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the pubis can all be distinguished in front, though overlain by a considerable quantity of fat, whilst the position of the tuberosities of the ischia, when uncovered by the great gluteal muscles in the flexed position of the thigh, can readily be ascertained. In the perineal region the outline of the pubic and ischial rami can easily be determined by digital examination.
Ossification commences in the ilium about the ninth week of intra-uterine life; about the fourth month a centre appears below the acetabulum for the ischium, the os pubis being developed from a centre which appears in front of the acetabulum about the fifth or sixth month. At birth the form of the ilium is well defined; the body and part of the tuberosity of the ischium are ossified, as well as the superior ramus and part of the body of the os pubis. All three parts enter into the formation of the sides of the acetabulum, and by the third year have converged to form the bottom of that hollow, being separated from each other by a triradiate piece of cartilage, in which, about the twelfth year, independent ossific centres make their appearance, which may or may not become fused with the adjacent bones. In the latter case they unite to form an independent ossicle, the os acetabuli, which subsequently fuses with and forms the acetabular part of the os pubis. By the Appears about age of sixteen the ossification of the acetabulum is usually completed, whilst the rami of the ischium and os pubis commonly unite about the tenth year. Secondary centres, seven in number, make their appearance about the age of puberty, and are found in the following situations: one for the anterior inferior iliac spine; one for the ventral two-thirds of the iliac crest and the anterior superior iliac spine which grows backwards, one for the posterior superior iliac spine and dorsal third of the iliac crest which grows forwards-these two unite about the twentieth year; a scale-like epiphysis over the tuberosity of the ischium; a separate epiphysis for the spine of the ischium; (?) a point for the tubercle and another for the angle of the os pubis. Fusion between these and the primary centres is usually complete between the twenty-second and twenty-fifth years. Le Damany states that the proportionate depth of the acetabular cavity at the sixth month of foetal life is greater than at birth. In the third year a rapid increase in its depth again takes place correlated with the assumption of the erect position. Parsons (Journ. Anat. and Physiol. vol. xxxvii. p. 315) regards the ischial epiphysis as the homologue of the hypo-ischium in reptiles, and suggests that the epiphysis over the angle of the pubis may represent the epipubic bone of marsupials.
4th m. of foetal
Appears about 5-6 m. fœtal life Appears about 15 years; fuses 2225 years
Appears about 15 years; fuses 22-25 years
Appears about 15 years; fuses 22-25 years Appears about 12 years
About 12 or 13 years.
FIG. 233.-OSSIFICATION OF THE HIP BONE.
Appears about 18
years Appears about 18 years
Unite about 10 years
The pelvis is formed by the union of the hip bones with each other in front, and with the sacrum behind. In man the dwarfed caudal vertebræ (coccygeal) are curved forwards and so encroach upon the limits of the pelvic cavity inferiorly. The pelvis is divided into two parts by the ilio-pectineal lines, which curve forwards from the upper part of the lateral parts of the sacrum behind to the roots of the pubic tubercles in front. The part above is called the pelvis major, and serves by the expanded iliac fosse to support the abdominal contents; the part below, the pelvis minor contains the pelvic viscera, and in the female forms the bony canal through which at full term the fœtus is expelled.
The pelvis minor is bounded in front by the symphysis pubis in the median plane, and by the body and rami of the os pubis on each side, laterally by the smooth medial surfaces of the ischia and ischial rami, together with a small part of the ilium below the iliac portion of the ilio-pectineal line. Springing from the posterior margin of the ischium are the inturned ischial spines. Behind, the broad curved
FIG. 234.-THE MALE PELVIS SEEN FROM THE FRONT.
anterior surface of the sacrum, and below it, the small and irregular coccyx, form its posterior wall. Between the sides of the sacrum behind, and the ischium and ilium in front and above, there is a wide interval, called the greater sciatic notch, which is, however, bridged across in the recent condition by the sacro-tuberous and sacro-spinous ligaments, which thus convert it into two foramina-the larger above
FIG. 235.-THE FEMALE PELVIS SEEN FROM THE FRONT.
the spine of the ischium, the greater sciatic foramen; the lower and smaller below the spine, called the lesser sciatic foramen.
