xvii.] GENERAL CHARACTERS. 315 



This may be called the sacral surface (see Figs. 114, and 

 Ir 5. P- 3 X 7; and 116, ss, p. 325.) Another is directed 

 mainly forwards, and may be called anterior or iliac (M), as 

 it gives origin to the iliacus muscle. The third is posterior 

 or gluteat (gs), as it gives origin to the gluteal muscles. 



Of the borders one is external or acetabular (ab\ as it 

 ends below at the margin of the acetabulum ; another is 

 antero-internal or pubic ( pb), and the third is postero-internal 

 or ischial (ib) t so called because they end below by joining 

 the pubis and the ischium respectively. 



The innominate bone is always placed more or less 

 obliquely to the vertebral column, the upper or iliac end 

 inclining forwards, and the lower or ischio-pubic end turning 

 backwards, contrary to the usual direction of the scapular arch. 

 In order to give still greater stability and fixity to the pelvic 

 girdle, and to incorporate it more completely for mechanical 

 purposes with the vertebral column, there is, in addition to 

 the articulation between the ilium and true sacral vertebrae, 

 a very strong double ligamentous union between the ischium 

 and the side of the anterior caudal or pseudo-sacral vertebrae, 

 constituting the greater and lesser sacro-sciatic ligaments, 

 which are replaced in some Mammals (as most of the Eden- 

 tata) by a complete bony union. 1 



The two innominate bones, together with the sacrum, 

 constitute the pelvis, a complete circle of bone, or rather a 

 short tube. This has two outlets : an anterior (sometimes 

 called inlet or brim) bounded by the inferior surface of the 

 first sacral vertebra above, by the pubic borders of the 

 ilia laterally, and by the anterior borders of the converging 

 pubic bones, meeting at the symphysis below ; and a 



1 Practically, though not morphologically, the pelvis is a part of the 

 trunk or axial skeleton. The functions of the hind limb in propelling 

 and raising the body necessitate that it should be so. 



