Bones of the Lower Extremity. 1 1 7 



The OS ischii (0. T. ischium) (see also Figs. 152, and 154 167) helps by 

 its thicker upper part or body, the corpus ossis ischii, to form the acetabulum. At 

 the anterior margin of this, below the incisura acetabuli, there is not infrequently a 

 small projection, tuberculum olturatorium posterius ; from its posterior margin the 

 strong, sharp spina ischiadica (0. T. spine of ischium) projects backward and some- 

 what medianward. The deep notch between the spina ischiadica and the spina iliaca 

 posterior inferior is called the incisura ischiadica major (0. T. great sacro-sciatic 

 notch) ; a second notch, the incisura ischiadica minor (0. T. lesser sacro-sciatic notch), 

 below the spina ischiadica, between this and the tuber ischiadicum, is flatter and covered 

 with cartilage. 



Extending backward and downward from the body or corpus is the triangularly 

 prismatic ramus superior ossis ischii; its medial surface and the surface directed 

 forward and lateralward is smooth; the surface directed backward and lateralward is rough 

 and much thickened; it forms the tuber ischiadicum (0. T. tuberosity of the ischium). 

 From the lower end of the ramus superior in front the thinner flat ramus inferior 

 ossis ischii (0. T. ascending ramus) goes off, nearly at a right angle; it extends for- 

 ward and upward and fuses with the inferior extremity of the ramus inferior ossis pubis. . 



