igo ELEMENTARY ANATOMY. [LESS. 



The ilium may be a three-sided columnar bone, as in the 

 Kangaroo and many Rodents. The posterior part of the 

 ilium may become anchylosed with the ischium, as is the case 

 in Birds. 



Wherever there is an acetabulum it is in part formed by 

 the ilium. 



FIG. 162. SIDE VIEW OF BONES OF POSTERIOR EXTREMITY OF GREENLAND 

 RIGHT WHALE (Balcenci mysticetus). 



i, ischium \f, femur; /, accessory ossicle, probably representing the tibia. 

 (From Eschricht and Reiuhardt.} 



The ilium may be altogether absent while the ischium is 

 present, as probably in the Cetacea. It is never present 

 without any other pelvic element, except in the Amphisbenian 

 group of Reptiles. 



The prominence of the inferior anterior spinous process 

 in man is exceptional, yet it is exceeded in proportion in 

 some of the Lemuroidea. 



In Marsupial Mammals and Monotremes we find two 

 distinct bones articulated, one on each side of the pre-axial 

 margin of the pubes. They are called "Marsupial bones" 

 and are further noticed below, n. 



The ilio-pectineal eminence is rudimentary in man com- 

 pared with that existing in some other animals even of his 

 own class. Thus in certain Bats it is a very elongated spine 

 projecting upwards from the brim of the pelvis, and it is a 

 very prominent process in the Kangaroo, and sometimes in 

 Marsupials arises from an independent ossific centre. In 

 Reptiles we find a pair of separate bones, usually called 

 the pubes, and meeting generally in a ventral symphysis. 

 They do not, however, so meet in all Reptiles, e.g. the 

 Crocodiles and the Snake Stenostoma. These so-called 



