THE INNOMINATE BONE. 103 



rough creiif, terminating in the projecting sjn'ne. The descending 

 rainus is flat from before backwards ; the superior or ascending ramus 

 becomes prismatic, and increases in thickness as it passes upwards 

 and outwards, and between its posterior and superior surfaces there 

 is prolonged outwards from the spine a ridge which is tlie pubic 

 })ortion of the ilio-pedincal line. The surface in front of this line is 

 covered by the pectineus muscle ; the inferior surface of the ramus 

 presents a deep groove for the obturator vessels and nerve directed from 

 behind forwards and inwards. On the superior surface above the aceta- 

 l)ulum there is a slight elevation, the ilio-peciincal eminence, marking 

 the place of junction of the os pubis and ilium. 



Tlie ischium forms the posterior and inferior part of the os innomi- 

 natum, and bounds the obturator foramen in the lower half of its 

 extent. Superiorly it forms about two-fifths of the acetabulum, infe- 

 riorly it is enlarged in a thick j)rojection, the tuherosiiy, 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 

 yreaf sciatic notch, and is separated from the tuberosity by a short 

 interval, the small .malic notch, against the smooth margin of which 

 glides the teudon of the obturator internus muscle. In front of this, 

 on the external Burftice, a horizontal groove, occupied by the tendon 

 of the obturatur externus muscle, lies l)etween the inferior margin of 

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

 on which the body rests in the sitting posture, presents a rough surface 

 continuous 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 conjoined origin of the biceps and semitendinosus ; 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 acctahulam, 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 

 })osterior and upper part ; while at the opposite side, close to the 

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

 lateral and upi)er parts present a broad bent ribbon-like smooth surface, 

 which articulates with the head of the femur, and in the recent state 

 is coated Avith 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 acetabulum 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 tlie 

 smallest : the non-articular surface belongs chiefly to the ischium. 



The ohturator or thyroid foramen, also Q,-d}\%5i foramen ovale, is internal 

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



