. The science and art of midwifery . O. OBTURATOR FORAMEN. -Outer surface of os Innominatum. ward. The crest of the ilium terminates, front and rear, in bonyprominences, termed respectively the anterior and posterior superior 144 LABOlt. spinous processes. Beneath the upper spines, and separated from themby curved indentations, are two lower, less sharply defined projections,termed the anterior and posterior inferior spinous processes. Behindthe iliac fossa is situated an ear-shaped articular surface, the super-ficies auricularis, which corresponds to the surface of similar namedescribed upon

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. The science and art of midwifery . O. OBTURATOR FORAMEN. -Outer surface of os Innominatum. ward. The crest of the ilium terminates, front and rear, in bonyprominences, termed respectively the anterior and posterior superior 144 LABOlt. spinous processes. Beneath the upper spines, and separated from themby curved indentations, are two lower, less sharply defined projections, termed the anterior and posterior inferior spinous processes. Behindthe iliac fossa is situated an ear-shaped articular surface, the super-ficies auricularis, which corresponds to the surface of similar namedescribed upon the sides of the sacrum. The pubic portion consists of the body and two rami. The bodypresents upon its inner border an oval surface, which articulates withthe pubic bone upon the opposite side. The superior border is fur-nished with a rough crest, terminating in the projecting spine. Theupper, or, as it is usually designated, the horizontal ramus, possessesa ridge, the pecten pubis, extending from the spine and becoming con- CREST.. SUPERFICIESIICULARIS.E. SPINE OF ISCHIUMLESSER SCIATIC NOTCH TUBElROSlTrOF ISCHIUM.Fig. 72. Inner surface of ok innoniinatum. tinuoua with the linea arcuata of the ilium. The linea terminalis, orboundary-line of the pelvic brim, is generally known as the ilio-pec-tineal line, from its sources of origin. Near the junction of the iliumand os pubis is situated a slight elevation, the ilio-pectineal eminence, which, however, according to Luschka, * belongs entirely to the pubichone. The descending ramus helps to bound the obturator foramen, and to form the pubic arch. The ischium completes the lower portionof the OS innoniinatum. It consists of two rami, which, with the ramif the pubic bones, include the obturator foramen. It contributes abouttwo fifth- to the formation of the acetabulum ; from this the descend- iU8chka, Die Antomie des raenschlichen Beckens, p. 86. MECHANISM OF LABOR. 145 ing ramus drops vertically downward, and thence curves forward, a