I have pointed out the ilio-pectineal or ilio-pubic line, and I wish to say that it is the boundary or margin of the superior strait. Let it be occupied with an imaginary superficies, and call that superficies the plane of the superior strait. A line falling perpendicularly upon this plane just midway between the pubis and the sacrum and in the middle of the transverse diameter, is the axis of the superior strait; or, to speak more precisely, it is the axis of the plane of the superior strait. Now, as such perpendicular line does not correspond with the long axis of the trunk of the body, but comes out of the trunk at or near to the umbilicus, and touches the lower end of the sacrum within the pelvis, the plane of the strait is an inclined plane, and it is inclined more or less according to the posture assumed by the patient or the subject. In general, the inclination of this plane is about 50°. If the individual stretches herself upwards, and leans backwards as far as possible, the plane of the strait inclines the more; but if she bows. herself forward, she may bend the trunk over the strait so far as to make the opening wholly lose its inclination, and take an adjustment at right angles to the body. The annexed figure (Fig. 6) represents a

pelvis and spine, with the right lumbar extremities. If the subject lies on the back, with the knee-joint flexed, the plane of the strait (fb) will make, with the axis of the trunk (a), an angle of 140°; or, in other words, the inclination would be 50° below the horizon if the individual were standing up. But if the trunk should be raised up to c, or even carried forwards to d, the inclination would, at c, be 22° 30, and at d nothing at all; for at d the plane would be at right angles to the trunk.

It is very well worth while for the student to note these things, because the ease or difficulty, the celerity or slowness of a labor may depend upon the degree of this inclination, and on nothing else, and

he can understand why a woman who stretches her limbs quite straight out in the bed, and bends her trunk backwards by means of a pillow under the loins, should fail to drive the child's head right through the inlet, and rather force it against the top of the pubis than into the opening; whereas, if she should bend the trunk forwards in a proper manner, she would at once thrust the infant's head through the aperture and drive it down to the very bottom of the excavation. The knowledge of these circumstances, and a vigilant attention to all the details of his duty, enable a practitioner to obviate much suffering for the poor female, tormented with the pains and anxieties that attend upon the parturition of human beings; for the physician may direct the woman to take such a position as to adjust the inclination as he pleases. Indeed, it is an instinctive knowledge that induces almost all women in labor to bow themselves forwards, and a long experience leads the wise matrons, who come to her help, to frequently advise and exhort her to "bend forwards, my dear; bend well forward to the knees."

I shall conclude this part of my subject, by proposing the question: what is the superior strait, and by the answer-the superior strait is the narrow pass from the greater, downwards into the lesser basin or pelvis; it is bounded by the linea ilio-pectinea, and its plane, which is an imaginary superficies, is inclined about 50° in a person standing upright—some authors say 60°; it is 4 inches from front to rear, 43 inches from side to side, and 5 inches in its two oblique diameters; and such are the diameters of the superior strait. I mean to say that a superior strait, possessing these dimensions, ought to be pronounced perfect all the world over, and that while it is true that we meet with many that are larger, we also meet with many that are smaller. A pelvis is large enough when it is as large as the above proposed model. Let the student, however, remember that the larger it is the less the obstruction and difficulty it can give rise to in parturition, and vice versâ.

When two ossa coxalia are correctly adjusted in their places upon a sacrum the pelvis is reconstructed, and we see the pubic arch, the great vacuity above the pubis betwixt the two anterior superior spines of the ilia, the vacuity behind between the posterior parts of the ilia, and a great notch on either side, between the wings of the sacrum and the ossa ischia, and which is called the sacro-sciatic notch. All this, as I before said, gives the idea of a broken basin; but not so in the living subject, for there the upper vacuity is occupied by the tendons of the external oblique muscles, by the recti and pyramidales, and by the abdominal fascia and integuments. On the posterior part, the great basin is made complete by the lower lumbar vertebra which rise

up from the base of the sacrum; by the ilio-sacral and sacro-lumbar ligaments, and by the muscular and tegumentary tissues that complete the round in that direction.

Inferiorly, the pubal arch is closed by the genitalia; the sacrosciatic notches are occupied with ligament and muscle, &c., and the perineal strait is closed by the tissues of the perineum, &c., which thus complete the basin or pelvis, and give it a right to be so called, while it is difficult to see any likeness to a basin in the dried osseous specimen alone.

Having now taken a general view of the pelvis, let us proceed to its analysis, or to an examination of the several bones by whose union it is composed; and this, perhaps, is the only way in which we can correctly compass the important study.

The question that first arises, is: Of how many pieces does a pelvis consist? and the student may properly reply that it is composed of four separate bones, which are: 1st. A sacrum; 2d. A coccyx; 3d. A right, and 4th, a left os innominatum. It would, however, be equally true to say that a pelvis is composed of eight bones, that may be enumerated as follows, videl.: 1. A Sacrum. 2, A coccyx. 3 and 4. A right and left pubis. 5 and 6. A right and left ischium. 7 and 8. A right and left ilium; and if he should choose to say that a coccyx consists of three pieces, he would enumerate ten instead of only four or only eight separate members of a pelvis.

