from the measurements obtained on the living woman by means of calipers.

In the chapters on the pathology of parturition and on the contracted pelvis this subject will be more fully entered into.

The small or true pelvis forms a canal, which runs downwards and backwards. The posterior wall is considerably higher than the anterior, which is constituted by the symphysis pubis. The dimensions of the canal vary in its course, and it is therefore necessary to consider separately different sections of it.

The "inlet" is formed behind by the promontory and the upper and inner margins of the wings of the sacrum, laterally by the iliopectineal line, and in front by the crests and the symphysis of the pubic bones. It has the following diameters:

a. The antero-posterior or conjugate, which is the shortest line connecting the promontory of the sacrum and the symphysis of the pubis,

measures

11 cm. or 4.33 inches.

b. The transverse diameter, between the most dis-
tant points of the ilio-pectineal line 13 cm. or 5.3 inches.
c. The two oblique diameters, between the sacro-

iliac synchondrosis of one side and the ilio-
pubic tuberosity of the other. The right
diameter goes from the right sacro-iliac syn-
chondrosis to the left ilio-pubic tuberosity, and
the left vice versa; each measures

12 cm. or 5 inches.

The ilio-pubic tuberosity marks the inner margin of the iliacus and psoas muscles, and is always distinctly recognisable. The puboiliac synostosis, which has frequently been mentioned as the end of these diameters, is somewhat outside of it, and cannot be recognised in the fully developed pelvis.

For the more exact recognition of a certain class of faulty pelves, a knowledge of the distance between the sacral promontory and the region above the cotyloid cavity is indispensable. This, the sacro-cotyloid diameter, measures in the normal pelvis 8 to 9 cm. or 3.4 to 3.5 inches.

The pelvic cavity varies in width in different parts.

Thus, the widest part lies in a plane which passes through the middle of the symphysis the highest points of the acetabula and the points of junction between the second and third sacral vertebræ. The following diameters are distinguished :

a. The antero-posterior, from the middle of the symphysis to the upper margin of the third sacral vertebra

12 cm. or 4.7 inches.

b. The transverse, between the highest points of

the acetabula in the erect posture. 12 cm. or 4.6 inches.

The narrowest part is in a plane which goes through the inferior angle of the sacrum the spines of the ischium and the apex of the pubic arch. The diameters are—

a. The antero-posterior, from the inferior angle of the sacrum to the apex of the pubic arch

11 cm. or 4.25 inches.

b. The transverse, between the spines of the

ischium

10 cm. or 3.9 inches.

The outlet consists of two triangles the bases of which coincide. Their common base is formed by the line joining the ischial tuberosities. The apex of the anterior triangle is at the vertex of the pubic arch, that of the posterior at the tip of the coccyx. The diameters are

a. The antero-posterior, between the tip of the coccyx and the vertex of the pubic arch

9-9 cm. or 3.3-3.5 inches.

During parturition, however, when the coccyx is pushed backwards, it may be prolonged for rather more than

2 cm. or of an inch.

b. The transverse, between the middle of the ischial tuberosities, equals

11 cm. or 4 inches.

The statements of the normal measurements of the pelvic cavity are very varying, since the individual deviations of the canal are very considerable. The distances given above are obtained from the exact measurements of fifty pelves. The exact result of these measurements is on an average the following:

Ant. pos.

Transv. Right obl.

Left obl. R. s. c. d. L. s. c.d.

Inlet of the cavity... 10-97 cm. 13:41 cm. 12 69 cm. 12:53 cm. 8-71 cm. 8.86 cm. Widest part of the

cavity

.... 12.63

12:41

Narrowest part of the

Nine out of the fifty pelves had the following average measure

Schweighäuser has called attention to the fact that the right oblique diameter is considerably larger than the left, whilst with the sacrocotyloid diameter the reverse is the case. This slight oblique deviation, which probably is a physiological one, may be easily explained by the greater use of the right lower extremity. The weight of the trunk falling especially upon that, the acetabulum is pressed towards that side of the promontory, whilst the right sacro-cotyloid and the left oblique diameters are somewhat shortened.

The oblique diameters of the pelvic cavity and outlet have been omitted, because they depend partly upon the thickness of the soft parts; they do not present any constant measurement.

Till the second half of the sixteenth century obstetricians were entirely ignorant of the conditions of the normal pelvis. The opinion generally prevailed that, during parturition, the joints of the pelvis, more especially that of the symphysis, were separated, and that thus the necessary room was obtained for the

passage of the foetus; also that every pelvis was, in itself, too narrow to allow delivery. Andreas Vesalius (1543) was the first who combated this opinion, and gave an excellent anatomical description of the normal pelvis. He was followed by his pupils. Realdus Columbus (1559) and Julius Cæsar Aurantius (1587), whilst Ambrose Paré (1573), and especially Severinus Pinæus, revived the old teaching of the separation of the joint of the pubic bones during parturition. Heinrich van Deventer (1701), the great Dutch obstetrician, called especial attention to the great importance in midwifery of acquaintance with the pelvis, and commences his Neues Hebammenlicht' with the description of it. Whilst the Englishman Smellie (1751) exhaustively described the pelvis, and was the first to give its correct and accurate measurements, considering it as a whole from an obstetrical point of view, his great rival in France, Levret (1747), made statements which do not accord with the actual conditions. The Dutchman Johann Hurvé (1735) had, however, before this, referred to the measurements of the pelvis. G. W. Stein the elder (1770) followed his teacher Levret, but avoided his errors, and Stein the nephew (1803) described the pelvic spaces, to which description little can be added even at the present time. Luschka corrected the erroneous opinion about the articulation of the pelvic bones, which had until then been considered as constituted by solid cartila⚫ginous wedges. He has shown, moreover, that the sacro-iliac sychondrosis and the pubic symphysis are really joints.

