MARSUPIALIA. 



295 



five pseudosacral vertebrae may coalesce with each other and 

 with the side of the ischium, converting the pelvis into a long 

 bony tube, the more so as the ilia are also firmly and exten- 

 sively united with the true sacrum. There is usually, especially 

 in Orycferopi/s, a strongly developed 

 " pectineal " tubercle. 



Order Marsuptalia. — In the Ame- 

 rican Opossums {Didelphys), the ilium 

 is a very simple, straight, three-sided 

 rod, thicker at its upper than at its 

 acetabular end, each side being nearly 

 equal in. extent, hollowed, and sharply 

 defined by prominent straight borders. 



In the Kangaroo (Macropiis, Fig. 

 J 08), the three surfaces of the ilium 

 are also well marked and nearly equal ; 

 but the whole bone is curved outwards 

 at the upper end. 



In the Thylacine and Dasyures the 

 ilia are compressed laterally, the ace- 

 tabular and pubic borders meeting 

 above in front, so that the iliac surface 

 is (as in the Carnivora) very narrow, 

 and disappears in the upper half of the 

 bone, the "crest " being formed by the 

 united edges of the sacral and gluteal 

 surfaces ; whereas in the wide, depressed 

 pelvis of the Wombat {P/iascoIoniys), the 

 flattening has taken place in the con- 

 trary direction, and the iliac surface 

 spreads out to form with the gluteal surface behind, a wide, 

 arching, supra-iliac border and crest. 



The ischia and pubes are always largely developed, and the 



Fig. 108. —Ventral surface 

 of innominate bone of 

 Kangaroo (^Macmpus 

 7>injor), i- si snpra- 

 iliac border ; jr.y sacral 

 surface, is iliac sur- 

 face ; (7/' acetabular bor- 

 der ; //' pubic border of 

 ilium ; pt pectineal tu- 

 bercle ; a acetabulum ; 

 ^/{/thyroid foramen ; ti 

 tuberosity of ischium ; 

 .y symphysis ; 711 "mar- 

 supial " bore. 