Apertura Pelvis Superior. The upper opening of the pelvis minor is bounded in front by the symphysis pubis, with the crest of the pubis on each side; laterally by the ilio-pectineal lines; and behind by the sacral promontory. The circumference of this aperture is often called the brim of the pelvis; in the male it is
heart-shaped, in the female more oval. The antero-posterior or conjugate diameter is measured from the sacro-vertebral angle to the symphysis pubis; the oblique diameter from the sacro-iliac joint of one side to the ilio-pectineal eminence of the other; whilst the transverse diameter is taken across the greatest width of the pelvic aperture.
Apertura Pelvis Inferior.-The lower opening is bounded anteriorly by the arcus pubis (pubic arch), formed in front and above by the bodies of the ossa pubis, with the symphysis between them, and the inferior pubic rami below and on either side. These latter are continuous with the ischial rami, which pass backwards and laterally to the ischial tuberosities, which are placed on either side of this aperture. In the median plane behind, the tip of the coccyx projects forward; and in the recent condition the interval between this and the ischial tuberosities is bridged across by the sacro-tuberous ligament, the inferior edge of which necessarily assists in determining the shape of the outlet.
As the anterior wall of the cavity, formed by the symphysis pubis, measures from 1 to 2 inches, whilst the posterior wall, made up of the sacrum and coccyx, is from 5 to 6 inches in length, it follows that the planes of the inlet and outlet are not parallel, but placed at an angle to each other. The term axis of the pelvis is given to lines drawn at right angles to the centres of these planes. Thus, with the pelvis in its true position, when the figure is erect, the axis of the upper opening corresponds to a line drawn downwards and backwards from the umbilicus towards the tip of the coccyx below, whilst the axis of the lower opening is directed downwards and slightly backwards, or downwards and a little forwards, varying according to the length of the coccyx. Between these two planes the axis of the cavity, as it passes through planes of varying degrees of obliquity, describes a curve repeating fairly closely the curve of the sacrum and coccyx.
Position of the Pelvis.-The position of the pelvis in the living, when the figure is erect, may be approximately represented by placing it so that the anterior superior iliac spines and the symphysis pubis lie in the same vertical plane. Under these conditions the plane of the upper opening is oblique, and forms with a horizontal line an angle of from 50 to 60°. The position of the pelvis depends upon the length of the ilio-femoral ligaments of the hip-joint, being more oblique when these are short, as usually happens in women in whom the anterior superior iliac spines tend to lie in a plane slightly in advance of that occupied by the symphysis pubis. In cases where the ilio-femoral ligament is long a greater amount of extension of the hip-joint is permitted, and this leads to a lessening of the obliquity of the pelvis. This condition, which is more typical of men, results in the anterior superior iliac spines lying in a plane slightly posterior to the plane of the symphysis, whilst the angle formed by the plane of the inlet and the horizontal is thereby reduced. Bearing in mind the oblique position of the pelvis, it will now be seen that the front of the sacrum is directed downwards more than forwards, and that the sacral promontory is raised as much as from 3 to 4 inches above the upper border of the symphysis pubis, lying higher than the level of a line connecting the two anterior superior iliac spines. From the manner in which the sacrum articulates with the ilia, it will be noticed that the weight of the trunk is transmitted downwards through the thickest and strongest part of the bone (see Architecture, Appendix A) to the upper part of the acetabula, where these rest on the heads of the femora.
Sexual Differences.-The female pelvis is lighter in its construction than that of the male; its surfaces are smoother, and the indications of muscular attachments less marked. Its height is less and the splay of its walls not so pronounced as in the male, so that the female pelvis has been well described as a short segment of a long cone as contrasted with the male pelvis, which is a long segment of a short cone. The cavity of the pelvis minor in the female is more roomy, and the ischial spines not so much inturned. The pubic arch is wide and rounded, and will usually admit a right-angled set-square being placed within, so that the summit touches the inferior surface of the symphysis pubis, whilst the sides lie in contact with the ischial rami. In the male the arch is narrow and angular, forming an angle of from 65° to 70°. The greater sciatic notch in the female is wide and shallow. The distance from the posterior edge of the body of the ischium to the posterior inferior iliac spine is longer, measuring on an average 50 mm. (2 inches) in the female, as contrasted with 40 mm. (1 inches) in the male. The angle formed by the ischial and iliac borders is more contracted and acute in the male as compared with the
female, in whom it is wider and more open. ately smaller than in the male.
