THE INTERNAL SKELETON, 173 
It does this by affording attachment to a bony girdle—called 
the “ pelvis ””—from which the lower limbs are suspended. 
The sacrum of a bird, being so extensive, includes more 
vertebree than does the pelvis of any beast or reptile, and we 
may distinguish three parts in it :— 
(1) A part made up of vertebree which may be taken to 
represent vertebra of the trunk, which have been absorbed by 
it. The vertebree which form this part may be called Jwmbo- 
sacral *, 
(2) A part which may be taken to be especially sacral, or the 
“sacrum” par excellence. Its vertebre are the true sacral 
ones. (Fig. 149, 8, 9, & 10.) 

VentTRAL Asprect oF SAcruM or YounG Ostricu. 
1-12, Centra ; d-d°, diapophyses of corresponding vertebra ; p'—p!, para- 
pophyses of corresponding vertebrx ; dp, conjoined dia- and para- 
pophyses of the vertebra marked 11. 
(3) A part made up of vertebrae which may be taken to 
represent vertebra of the tail, which have been absorbed into 
the sacrum. The vertebree of this region are termed wro-sacral. 
The number of vertebre thus anchylosed together varies 
from a dozen or eleven to thirteen, which is about the average, 
up to twenty. 
The whole sacrum is an elongated structure somewhat spindle- 
shaped, and is compressed between those bones of the pelvis 
* So called because these vertebre seem to answer to those vertebra of 
man and other mammals which are termed “lumbar,” and are the vertebrse 
which come between their dorsal vertebrm and their sacrum, 
