there is any person who could describe it so as to be understood, unless aided by a specimen, or a drawing. I therefore annex the figure (12) that represents an outside view of the bone, near the middle of which is seen a cup-like cavity, l, which receives the round head of the thigh-bone. This socket, or cup, is known as the acetabulum, a word often used in midwifery, though the acetabulum is on the outer surface

does not, as there is no acetabulum within the excavation.

The figure (12) shows the left os innominatum, corresponding with the left half of Fig. 13. On its right is seen the broad expanded iliac portion of it, a, exhibiting its dorsum, bounded above by the crista or crest of the ilium, b, with its anterior superior spinous process, c, on the left, and its anterior inferior spinous process, d, a little lower down. The posterior superior, and the posterior inferior spinous processes are at the bottom of the drawing on the right, e, f, while just behind the acetabulum may be seen projecting backwards the spine of the ischium. At h is the tuberosity of the ischium, and the pubis (at ), whose descending ramus drops downwards to meet and unite with the ascending branch of the ischium. k is the foramen ovale, foramen thyroidean, or obturator foramen; 7, in the bottom of the cup, is the acetabulum; g is the spina ischii.

I now present an inside view of the right os innominatum, in Fig. 13. Here the letter a is placed on the symphyseal end of the os pubis, which, when joined to the left os coxale, makes the pubic symphysis; b is the body of the pubis running backwards to the dotted line on the acetabulum, where it ends; c is the descending ramus pubis, and d the ascending ramus ischii. The letter e is on the plane of the ischium, and ƒ on the iliac fossa or venter; g, the anterior superior spinous process of the ilium; h, its anterior inferior spinous process;

while i and k respectively indicate the posterior superior and the posterior inferior spinous processes of the os ilium. Towards the right side of the drawing may be seen, at 1, the ear-shaped surface that is denominated the auricular facette, which, being covered with fibrocartilage, and united to a

similar facette on the sacrum, composes the sacroiliac joint. The Student will please to note the three dotted lines in the middle of the figure, which indicate the respective limits of pubis, ischium, and ilium in that direction, and he will see that one-fifth of the acetabulum belongs to the pubis; that two-fifths of it

Fig. 13.

are contributed by the ischium; while the upper and outer two-fifths are formed out of the os ilium. By examining these dotted lines, he will learn what parts of the os innominatum belong to each of its three constituent members. In fact, the os innominatum, as has been already seen, was originally three separate bones; which at or about the period of puberty become consolidated by bony anchylosis, or union, into one solid os coxale, hip-bone, or side-bone.

If an os innominatum be taken from a subject under twelve or fourteen years of age, and macerated or boiled in water, it readily separates into three pieces; and the separation takes place because the pieces, in an under age, are not consolidated or become one firm bone. The separation will occur in the acetabular region, where the several pieces are as yet not firmly united by ossific fusion; a union that cannot become complete until the body has acquired such a development as to fit it to undergo the fatigue of gestation, which rarely occurs until the fifteenth year. A bone, taken from the os innominatum of a subject about twelve years old, serves to show the Student the propriety of preserving for the adult skeleton the names of the three separate pieces; for he will learn therefrom that it is very convenient to refer to them in many cases where we desire to direct the attention accurately to a certain point of the pelvis, of which we can then speak, as its ischial, pubic, or iliac portion.

In respect to the acetabular region, or as it is for shortness called the acetabulum, I wish the Student to observe that it is one of the cardinal points in the circumference of the pelvis, and it is highly re

quisite that he should know that the left acetabulum is agreed upon by the profession to be considered as the cardinal point on the female pelvis. There are various cardinal points also upon the foetus, as, for example, the vertex or point of the head, &c. Now, when the vertex, in the head presentation, is found to be at the left acetabulum, it is said to be in the first position; and if it is at the right acetabulum, it is in the second position, and so on; from which it appears that positions are classed numerically, and are, in fact, expressed as numerical relations of some cardinal point upon the child to the cardinal point of the pelvis. Thus, if, in a consultation upon the case, the question should be asked, what is the position? The answer might be, it is the first, or the fifth, or the third, and so forth, which would express the numerical relation of the vertex to the left acetabulum.

The whole pelvis is now seen to consist of a sacrum and coccyx, and of two ossa innominata, and the innominata themselves to consist, in fact, each of a pubis, an ischium, and an ilium. It has been divided into two basins that are called the greater and the lesser, or the superior and the inferior pelvis, that are separated from each other by the inlet, the entrance, the narrows or superior strait.

