INTRODUCTION. IX 



movcably aiicliyloseJ, as are the lumbar and sacral verte- 

 bra3. The caudal vertebrae are moveable, and the last ver- 

 tebra is m the form of a compressed disk, to support the 

 tail; and this bone sometimes differs in form, according to 

 the sex, as in the Pea-fowl. 



The pelvis is much extended longitudinally, and is also 

 ancliylosed with the vertebral column, and thus affords a 

 large surface for tlie attachment of the muscles which 

 support the trunk upon the thighs. The iliac bones are 

 long, and excavated internally to receive the kidneys. 

 The ischia and the pubic bones are widened in their 

 span, for the development and expulsion of the eggs, and 

 the latter bones are not joined together. 



The sternum, to wliich are attached the povv^erful mus- 

 cles that move the wings, is of great extent, in general co- 

 vering not only the thoracic but the abdominal cavity. Its 

 extent too is increased by a central ridge or crest, or keel, 

 Avhich is of greater or less depth, according to the powers 

 of flight. The posterior surface originally formed of two 

 forked lateral processes, varies greatly according to the 

 greater or less ossification of the notches between these 

 processes. In some, the spaces are entirely filled up, or 

 only occupied by one or two foramina, as in most diurnal 

 birds of prey. Swifts, Humming-birds, Parrots, l^etrels, 

 &c., and in these birds the power of flight is at its 

 maximum. In others the notches remain, and are of greater 

 or less extent both in length and width according to the 

 tribes. The ribs are joined to the sternum by bone, instead 

 of by cartilage, to increase the strength of the cliest ; 

 and to each rib a small appendage or bone is solidly 

 attached, directed upwards and backwards over the suc- 

 ceeding rib, thus concurring to give additional solidity 

 and stren2;th. 



O 7 



