120 



COMPARATIVE ANATOMY 



(Carinatce). The preacetabular portion of the ilium extends for- 

 ward for a considerable distance, and a number of vertebrae 

 belonging to other than the true sacral region become secondarily 

 connected with the ilium {see p. 48). The acetabulum is per- 

 forated, and the pars acetabularis (p. 119) forms a spinous process. 

 The elements of the pelvis usually become anchylosed together. 

 The pubis meets its fellow in the middle line only in Struthio, 

 and the ischium only in Rhea. 



Mammals. — The elements of the pelvis here remain separated 

 for a long time by cartilage, but later they become fused together. 

 The pubis always takes less part in the formation of the aceta- 

 bulum than do the other two bones, and may be more or less 

 entirely shut out from it by an ossification of the pars acetabularis, 

 which subsequently unites with either the ilium, ischium, or 

 pubis (Figs. 98 and 99). This acetabular hone is especially well 

 developed in the Mole, in which it shuts the ilium, as well as the 

 pubis, out of the acetabulum : the latter is perforated in Mono- 

 tremes. The angle between the axes of the ilium and sacrum is 

 large in Ornithorhynchus, and more acute in other Mammals. 



The original type with both pubic and ischiatic symphyses is 

 seen in Monotremes, Marsupials (Fig. 100), many Eodents, In- 

 sectivores and Ungulates. In many other Insectivores, in Carnivores, 

 and more particularly in the Primates, the ischia no longer meet 

 below. The greatest amount of variety in the form of the pelvis 



Fig. 98. — Extbenal View op the 

 Right Halp or the Human 

 Pelvis. (From the outer side.) 



The three bones — ilium (//), ischium 

 {In), and pubis (P)— are shown dis- 

 tinct from one anotlier in the 

 acetabuhim. Fo, obturator for- 

 amen. 



Fig. 99.— Uiagkam showing the 

 Relations of the Paes Aceta- 

 bularis (in Viverra a'l-etta). 



J, ilium ; Jf:, ischium ; P, pubis j 

 A, acetabular bone ; Ac, aceta- 

 bulum. 



in any one order^ is seen in Insectivores, in some of which (e.g.. 

 Mole), as well as in most Bats, there is no symphysis pubis. The' 

 obturator foramen is always surrounded by bone. 