In the female the acetabulum is proportion
The upper opening in the female is large and oval or reniform, as compared with the cribbed and heart-shaped aperture in the male. The sacro-vertebral angle is more pronounced in the female, and the obliquity of the upper opening greater. The sacrum is shorter and wider. The posterior superior iliac spines lie wider apart; the pubic crests are longer; and the pubic tubercles are separated by a greater interval than in man. The outlet is larger; the tuberosities of the ischia are farther apart; and the coccyx does not project forward so much. The curve of the sacrum is liable to very great individual variation. As a rule the curve is more uniform in the male, whilst in the female it tends to be flatter above and more accentuated below. There is a greater proportionate width between the acetabular hollows in the female than in the male. Of much importance from the standpoint of the obstetrician are the various diameters of the pelvis minor. In regard to this it is worthy of note that the plane of "greatest pelvic expansion " extends from the union between the second and third sacral vertebræ behind, to the middle of the symphysis pubis in front, its lateral boundaries on either side corresponding with the mid-point of the medial surface of the acetabulum; whilst the plane of "least pelvic diameter" lies somewhat lower, and is defined by lines passing through the sacro-coccygeal articulation, the ischial spines, and the lower third of the symphysis pubis (Norris). Subjoined is a table showing the principal average measurements in the
two sexes :
11 in., or 282 mm.
7 in., or 176 mm.
10 in., or 273 mm. 93 in., or 250 mm.
7 in., or 180 mm.
in., or 5 in., or 43 in., or 4 in., or
in., or 125 mm.
115 mm. in., or 115 mm. in., or 4 in., or 43 in., or 43 in., or 135 mm. 125 mm. 110 mm.
Growth of the Pelvis. From the close association of the pelvic girdle with the lower limb we find that its growth takes place concurrently with the development of that member. At birth the lower limbs measure but a fourth of the entire body length; consequently at that time the pelvis, as compared with the head and trunk, is relatively small. At this period of life the bladder in both sexes is in greater part an abdominal organ, whilst in the female the uterus has not yet sunk into the small pelvic cavity, and the ovaries and uterine tubes rest in the iliac fossæ. The sacro-vertebral angle, though readily recognised, is as yet but faintly marked. Coincident with the remarkable growth of the lower limbs and the assumption of the erect position when the child begins to walk, striking changes take place in the form and size of the pelvis. These consist in a greater expansion of the iliac bones, necessarily associated with the growth of the muscles which control the movements of the hip, together with a marked increase in the sacro-vertebral angle due to the development of a forward lumbar curve; at the same time, the weight of the trunk being thrown on the sacrum causes the elements of that bone to sink to a lower level between the hip bones. The cavity of the pelvis minor increases in size proportionally, and the viscera afore-mentioned now begin to sink down and have assumed a position within the pelvis by the fifth or sixth year. The extension of the thighs in the upright position necessarily brings about a more pronounced pelvic obliquity, whilst the stoutness and thickness of the ilium over the upper part of the acetabulum is much increased to withstand the pressure to which it is obviously subjected. Coincident with this is the gradual development
of the iliac portion of the ilio-pectineal line, which serves in the adult to separate sharply the pelvis major from the pelvis minor.
This part of the bone is remarkably strong, as will be shown (see Architecture, Appendix A), and serves to transmit the body weight from the sacrum to the thigh bone. The sexual differences of the pelvis, so far as they refer to the general configuration of this part of the skeleton, are as pronounced at the third or fourth month of foetal life as they are in the adult. (Fehling, Ztschr. f. Geburtsh. u. Gynaek. Bd. ix. and x.; A. Thomson, Journ. Anat. and Physiol. vol. xxxiii. p. 359.) The rougher appearance of the male type is correlated with the more powerful muscular development.
The femur or thigh bone is remarkable for its length, being the longest
FIG. 237.-ANTERIOR ASPECT OF PROXIMAL POR-
bone in the body. Proximally the femora are separated by the width of the pelvis. Distally they articulate with the tibia and patellæ. In the military position of attention, with the knees close together, the bodies of the thigh bones occupy an oblique position.
For descriptive purposes the bone is divided into a proximal extremity, comprising the head, neck, and two trochanters; a body; and a distal extremity, forming the expansions known as the condyles.
The caput femoris (head) is the hemispherical articular surface which fits into the acetabulum. Its pole is directed upwards,
FIG. 226. THE RIGHT FEMUR SEEN FROM THE FRONT.
medially, and slightly forwards. A little below the summit, and usually somewhat