The anterior border consists of an upper vertical portion formed by the ilitnn, and a lower oblique portion formed by the pubis. It commences above at the anterior superior spine, an inch below which it presents a similar projection called the anterior inferior spino us pro cess (d), the two being separated by a smoothly edged notch (u). Below the inferior spine is another indentation, wider and less deeply marked, and forming part of the overhanging edge of the cavity for the thigh bone, and in which a muscle lies. To this succeeds be low, another rounded, less strongly marked prominence, in which the ilium and pubes are united, called the ilio-pectineal eminence (e). From this point commences the ob lique or inNyard direction of this border, which is for about two inches smooth and rounded for a muscle to glide over, and then presents a fourth well marked, acute, forward projection called the spine of the pubis (f), which is continued by a rough strongly marked ridge, the crest of the pubis (f, g), to the ter mination of this border in an abrupt right angle, the angle of the pubis (g). All these eminences result from the implantation of the tendons of muscles of the leg or abdomen.
The inferior border, composed partly by the pubis, but principally by the ischium, here commences. It is arranged first in a rough, indented, plane, oval, and vertical surface, which in the living bone is united by fibro cartilage to innominate bone of the opposite side, and forms the symphysis of the pubis ;— amount, to grow together (h). The posterior border of this articular surface is often raised into a ridge, projecting backwartls, especially in old persons. Cruveilhier mentions one, observed in a woman who had borne many children, where this was a perfect crest. Be low this point the border assumes a direction tending first downwards and outwards, and then, so.mewhat sharply, curving upwards and backwards. Just below the symphysis it pre sents a sharp, rough, irregular ridge, with a considerable outwardeversion, affording attach ment to strong fasciw and muscles of the leg and perineum, and to the root of the penis. At the most depending part it gradually widens into a very rough, large, elongated, and rounded tuberosity, 3 inches long by 11 broad at its posterior extremity, the tuberosity of the ischium (i). This tuberosity has a general inclination outward ; and along its inner margin, which projects lower than the outer, is a raised ridge for the attachment of the great sciatic liga ment. Upon it are implanted the large pos terior leg muscles, and in the sedentary posi tion the trunk is supported by it. Hence the name of this portion of bone (from Iffxstat ra(butwoc—quod sustineat sedentes), and also its German appellation (Sitzbein or Sitz s t tick).
The posterior border commences above this tuberosity. Its direction is first vertical, and then irregularly horizontal. It is formed by
the ischium and ilium. Above the tuberosity of the ischium is a rounded groove, in the fresh state covered by cartilage, and called the small sciatic or obturator notch (k), over which a muscle glides. Then occurs a sharp pro minent process, turned considerably inwards, giving attachment to a strong lig,ament and some muscles, and called the spine of the ischium (/). Above this the border is thin, rounded' and vertical, becoming gradually much thicker and finally curving sharply backwards and downwards. It thus forms a large notch, the great sciatic, formed principally by the ilium (270. To this succeeds a tapering, elongated, and depending prominence called the posterior in ferior spinous process of the ilium (n), serving for the attachment of ligaments. The border then presents an insignificant rounded notch, with a thin edge; and finally terminates in the superior border at the posterior superior iliac spine, already described.
The external or femoral surface of the os innominatum (fig. 76.) at its upper or iliac portion is directed outwards, backwards, and slightly downwards ; at its central part out wards ; while its pubic and ischiatic or lower part is directed forwards, downwards, and out wards. The iliac portion is broad and fan shaped above, whence this upper portion is called the ala or wing of the ilium. It is convex at its anterior, and concave at its posterior por tion, following the f curve of the crest before mentioned. The concavity is termed by many uriters the external iliac fosse. The convexity is increased by a ridge of thick bone, which passes vertically downwards from the thick ened portion of the crest to the cavity for the thigh bone. At the posterior part of this surface, close to the termination of the crest, is an elongated rough impression of a some what triangular shape, having its base at the superior and inferior posterior spines, and tapering off gradually along the crest for about three inches, which marks the origin of a great muscle—the gluteus maximus, and which may be called the gluteal impression (I). In the middle of this surface is a slizhtiv marked line of an irregular curvairrre, commencing posteriorly at the centre of the great sciatic notch, and, passing upwards and forwards, terminates in the crest a little posterior to the anterior superior spine. This is the superior curved line (2) — (posterior of Cruveilhier). Below this is another line of a like character, the inferior curved line (3) — (the anterior of Cruveilhier); which, commencing an inch be low the:other in the sciatic notch, gradually diverges from it, and terminates anteriorly at the inferior spinous process of the ilium. The surface presents numerous small circular open ings for the admission of the nutritious vessels of the bone, all of which have a direction downwards towards the articular surfaces.