168 OS PUBIS. 



end of the small leg of the os ischium. The upper surface of 

 each OS pubis is broad, near its junction with the cartilage of 

 the symphysis ; on the internal edge of this surface begins a 

 ridge, which is continued from it along the os ilium, and forms 

 the division between the cavities of the abdomen and pelvis. 

 This ridge is called crista, and including that on the ilium, forms 

 the linea innominata, or ileo-pectinea. On the anterior and ex- 

 ternal edge of this surface of the pubis, at a small distance from 

 the cartilage, is a prominence or process, called the spine. From 

 this process, another ridge, which is much more obtuse, extends 

 to the acetabulum. The upper surface of the pubis, which is 

 included between these ridges, is concave, for the transmission 

 of the crural vessels and nerve, and the psoas and iliacus 

 internus muscles. 



Immediately below the lower ridge, and near the acetabu- 

 lum, a winding notch is made, which is comprehended in the 

 great contiijuous foramen ; but is formed into a hole in the 

 recent subject by a subtended ligament, for the passage of tho 

 posterior crural nerve, and artery, and vein. The internal end 

 of the OS pubis is rough and unequal, for the firmer adhesion 

 of the thick ligamentous cartilage that connects it to its fellow 

 of the other side. The process which goes down from that to 

 the OS ischium is broad and rough before, where the gracilis 

 and upper heads of the triceps adductor femoris have their 

 origin. 



The substance of the os pubis is the same as that of other 

 broad bones. 



Between the os ischium and pubis a very large irregular hole 

 is left, which has been called obturator thyroid. The whole of 

 this foramen, except the notch for the posterior crural nerve, is 

 filled up, in a recent subject, with a strong ligamentous mem- 

 brane, that adheres very firmly to its circumference. From 

 this membrane chiefly, the two external and internal obturator 

 muscles take their rise. The great design of this hole, besides 

 rendering the bone lighter, is, to allow a strong origin to the 

 obturator muscles, and sufficient space for lodging them ; that 

 there may be no danger of disturbing the functions of the con- 



M:i 