The Sacrum.-The most important bone of the pelvis is the sacrum, because all the others are dependencies of it, and take their character and proportions from it. Indeed, they could not exist without it, as the limb could not exist without the trunk of the tree from which it arises.

Fig. 7.

b

In its origin, a sacrum consists of the elements of five vertebræ, which, in the process of growth, become consolidated or anchylosed into one firm sacrum, and each of the several vertebræ was formed by five points of ossification, that are here represented in Fig. 7, in which a is the original body of the vertebra; c c, the right and the left transverse processes; and bb, the rudiments of the spinous process, which also form the bridge or spinal canal. Even so late as the period of birth, and long after the season of viability of the foetus is passed, the five separate members of each sacral piece are still unconsolidated, and fall apart on being macerated or boiled. But, as the child grows in volume and stature, the bodies of the vertebræ and their transverse and spinous processes

or bridges unite with each other, and the whole of the five vertebræ become fused or soldered, so to speak, into one piece—the bodies making up a sort of central columnar portion-the transverse processes converting themselves by fusion into the bony wings or sides of the sacrum, and the bridges and spinous apophyses becoming the sacral canal and the spinous ridge of the bone. As the transverse processes blend themselves together in regular succession, from top to bottom, they necessarily leave apertures which could not close because the terminal brush of the spinal cord sends out the sacral nerves to make the internal sacral plexus, the origin of the great sciatic nerves that pass outwards through the incisura or sacro-sciatic notch to be distributed on the lower limbs, and thus it is necessary that the sacral holes re

main open.

Fig. 8.

The consolidation of the several sacral pieces has communicated to the sacrum the shape of a three-sided pyramid, whose apex is turned downwards and its base upwards, forming a seat on which the lowest lumbar vertebra rests. The spines or spinous apophyses and the bridges divide the posterior aspect of the sacrum into two smaller faces, while the whole front of the bone makes one large triangular face of four inches to the side (see Fig. 8). This front face, or side of the pyramid, is not plane, but bent or curved so as to make the face quite concave, and give rise to what is called the hollow of the sacrum. The degree of this curve differs in different subjects, but is generally half an inch or more in depth.

In studying the sacrum, it is usual to regard it as having an apex or point (Fig. 8); a base or top; an anterior face or hollow; two posterior faces, each a right-angled triangle; two wings or sides, behind each of which, at the top, is an ear-shaped articulating surface or auricular facette; also ten sacral foramina, or holes for the transmission of internal sacral nerves. These holes are arranged in two upright rows of five holes for each row, which are on each side of the central columnar portion, or bodies of the false vertebræ. The apex terminates in an elliptical convexity, at which the sacrum touches the coccyx at the sacro-coccygeal joint.

At the base or top, is seen an oval-shaped articular surface, which

is the seat upon which the lowest lumbar vertebra rests, and from which, as from a plinth, rises upwards the tall spinal column. This sacro-vertebral facette being cut obliquely backwards causes the

Fig. 9.

sacrum to deviate from the vertical line and retreat or go backwards and downwards behind the spinal column, and thus cause the appearance of a projection in front, overhanging the inlet or superior aperture of the basin, as in the annexed cut (Fig. 9), in which the finger is touching the promontory of the sacrum or sacro-vertebral angle, or projection of the sacrum, for it has all these

names.

The anterior face of the sacrum is nearly an equilateral triangle, of four inches to the sides, and its concavity is deep enough, the foramina being stopped with cement, to hold an ounce or even an ounce and a half of water. It is of great moment that this curve should be just right, as too great or too small a depth is equal to a deformity, and is attended with increased pain, delay, and danger to the laborant. The child, in being born, executes a spiral turn on its long axis, a motion that is known as the rotation of the child, and which, though easy enough in a well-formed hollow, becomes very difficult, or even impossible, in a case where the curve is deficient. Excessive curvature is, also, to be deprecated, as it cannot exist without injury to an antero-posterior diameter.

Both of the posterior faces are convex, very rough, separated from each other by the bridges and spinous process of the sacrum, and provided, like the front, with, each, five sacral foramina for the passage of nerves to the exterior of the pelvis.

The five bodies of the sacral vertebræ have, by anchylosis or fusion, become consolidated into one columnar piece, out of which has been constituted the column or columnar portion of the bone, while the fusion of the ends of the transverse processes together, has converted those processes into wings. It is right to consider the wings as extending along the sides from top to bottom, and not right to limit the idea of wings, to the united transverse processes of the three upper pieces only, as seems to be the intention of Dr. A. F. Hohl, in his new valuable work, Lehrbuch der Geburtshulfe, 1855, p. 30; and in his excellent quarto, Zur Pathol. des Beckens, p. 6.

I said the sacrum was the most important bone of the whole collection, because it may be considered as the basis or parent of all the others. Now, as the sacrum, while growing, touches the innominatum