It is to the hollow of the sacrum that is due the cavity, or, as I am accustomed to call it, the excavation, for the sides and front of that excavation would, if the form depended upon them alone, render the pelvis a cone, which it is not, and indeed far from it, for it is an expanded cavity in which there is abundant room to effect those curious spiral movements of the child that are known as rotation-movements that could not be possible, were it not that the curve of the sacrum gives a sort of balloon-like shape to all that part of the organ that lies between the superior and the inferior straits.

As to the symphysis pubis, we may say that its inner aspect is convex rather than hollow, and as to the two ossa ischia, their inner faces are plane, and not only so, but these planes approach each other as they descend on each side of the basin or canal, so that a body that can lie between the planes at the top can by no means do so at the bottom of them, because at the top the planes are 4 inches asunder, while they are only 4 inches apart at the bottom. The Student will please examine his specimen, or the Fig. 13, to see the shape of this famous plane of the ischium. I am truly desirous that he should get a complete idea of it on account of the influence it has in the mechanism of labors, for the spiral movement of the child is in a good measure due to this very plane, whose form and inclination compel it to rotate or make the spiral turn, which the hollow of the sacrum only allows, but does not compel it to do.

I refer the Student here to a drawing (Fig. 14), which exhibits, on

line eƒ is the axis of the superior strait, not the axis of the pelvis. The artist attempted to represent the axis of the pelvis by the line g k, which cuts all the planes in their centres. This is perhaps a very correct method of representation, but I greatly prefer that of Professor Carus.

Carus's Curve.-A far preferable method of describing and understanding the axis of the pelvis is that proposed by Dr. Carl. Gustav. Carus, Prof. of Midwifery in the Medico-Chir. Acad. of Dresden. His views are stated in his Lehrbuch der Gynækologie, etc., Part I. p. 33, § 44.

Fig. 15.

f

Professor Carus directs that one leg of a pair of compasses should be set in the middle of the posterior edge of the symphysis pubis in a bisected pelvis, as in the figure 15, which I have copied from his plate -the other leg of the compass being opened two and a quarter inches (I propose two inches only), which is half the antero-posterior diameter of the pelvis. A circle may now be drawn downwards, commencing at the plane of the superior strait, and continued through gf, ge, and g a to the point of departure. This is Carus's circle, a segment of which represents, within the excavation, the axis of the pelvis. This

a

a

curve of Carus, which is the bent axis of the pelvis, is an imaginary curved line in coincidence with which the centre of the foetal encephalon moves as it passes from the upper pelvis through the excavation, the inferior strait, and the produced genital aperture, in the act of being born. If the head of the child in a labor should continue to move, after its birth, in the same curve it moved in while within the pelvis, the head would come back to the point of departure at the centre of the plane of the superior strait. The line a b is the axis of the plane of the superior strait, and the line g c is that of the plane of the inferior strait.

Such is Carus's curve, which is the bent axis of the pelvic canal— an important item of midwifery knowledge; one without which a practitioner is incompetent scientifically to deliver a placenta, and far less to extract a child by turning, or to apply and deliver with the forceps or the crotchet. I caution the Student not to fail in understanding this point very perfectly. If he should make himself perfectly familiar with this curve of Carus, I see not how he could make any mistake as to the appropriate direction of his efforts in any act of delivery, whether with the hand alone, or with instruments.

Prof. Dubois, in his Traité Complet de l'Art des Accouchemens, p. 66, after speaking of Carus's curve and commending it as being very simple and at the same time very ingenious, says, it has the fault of giving a not exact idea of the central line of the pelvis; but I consider that for all practical purposes it is far superior to any other, and I believe that the Student who well understands Carus's curve will always act correctly in his manner of adjusting the forceps and other instruments, as well as in operating with them, or with the hand alone, in extracting the head or other parts of the child, because he will clearly apprehend the line in which all movements ought to proceed.

The straits, diameters, planes, axes, and curves of the pelvis are, in an obstetrical regard, related to a certain form, magnitude, and position of the presenting part of the child, which, in its passage through the pelvis, performs certain movements that are spoken of as the mechanism of the labor, and which I shall proceed to explain after I shall have first spoken of the recent pelvis, and of the child in

utero.

The transverse diameter of the superior strait has already been seen to be four and a half inches, and that of the inferior strait only four inches, so that a series of planes superimposed from the lower to the upper strait would be wider and wider as they approach the top, being four and a half at top, and only four inches wide at the bottom.