96 BONES OF THE LOWER LIMB. 



wards, and between its posterior and superior surfaces there is prolonged 

 outwards from the spine a ridge called the peclineal line, which is the pubic 

 portion of the ilio-pectineal line. The surface in front of the pectineal 

 line is covered by the pectineus muscle ; the inferior surface of the superior 

 ramus presents a deep groove for the obturator vessels and nerve, directed 

 from behind forwards and inwards. Above the acetabulum the concavity 

 of the border extending from the anterior inferior spine of the ilium to the 

 spine of the pubis is interrupted by a slight elevation, the ilio-pectineal 

 eminence, situated at the junction of the os pubis and ilium. 



The ischium is the posterior and lowest part of the os innominatum, and 

 bounds the obturator foramen in the lower half of its extent. Superiorly it 

 forms about two-fifths of the acetabulum, inferiorly it is enlarged in a thick 

 projection, the tuberosity, and this part, diminishing in size, is continued 

 forwards into the ramus. On its posterior border, behind the acetabulum, 

 a sharp process, the spine, projecting with an inclination inwards, forms the 

 inferior limit of the great sciatic notch, and is separated from the tuberosity 

 by a short interval, the small sciatic notch, against the smooth margin of 

 which glides the tendon of the obturator internus muscle. In front of 

 this, on the external surface, a horizontal groove, occupied by the tendon 

 of the obturator externus muscle, lies between the inferior margin of the 

 acetabulum and the tuberosity. The tuberosifcy, which is the part on which 

 the body rests in the sitting posture, presents a rough surface con- 

 tinuous with the internal margin of the ramus, and on which may be 

 distinguished four impressions, viz., on its upper and broad part two slight 

 hollows, which are placed side by side, the external corresponding to the 

 attachment of the semimembranosus muscle, and the internal to the con- 

 joined origin of the biceps and semitendiiiosus ; and inferiorly two elongated 

 rough elevations, likewise side by side, the external giving attachment to 

 the adductor magnus muscle, and the internal to the great sacro-sciatic 

 ligament : there is likewise along the outer margin a rough elevated line, 

 marking the place of origin of the quadratus femoris muscle. The ramus of 

 the ischium is flattened like the descending ramus of the pubis, with which 

 it is continuous on the inner side of the obturator foramen. 



The acetabulum is a cotyloid or cup-shaped cavity, looking outwards, 

 downwards and forwards, and surrounded in the greater part of its 

 circumference by an elevated margin, which is most prominent at the 

 posterior and upper part; while at the opposite side, close to the 

 obturator foramen, it is deficient, leaving the notch or incisura. Its lateral 

 and upper parts present a broad bent riband-like smooth surface, which 

 articulates with the head of the femur, and in the recent state is coated 

 with cartilage, but the lower part of the cup and the region of the notch are 

 depressed below the level of the articular surface, lodge a mass of fat, and 

 have no cartilaginous coating. Rather more than two-fifths of the aceta- 

 bulum are formed from the ischium, less than two-fifths from the ilium, and 

 the remainder from the os pubis. The iliac portion of the articular surface 

 is the largest, the pubic the smallest : the non-articular surface belongs 

 chiefly to the ischium. 



The obturator or thyroid foramen, also called foramen ovale, is internal 

 and inferior to the acetabulum. In the male it is nearly oval, with the 

 long diameter directed downwards and outwards ; in the female it is more 

 triangular, or narrowed at its lower part. In the recent state it is closed 

 by a fibrous membrane, except in the neighbourhood of the groove in its 

 upper margin. 



