ARTICULATIONS. LIGAMENTS. 457 



Osteological Units. The sacrum and ilium. 



Snbdii'isional Parts. Auricular surfaces of the sacrum and ilium. 



Nerve-supply. Superior gluteal, sacral plexus, first and second sacral nerves. 



Blood-supply. Gluteal, ilio-lumbar, and lateral sacral arteries. 



Morphologically, what is that fart of the sacrum that articulates with the 

 auricular part of the ilium / 



It is the result of a peculiar modification of the costal elements of the first 

 three sacral vertebrae. 



Name and locate the ligaments of this articulation. 



(i) Anterior sacro-iliac, from pelvic brim to greater sacro-sciatic foramen ; 

 (2) posterior sacro-iliac, from back of sacrum to iliac crest ; (3) superior sacro- 

 iliac, from sacral base to iliac fossa ; (4) inferior sacro-iliac, from sacrum to pos- 

 terior iliac spine ; (5) interosseous ligament is between the two spines. 



The function of the sacro-iliac ligaments is to bind the sacrum to the ilium. 



Falciform process of the 

 great ligament 



. Tendon of biceps muscle, continuous with 

 the great sacro-sciatic ligament 



FIG. 328. SACRO-SCIATIC LIGAMENTS. (Posterior view. ) 



They are purely of periosteal derivation. The plate of cartilage between the 

 bones may become ossified, just as the ligaments of the vertebral column some- 

 times do. Occasionally, a distinct synovial cavity is found in the center of this 

 cartilage. 



Sacro-ischiatic Ligaments : 



Hozv many ligaments unite the sacrum and ischium ? (Fig. 328.) 



Two ; the common name for these is sacro-sciatic, which is a contraction of 

 the true word for purposes of euphony. The common names are : (i) Greater 

 or posterior sacro-sciatic ligament; (2) lesser or anterior sacro-sciatic ligament. 



Locate the greater ligament. 



The greater or posterior sacro-sciatic ligament is attached above to the mar- 

 gin of the sacrum and coccyx and to the posterior inferior iliac spine ; below to 

 the inner margin of the tuber of the ischium and ascending ramus of the ischium 

 for about two inches. 

 3 



