes. The lateral notches, which are bounded be- the superior and inferior pelvic apertures varies. An
hind by the sacrum and coccyx, before by the spine and imaginary line drawn from the tip of the coccyx to the
tuberosity of the ischium, are irregular in shape, and are centre of the small pelvis, to represent the axis, cuts the
each subdivided into three portions by the sacro-sciatic line of inclination at an angle of 75°. The most accurate
ligaments, which secure the articulation of the sacrum axis of the pelvis is a line drawn at right angles to the
and coxal bones. The first of these ligaments, the poste- plane of the pelvis as above found.
rior or external, arising from the posterior extremity of The dimensions given above are sufficient to show that
the iliac crest, from the sides and transverse processes of the female pelvis is much more capacious and ample la¬
the sacrum and coccyx by a broad, firm web of fibres, terally than the male. In the female, indeed, it is im-
becoming small and thick at the middle, again expands, portant to remark that the upper region of the coxal
and is inserted into the ischial tuberosity. This ligament bones is more prominent laterally, and hence renders the
corresponds behind to the glutceus maximus, which is part- haunches prominent and rounded, and the outline of the
ly attached to it, before and mesially to the small or an- abdominal aperture more extensive; the sacro-vertebral
terior ligament to which it is united. The small or ante- angle is less prominent, and the sacrum is broader and
rior sacro- sciatic ligament rises, in common with the large less incurvated; the arch of the pubis is wider and less an-
one, from the transverse processes of the sacrum and coc- gular; the ischial tuberosities are more apart, and the
cyx, and adhering to it for half an inch, passes more ho- cotyloid cavities even are at more distance from each
rizontally outwards to the ischial spine, in which it is im- other,—a circumstance which determines the peculiar gait
planted by a broad, thick, fibrous web. Behind, it corre- of the female. The male pelvis, on the contrary, is
sponds at its sacral end, and for an inch from this to the deeper than the female.
posterior ligament, and laterally to the pudic vessels and In the infant the pelvis is small compared with the size
nerve; before, it serves with the posterior to complete of other bones, and of the parts which it is to contain,
the lower circumference of the pelvis. The dimensions of this part, in early life, are indeed so
By these two ligaments the ischiadic notch is in this limited, that not even the urinary bladder can be said to
manner converted into two apertures and a notch. The be contained within it. As puberty approaches, the dis-
first of these is superior, and is bounded above by the ilio- tinctive characters of the male and female pelvis begin to
ischial arch, and below by the small ligament and part of appear. While in both sexes the bones become larger
the posterior or large ligament. Through this hole pass and the cavity more capacious, in the female the addi-