BIRDS. 



p mx 



ploughshare bone, a fusion of about four vertebrae (cf. 



coccyx in man). This bone serves as a base for the 



rectrices. 



A cervical vertebra 

 shows on the anterior 

 surface of the centrum 

 a distinctive curvature, 

 described as saddle- 

 shaped or heteroccelous. 

 It is concave from side 

 to side, convex from 

 above downwards. Pos- 

 teriorly the curvatures 

 are, of course, the re- 

 verse. 



The ribs have two 

 heads a capitulum arti- 

 culating with a centrum, 

 a tubercle articulating 

 with a transverse process. 

 The ventral part of the 

 rib, which reaches the 

 sternum, is called the 

 sternal rib, and is joined 

 at an angle to the dorsal 

 part, which articulates 

 with a vertebra. In 

 Birds the sternal ribs 

 are always bony ; in 

 Mammals they are usu- 

 ally cartilaginous. On 

 the posterior surface of 



FIG. 3 i4.-Under surface of gull's skull. ch f the first ^ four 

 From Edinburgh Museum of Science thoracic ribs there IS an 



and Art. uncinate process, absent 



c ., Condyie; b.t., basitemporai ; b.s. basi- O nly in the S. American 



sphenoidal rostrum; pt., pterygoid, pa., , T . 



palatine; v., vomer ; p.m.r., premaxilla ; SCreamerS (ralamedeae). 

 m.r., maxilla; /., jugal ; q.j., quadrato- HTU p S V U 11 V, as n 



jusal; q. t quadrate. 



rounded cranial cavity, 



large orbits, and a narrow beak, which is mostly composed 

 of the premaxillce. All the bones are fixed except the 



c 



