ANATOMY IX A NUTSHELL. 129 



externally at the cotyloid cavity and forms more than one-fifth of it. The su- 

 perior border of this ramus forms the pubic portion of the ilio-pectineal line, 

 running from the spine of the pubis to the internal aspect of the ilio-pectineal 

 eminence. 



The part between the two rami is the body of the os pubis. Its anterior 

 surface is rough and its pelvic surface is smooth. The Pectineus muscle has its 

 origin from the ilio-pectineal line and the triangular surface in front of it. The 

 obturator crest extends from the pubic spine to the acetabulum below the 

 ilio-pectineal line. The obturator groove is on the inferior surface of the 

 ramus behind the outer part of the crest. It is directed from behind forward 

 and inward. 



The pubic crest gives origin to part of the (1) Conjoined tendon, (2) the 

 Pyramidalis and (3) Rectus abdominis. To the pubic spine are inserted (1) 

 Poupart's ligament and the (2) outer pillar of the external abdominal ring. 

 From the front of the pubis, in the angle between the crest and the symphy- 

 sis, arises the (1) Adductor longus muscle, and below this the (2) Adductor 

 brevis and part of the (3) Adductor magnus. Internal to these the (1) 

 Gracilis is attached, and external the (2) Obturator externus. Posteriorly 

 the pubis gives attachment to the (1) Obturator internus; above this is some- 

 times a flat line passing from the upper margin of the obturator foramen to 

 the lower end of the symphysis; the (1) Levator ani muscle is attached to it. and 

 (2) the Obturator and recto-vesical fasciae. 



The Ischium. 



The ischium forms the lower and back part of the innominate bone. It 

 forms a little more than two-fifths of the cotyloid cavity and bounds the obtura- 

 tor foramen below. 



This bone has a body, a tuberosity, and a ramus. The body has three sur- 

 faces and three borders. The surfaces are external, internal and posterior. 

 The borders are also external, internal and posterior. 



The external surface helps form the acetabulum, and this part is smooth 

 and concave. Immediately below the acetabulum is a horizontal groove for the 

 Ten i Ion of the Obturator externus. 



The internal surface forms part of the wall of the true pelvis. In shape it 

 is roughly quadrilateral, also smooth and concave to a small degree. A ridge 

 showing its junction with the ilium is its upper limit. Its anterior limit is its 

 junction with the os pubis and the obturator foramen. Its posterior limit is 

 the anterior margin of the great sciatic notch. Its lower limit is the tuberosity. 

 A part of the Oubtrator internus muscle is attached to this surface. 



Posterior surface is limited in front by the margin of the cotyloid cavity. 

 It is limited behind by the posterior margin of the bone. It is limited above by 

 its connection with the ilium, and it is limited below by the tuberischii. This 

 surface supports the two Gemelli, the Pyriformis and the Obturator internus. 

 Below it presents a pari of the groove tor the Obturator externus. 



The external border is synonymous with that part of the rim of the Aceta- 

 bulum which belongs to the ischium. 



