276 THE SKELETON. 



limited, in front, by the margin of the acetabulum ; behind, by the posterior border ; 

 it supports the Pyriformis, the two Gemelli, and the Obturator internus muscles 

 in their passage outward to the great trochanter. The external border forms the 

 prominent rim of the acetabulum, and separates the posterior from the external 

 surface. To it is attached the cotyloid fibro-cartilage. The internal border is 

 thin, and forms the outer circumference of the obturator foramen. The posterior 

 border of the body of the ischium presents, a little below the centre., a thin and 

 pointed, triangular eminence, the spine of the ischium, more or less elongated in 

 different subjects ; its external surface gives attachment to the Gemellus superior, 

 its internal surface to the Coccygeus and Levator ani ; whilst to the pointed 

 extremity is connected the lesser sacro-sciatic ligament. Above the spine is a 

 notch of a large size, the great sciatic, converted into a foramen by the lesser 

 sacro-sciatic ligament ; it transmits the Pyriformis muscle, the gluteal vessels 

 and superior gluteal nerve passing out of the pelvis above the muscles ; the sci- 

 atic vessels, the greater and lesser sciatic nerves, the internal pudic vessels and 

 nerve, and muscular branches from the sacral plexus below it. Below the spine 

 is a smaller notch, the lesser sciatic ; it is smooth, coated in the recent state with 

 cartilage, the surface of which presents numerous markings corresponding to the 

 subdivisions of the tendon of the Obturator internus, Avhich winds over it. It is 

 converted into a foramen by the sacro-sciatic ligaments, and transmits the tendon 

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

 pudic vessels and nerve. 



The tuberosity presents for examination three surfaces : external, internal, and 

 inferior. The external surface is quadrilateral in shape, and rough for the attach- 

 ment of muscles. It is bounded above by the groove for the tendon of the 

 Obturator externus ; in front it is limited by the posterior margin of the obturator 

 foramen, and below it is continuous with the ramus of the bone ; behind, it is 

 bounded by a prominent margin which separates it from the inferior surface. In 

 front of this margin the surface gives attachment to the Quadratus femoris, and 

 anterior to this to some of the fibres of origin of the Obturator externus. The 

 lower part of the surface gives origin to part of the Adductor magnus. The 

 internal surface forms part of the bony wall of the true pelvis. In front it 

 is limited by the posterior margin of the obturator foramen. Behind, it is 

 bounded by a sharp ridge, for the attachment of a falciform prolongation of the 

 great sacro-sciatic ligament ; it presents a groove on the inner side of this for the 

 lodgment of the internal pudic vessels and nerve ; and, more anteriorly, has 

 attached the Transversus perinsei and Erector penis muscles. The inferior surface 

 is divided into two portions an anterior, rough, somewhat triangular part, and a 

 posterior, smooth, quadrilateral portion. The anterior surface is subdivided by _ 

 prominent vertical ridge, passing from base to apex, into two parts ; the outer one 

 gives attachment to the Adductor magnus ; the inner to the great sacro-sciatic 

 ligament. The posterior portion is subdivided into two facets by an oblique 

 ridge ; from the upper and outer facet arises the Semimembranosus ; from the 

 lower and inner, the Biceps and Semitendinosus. 



The ramus, or ascending ramus, is the thin, flattened part of the ischium which 

 ascends from the tuberosity upward and inward, and joins the ramus of the os pubis, 

 their point of junction being indicated in the adult by a rough line. The outer 

 surface of the ramus is rough, for the attachment of the Obturator externus muscle, 

 and also some fibres of the Adductor magnus ; its inner surface forms part of the 

 anterior wall of the pelvis. Its inner 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 descending ramus of the os pubis : 

 to the outer one is attached the deep layer of the superficial perinea! fascia, and to 

 the inner the anterior layer of the triangular ligament of the perinaeum. If these 

 two ridges are traced downward, they will be found to join with each other just 

 behind the point of origin of the Transversus perinsei muscle ; here the two layers 

 of fascia are continuous behind the posterior border of the muscle. To the inter- 



