THE OS lyyOMISATUM. 275 



the formation of the true pelvis, and which gives attachment to part of the Obturator 

 internus muscle. Behind the iliac fossa is a rough surface divided into two por- 

 tions. an anterior and a posterior. The anterior or auricular portion, so called from 

 its resemblance in shape to the ear, is coated with cartilage in the recent state, and 

 articulates with a surface of similar shape on the side of the sacrum. The posterior 

 portion is rough, for the attachment of the posterior sacro-iliac ligaments and for 

 a part of the origin of the Erector spinae. 



The crest of the ilium is convex in its general outline and sinuously curved, 

 being bent inward anteriorly, outward posteriorly. It is longer in the female 

 than in the male, very thick behind, and thinner at the centre than at the extrem- 

 ities. It terminates at either end in a prominent eminence, the anterior superior 

 and pn!ttt_-r!"'f sup .//-/ xpinous process. The surface of the crest is broad, and 

 divided into an external lip, an internal lip, and an intermediate space. To the 

 external lip is attached the Tensor vaginae femoris, Obliquus externus abdominis, 

 ami Latissimus dorsi, and by its whole length the fascia lata ; to the space between 

 the lips, the Internal oblique : to the internal lip, the Transversalis, Quadratus 

 lumborum, and Erector spinte, the Iliacus. and the fascia iliaca. 



The anterior border of the ilium is concave. It presents two projections, 

 separated by a notch. Of these, the uppermost, situated at the junction of the 

 and anterior border, is called the anterior superior spinous process of the ilium, 

 the outer border of which gives attachment to the fascia lata and the origin of 

 the Tensor vaginae femoris; its inner border, to the Iliacus; whilst its extremity 

 affords attachment to Poupart's ligament and the origin of the Sartorius. Beneath 

 this eminence is a notch which gives attachment to the Sartorius muscle, and 

 across which passes the external cutaneous nerve. Below the notch is the anterior 

 ///r, //// *].iitt<>, I* ],,:. x*. which terminates in the upper lip of the acetabulum ; it 

 gives attachment to the straight tendon of the Rectus femoris muscle and the 

 ilio-femoral ligament. On the inner side of the anterior inferior spinous process 

 is a broad, shallow groove, over which passes the Iliacus muscle. This groove is 

 bounded internally by an eminence, the ilio-pectineal, which marks the point of 

 union of the ilium and os pubis. 



The posterior border of the ilium, shorter than the anterior, also presents two 

 projections separated by a notch, the posterior superior and the posterior inferior 

 spinous pro>->.-**>-*. The former corresponds with that portion of the posterior 

 surface of the ilium which serves for the attachment of the oblique portion of the 

 sacro-iliac ligaments and the Multifidus spin* ; the latter to the auricular portion 

 which articulates with the sacrum. Below the posterior inferior spinous process 

 is a deep notch, the great sciatic or ih'o-sciatic. 



The Ischium forms the lower and back part of the os innominatum. It is 

 divisible into a thick and solid portion, the body ; a large, rough eminence, on which 

 the body rests in sitting, the tuberosity ; and a thin, ascending part, the ramus. 



The body, somewhat triangular in form, presents three surfaces, external, 

 internal, and posterior ; and three borders, external, internal, and posterior. The 

 mil * ii rf !'' corresponds to that portion of the acetabulum formed by the 

 ischium : it is smooth and concave, and forms a little more than two-fifths of 

 the acetabular cavity : its outer margin is bounded by a prominent rim or lip, 

 the external border, to which the cotyloid fibro-cartilage is attached. Below the 

 acetabulum. between it and the tuberosity, is a deep groove, along which the tendon 

 of the Obturator externus muscle runs as it passes outward to be inserted into 

 the digital fossa of the femur. The internal surface is smooth, concave, and enters 

 into the formation of the lateral boundary of the true pelvic cavity. This surface 

 is perforated by two or three large, vascular foramina, and affords attachment to 

 part of the Obturator internus muscle. The posterior surface is quadrilateral in 

 form, broad and smooth. Below, where it joins the tuberosity, it presents a groove 

 continuous with that on the external surface, for the tendon of the Obturator 

 externus muscle. The lower edge of this groove is formed by the tuberosity of the 

 ischium. and affords attachment to the Gemellus inferior muscle. This surface is 



