196 ELEMENTS OF OENITHOLOGT. 



The ischium is the bone which forms the hinder margin of the 

 acetabulum, and is very much smaller than the ilium. It is 

 generally in the shape of a thin elongated plate of bone more or 

 less expanded dorso-ventrally towards the hinder end, where it 

 generally anchyloses with the distal portion of the postacetabular 

 part of the ilium, thus enclosing a vacant space between it and 

 the ilium — the ilio-ischiatic foramen. In some Birds — as the 

 Ostrich, Cassowary, Tinamou, Apteryx, and a few others — the 

 ischium does not anchylose distally with the ilium, so that there 

 is a deep notch, instead of a foramen, between these bones, as 

 is the case in ourselves. 



In the Ehea alone the ischia anchylose together beneath the 

 caudal vertebrae, forming an iscJiiatic symphysis. The ischium 

 develops from its inferior margin a small ventral process, which is 

 situated a little behind the acetabulum. This process may 

 anchylose with the pubis. 



The pubis is a long narrow bone which forms the antero- 

 inferior part of the acetabulum, and thence runs backwards 

 near the inferior margin of the ischium, which it may or may 

 not exceed in extent. The distal end may be more or less ex- 

 panded, but in the Ostrich alone does it unite with its fellow of 

 the opposite side to form a, pubic symphysis. It may anchylose 

 extensively with the ischium, or a long notch — the obturator 

 notch — may be left between them. It may anchylose with the 

 ischium towards the distal end only, so converting the notch 

 into an obturator foramen ■ or it may anchylose with the ischium 

 both towards its distal end and also with the " ventral process " 

 of the ischium, remaining elsewhere separate, and so forming 

 two obturator foramina. Often a more or less marked process 

 projects forwards from the pubis from beneath the acetabulum. 

 This is called sometimes the ilio-pectineal process, and some- 

 times the prepubis. 



In a general way we may consider the ischium to repeat in 

 the lower limb the coracoid of the thoracic girdle, and the 

 pubis to represent the clavicle; but this parallelism is not 

 exact. 



The slceleton of the leg consists of a single bone, called the 

 " femur," in the thigh ; of two bones named respectively the 

 " tibia" and the " iibula" in the leg or " cms " ; of one or two 

 bones in that part called in Ornithology the " tarsus '' ; and of 

 the bones of the foot. These latter answer to the bones of our 



