152 OSTEOLOGY. 



On the inner side of the anterior inferior spinous process is a broad shallow groove, 

 over which passes the Iliacus muscle. 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 processes. The former corresponds 

 with that portion of the posterior surface of the ilium which serves for the 

 attachment of the sacro-iliac ligaments ; the- latter, to the auricular portion which 

 articulates with the sacrum. Below the posterior inferior spinous process is a 

 deep notch, the great sacro-sciatic. 



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

 into a thick and solid portion, the body ; and a thin ascending part, the ramus. 



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

 internal, and posterior. The external surface corresponds to that portion of the 

 acetabulum formed by the ischiurn ; it is smooth and concave above, and forms a 

 little more than two-fifths of that cavity ; its outer margin is bounded by a pro- 

 minent rim or lip, 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 outwards to be inserted into 

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

 the lateral boundary of the true pelvic cavity ; it is broad above, and separated 

 from the venter of the ilium by the linea ilio-pectinea ; narrow below ; its posterior 

 border is encroached upon a little below its centre, by the spine of the ischium, 

 above and below which are the greater and lesser sacro-sciatic notches ; in front it 

 presents a sharp margin, which forms the outer boundary of the obturator foramen. 

 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 above, narrow below where it becomes 

 continuous with the tuberosity ; it is limited, in front, by the margin of the ace- 

 tabulum ; behind, by the front part of the great sacro-sciatic notch. This surface 

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

 their passage outwards to the great trochanter. The body of the ischium presents 

 three borders, posterior, inferior, and internal. The posterior border 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 large size, the great sacro-sciatic, con- 

 verted into a foramen by the lesser sacro-sciatic ligament ; it transmits the Pyri- 

 formis muscle, the gluteal vessels and nerve passing out of the pelvis above this 

 muscle ; the sciatic, and internal pudic vessels and nerve, and a small nerve to the 

 Obturator internus muscle below it. Below the spine is a smaller notch, the lesser 

 sacro-sciatic ; it is smooth, coated with cartilage in the recent state, the surface of 

 which presents numerous markings corresponding to the subdivisions of the tendon 

 of the Obturator internus which 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 this muscle, and the pudic vessels and nerve. The 

 inferior border is thick and broad ; at its point of junction with the posterior, is a 

 large rough eminence upon which the body rests in sitting ; it is called the tube- 

 rosity of the ischium. The internal border is thin, and forms the outer circum- 

 ference of the obturator foramen. 



The tuberosity, situated at the junction of the posterior and inferior borders, 

 presents for examination an external lip, an internal lip, and an intermediate space. 

 The external lip gives attachment to the Quadratus femoris, and part of the Ad- 

 ductor magnus muscles. The inner lip is bounded by a sharp ridge for the attach- 

 ment of a falciform prolongation of the great sacro-sciatic ligament ; 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 perinei, Erector 

 penis, and Compressor urethras muscles. The intermediate surface presents four 



