Ari'KNDix. :M[> 



another by a septum (tij>-. Vlll. 1). Tlic bones olthe palate (lig. IV. 2) 

 present four distinct types of structure, whicli are of considerable 

 importance for iiurposes of classification. The ditfeiences between the 

 four types may be studied in the recess No. 4^ of the Central Hall and 

 in the window-case illustrating the classification of the Carinatce. The 

 lower jaw is suspended from the skull by means of a movable bouc known 

 as the quadrate (fig. V. 2). The two halves of the lower jaw (fig. A . 3) 

 are united in front, forming a symphysis, and are covered with a bony 

 sheath in front, like the upper jaw. 



In the vertebral column four divisions may be distinguished, viz. 

 the cervical, thoracic, synsacral, and caudal. (]) The cervical or lu'ck 

 division (fig. V. ."») possesses an extraordinary degree of fiexibility, 

 which is necessary owing to the anterior limbs having become exciusively 

 organs of locomotion, and most of the complicated movements executed 

 by those limbs in Alammals and Reptiles have to Ije performed in J5irds 

 by the bill. The uumljcr of vertebr;c of this division varies from eight 

 to twenty-three. (2) In many birds the thoracic vertebne (fig. V. G) are 

 fused aud form a solid bar of bone. This condition is not necessarily con- 

 nected with strong powers of flight, for though found in all Falcons it does 

 not occur in Eagles, in which the vcrtebr;e arc free. (3) Thesynsacrum 

 (fig. V. 7) is a long bone, generally formed of the last thoracic vertebra 

 and the united lumbar, sacral, and anterior caudal vertebne, to which the 

 iliac bon(>s are immovably attached. Although only two of the segments 

 of this series of fused vertebne can be regarded as true sacrals, the whole 

 series is sometimes described as the sacrum and varies in number from 

 I'leven to twenty. (4) Of free or movable caudal vertebne (fig. \'. 8 ) 

 there are eight or ten, the last being remarkable for its size, shape, and 

 function. From its shape it has been called the ploughshare- bone 

 {pi/(/osti/le). An examination of very young birds shows that in early 

 life it is composed ot ii'om four to ten free vertebne which become 

 completely fused together in the adult, and form the single bone which 

 supports the tail-feathers aud to which strong muscles are attached. 

 Thus, although the tail of a typical adult bird is apparently reduced to 

 a short series of a few segments well adapted for the e.xecutiou of 

 powerful movements, embryology shows that originally this portion of 

 the vertebral column is very much longer. For instance, in the young 

 Swan it consists of not less than twenty-seven vertebras, a condition which 

 considerably lessens the apparently great difiereuce between the tail ot 

 an adult Swan and that of a Reptile or Archceoptenjx. 



All the thoracic and some of the posterior cervical vertebrae bear 

 movable ribs (fig. V. 9), their conueetioa with tlie sternum being effected 

 by means of short sternal ribs (fig. V. 10). In order to strengthen the 

 thorax, the ribs are connected with one another by bony spurs known 



