THE HIP BONE 



235 



Obturator interims. Its anterior border projects as the posterior obturator tubercle; 

 from its posterior border there extends backward a thin and pointed triangular 

 eminence, the ischial spine, more or less elongated in different subjects. The 

 external surface of the spine gives attachment to the Gemellus superior, its internal 

 surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed 

 extremity the sacrospinous ligament is attached. Above the spine is a large notch, 

 the greater sciatic notch, converted into a foramen by the sacrospinous ligament; 

 it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, 

 the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, 

 and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of 

 these, the superior gluteal vessels and nerve pass out above the Piriformis, the 

 other structures below it. Below the spine is a smaller notch, the lesser sciatic 

 notch; it is smooth, coated in the recent state with cartilage, the surface of which 

 presents two or three ridges corresponding to the subdivisions of the tendon of 

 the Obturator internus, which winds over it. It is converted into a foramen by 

 the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the 

 Obturator internus, the nerve which supplies that muscle, and the internal 

 pudendal vessels and nerve. 



The Superior Ramus (ramus superior oss. ischii; descending ramus). The 

 superior ramus projects downward and backward from the body and presents 

 for examination three surfaces: external, internal, and posterior. The external 

 surface is quadrilateral in shape. It is bounded above by a groove which lodges 

 the tendon of the Obturator externus; below, it is continuous w r ith the inferior 

 ramus; in front it is limited by the posterior margin of the obturator foramen; 

 behind, a prominent margin separates it from the posterior surface. In front of 

 this margin the surface gives origin to the Quadratus femoris, and anterior to this 

 to some of the fibers of origin of the Obturator externus; the lower part of the sur- 

 iace gives origin to part of the Adductor magnus. The internal surface forms part 

 of the bony wall of the lesser pelvis. In front it is limited by the posterior margin 

 of the obturator foramen. Below, it is bounded by a sharp ridge which gives 

 attachment to a falciform prolongation of the sacrotuberous ligament, and, more 

 anteriorly, gives origin to the Transversus perinsei and Ischiocavernosus. Poste- 

 riorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided 

 into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, 

 madrilateral portion. The lower portion is subdivided by a prominent longitudinal 

 idge, passing from base to apex, into two parts; the outer gives attachment to 

 ;he Adductor magnus, the inner to the sacrotuberous ligament. The upper portion 

 s subdivided into tw r o areas by an oblique ridge, which runs downward and out- 

 vvard ; from the upper and outer area the Semimembranosus arises ; from the lower 

 ind inner, the long head of the Biceps femoris and the Semitendinosus. 



The Inferior Ramus (ramus inferior oss. ischii; ascending ramus). The inferior 

 ramus is the thin, flattened part of the ischium, which ascends from the superior 

 ramus, and joins the inferior ramus of the pubis the junction being indicated in 

 the adult by a raised line. The outer surface is uneven for the origin of the Obturator 

 -.xternus and some of the fibers of the Adductor magnus; its inner surface forms 

 part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly 

 everted, forms part of the outlet of the pelvis, and presents two ridges and an 

 intervening space. The ridges are continuous with similar ones on the inferior 

 ramus of the pubis : to the outer is attached the deep layer of the superficial peri- 

 neal fascia (fascia of Colles), and to the inner the inferior fascia of the urogenital 

 diaphragm. If these tw r o ridges be traced downward, they will be found to join 

 with each other just behind the point of origin of the Transversus perimei; here 

 ;he two layers of fascia are continuous behind the posterior border of the muscle. 

 To the intervening space, just in front of the point of junction of the ridges, the 



