196 ELEMENTS OF ORNITHOLOGY. 
The tschium 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 tow ards 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 
isa deep notch, instead of a foramen, between these bones, as 
is the case in ourselves. 
In the Rhea alone the ischia anchylose together beneath the 
caudal vertebrae, forming an ischiatic symphysis. The ischium 
develops from its inferior mar gin 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 forw ards from the pubis from beneath the acetabulum. 
This is called sometimes the 7/io-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 skeleton of the leg consists of a single bone, called the 
“ femur,’ in the thigh; of two bones named respectively the 
“tibia” and the “fibula” in the leg or “‘crus”; 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 
