THB RABRIT. 



75 



DORSAL 



AWT"! 



Fig. 40. DIAGRAM OF ROTATION OF 

 PELVIC GIRDLE. 



12. The Pelvic or Hip-girdle (fig. 41) differs from the 

 pectoral in practically all air-breathing vertebrates, by being 

 articulated with the vertebral column (sacral vertebrae). 

 The pelvic girdle is much 

 more complete than the 

 pectoral, but it has under- 

 gone a backward rotation 

 from its primitive position 

 (fig. 40), so that the dorso- 

 lateral bone (here called 

 ilium) which articulates 

 with the sacrum comes to 

 lie parallel with the ver- 

 tebral column instead of 

 vertically ; the antero-ventral (pubis) comes to be entirely 

 ventral ; and the postero-ventral (ischium) comes to be 



postero-dorsal, and does 

 not meet its fellow in 

 the middle line at all. 

 The hollow for the 

 articulation of the limb 

 is called the acetabulum ; 

 at its ventral border 

 an extra little bone is 

 found, (possibly of the 

 nature of an epiphysis) 

 called the cotyloid. 

 The large space between 

 the pubis and ischium 

 is called the obturator 

 fenestra a fenestra 

 meaning a portion of 

 the skeleton consisting 

 of membrane (connec- 

 tive tissue) only, as 



distinguished from a foramen, which is a hole through 

 which something passes ; there is an obturator foramen 

 at one point in the fenestra where a nerve passes 



Fig. 41. PELVIC GIRDLE AND SACRAL 

 VERTEBRA. 



through. The distinction between a foramen and a 

 fenestra is important, but in the dried skeleton, where 