B. THE PROPORTION EXISTING BETWEEN THE SINGLE DIAMETERS OF THE PELVIS

Since the bones of the pelvis, as well as those of the other parts of the body, present very considerable individual differences in shape and size, it is greatly desirable to have a relative method of mensuration, by which the proportion of one of the diameters to all the others can be shown. Thus, from the given measurements pelves of different sizes can be compared with one another with regard to their shape. The conjugate diameter, the one obstetrically of the greatest importance, is taken as the standard, and all the others reduced to that standard. Now, it is easy to calculate the relative value of the sizes from the given absolute measurements. In making these calculations the coccyx is to be disregarded, because, as a movable part, it does not give any constant measurements. The diameters of the pelvic cavity are taken in the widest parts (the distance between the ischial spines is especially to be measured). The antero-posterior diameter of the outlet will be the distance between the symphysis pubis and the inferior angle of the sacrum. The following numbers will then be obtained--the length of the conjugate being equal to 100:

Litzmann, who first applied this method of mensuration, has

obtained somewhat different results. This is probably due to the fact that in the pelves measured by him in Kiel the transverse and oblique diameters greatly preponderated over the anteroposterior. The relative measurements given by him are

C.-INCLINATION OF THE PELVIS AND DIRECTION OF ITS CAVITY

The inclination of the pelvis in the upright position varies, according to Hermann Meyer, even in the same individual, and this variation especially depends upon the degree of rotation or abduction of the thighs. It is the least (40-45°) in very slight rotation inwards, or in moderate abduction of the thighs. By close approximation of the knees, by extreme abduction, as well as by great rotation inwards and outwards, the inclination of the pelvis can be increased up to 100°. In the usual erect posture it is on an average 54.5°.

The dried pelvis is, according to the Brothers Weber, in its normal position in relation to the horizontal line when it is so held that its acetabular cavities look directly downwards; according to H. Meyer the anterior superior spines of the ilium and the pubic tuberosities ought to be in the same vertical plane.

FIG. 1.

The direction of the entire pelvic canal is best determined by a line (Fig. 1, c, d) which is supposed to connect the middle points of the various sections of the pelvic canal. This line is called the axis of the pelvis, or the "guiding line." It is invariable only to the apex of the sacrum; there the direction is changed owing to the mobi lity of the coccyx. Since the sacrum runs almost directly backwards to the third sacral vertebra, if we assume the symphysis also to be straight, the pelvic axis forms a straight line as far as that point. The axis makes an angle with the inlet of about 90°, and its prolongation upwards would approxi

mately pass through the umbilicus; the further course of the pelvic axis, corresponding to the direction of the lower part of the pelvic cavity, is that of a curved line.

The angle which is made by the symphysis pubis with the conjugate diameter is of importance in the mechanism of parturition, as well as in the internal mensuration of the pelvis. In the normal pelvis it measures about 100°.

D. DIFFERENCES BETWEEN THE MALE AND FEMALE PELVIS

Irrespective of the greater density and the more powerful development of the bones of the male in general, the female pelvis is especially

characterised by the shallowness and width of its canal. The iliac bones are less perpendicular, the inlet more spacious, and the cavity funnel-shaped in the male, becomes wider in the female towards the outlet, partly on account of the greater recession of the sacrum and coccyx, partly on account of the greater distance between the ischial spines and the bending outwards of the lower edge of the rami of the pubic arch. The pubic arch, which in the male is an angle of 70-75°, is in the female one of 90-100°. The acetabula are farther apart, and are directed more forwards.

These differences of the female pelvis are caused by the development of the genital organs, which are situated within the true pelvis. By the growth of these the pelvis increases, especially in width. The outward contortion also of the pubic rami is due to the development of the corpora cavernosa, which extend along them.

As a proof that the due development of the pelvic cavity depends upon the female genital organs we may cite the instances of women with arrested mental and physical development; those with undeveloped genital organs always show a general narrowness of the pelvis. Roberts (Journ. de l'Expérience,' 1843, No. 293, p. 99) observed in castrated females amongst the Hindoos uncommonly narrow pubic arches. On the other hand, a pelvis in the Anatomical Museum of Bonn, in which a double uterus had developed, shows a transverse diameter at the brim of 16 cm., or 6·3 inches.

E. DIFFERENCES OF THE PELVIS IN INDIVIDUALS AND RACES

The individual differences of the female pelvis are very great. We rarely meet with pelves which, after a minute examination, can be pronounced perfectly regular. They are almost always asym

metrical.

The shape of the inlet furnishes the best means of recognising the differences. Stein junior and M. J. Weber distinguish four forms of the inlet :

1. That of the obtuse heart of the playing cards (Weber's oval and round oval).

2. That of an ellipse with a greater transverse diameter (this corresponds to Weber's third form, the quadriangular).

3. A rounded form (Weber's second original form).

4. That of an ellipse with a greater conjugate diameter (Weber's wedge-shaped pelvis).

The pelves of the different races are chiefly distinguished by the proportion between the conjugate and the transverse diameters. Corresponding to Stein's fourth form are the pelves of the Bushwomen and of the Malays; in these the conjugate is usually as large as, and only rarely larger than, the transverse diameter. The pelves of the aborigines of America and Australia are almost round, whilst the shape of the pelvis of the African negress resembles that of the Caucasian race. The pelvis of the latter is especially characterised by the greater dimensions of its cavity; the transverse diameter, especially, is very large. This is best exemplified in English women, and then, according to Litzmann's measurements, in the women of Holstein.