1 80 ELEMENTAL Y ANA TOM Y. [LESS. 



process called the spine of the ischium. Below this, and below 

 the socket, the bone contracts and then expands again, the 

 expansion having a rough prominent surface, which is called 

 the tuberosity of the ischium ; and it is the two tuberosities (of 

 the two ossa innominata) which support the body when in a 

 sitting posture. Just below the tuberosity, the ischium sends 

 forth a flat band of bone (the ascending ramus), which, curv- 

 ing forwards and upwards, meets the descending bony band 

 of the pubis spoken of above. 



The socket for the thigh-bone (which has been so often 

 referred to) is called the acetabulum* or cotyloid* cavity. It 

 has a prominent rim, except at the inner and lower part 

 where the rim is interrupted by a notch (the cotyloid notch). 

 There is no perforation in the acetabulum, but its surface just 

 within the notch is depressed, the depression affording attach- 

 ment to the very strong ligamentum teres (or round ligament) 

 which goes from it to the head of the thigh-bone. 



Enclosed by the ilium, ischium, and pubis, there is in each 

 os innominatum a vacant, oval space called the obturator^ 

 foramen, one such being placed on each side of the pubic 

 symphysis. 



The deep concavity, in the posterior border, between the 

 posterior inferior spinous process of the ilium and the spine 

 of the ischium, is called the greater ischiatic notch; the 

 smaller concavity, between the spine of the ischium and the 

 tuberosity of that bone, is called the lesser ischiatic notch. 



The two ossa innominata, together with the sacrum, form 

 what is called the pelvis, or basin-shaped cavity which sup- 

 ports the viscera. 



The internal surface of each os innominatum is divided 

 into two parts by a prominent line running upwards and 

 backwards from the upper part o'f the pubis to the sacrum. 



The width from side to side of the pelvis is but rarely ex- 

 ceeded by its depth from behind forwards, but exceeds the, 

 greatest vertical extent of the ossa innominata. 



A strong ligament connects the tuberosity of the ischium 

 with the sacrum, the coccyx, and the posterior margin of the 

 ilium. This is called the great sacro-sciatic ligament. Another 

 ligament goes from the sacrum and coccyx to the spine of 

 the ischium. This is termed the small sacro-sciatic ligament. 



1 From its resemblance to an ancient vinegar cup. 



2 From KOTtiXr), a cup. 



3 Because if surrounds the obturator membrane which closes up part of the 

 pelvic cavity. 



