6o2 



BIRDS. 



region. The complex sacral region consists of the last 

 thoracic (with ribs), two or three lunibars, three or four 

 sacrals, and six caudals all fused. Lastly, there are about 

 six free caudals, ending in a pygostyle or ploughshare bone, 

 which represents a fusion of several vertebrae. 



When we examine one of the cervical vertebrae, we notice 

 that the anterior surface of the centrum has a complex and 

 distinctive curvature, often described as saddle-shaped. It 

 is concave from side to side, convex from above downwards. 

 Posteriorly the curvatures are, of course, the reverse. The 

 vertebra also bears expanded transverse processes, perforated 

 on each side by an aperture for the vertebral artery, anterior 

 articular processes or zygapophyses, posterior articular pro- 



50 ^^^ 



S.Oc 



^£.0c. 



Fig. 2c 



-Disarticulation of Bird's Skull. 

 Membrane bones shaded. 



(After Gadow.) 



B. Oc, basi-occipital ; E. Oc, ex-occipital; S. Oc, supra- 

 occipital; Pa.^ parietal ; Fr., frontal ; Xa., nasal ; /;//., premaxilia ; 

 ^/., maxilla ; /;(., jugal ; Qj.^ quadrato-jugal ; Qu., quadrate ; />c., 

 periotic ; Sq., squamosal ; BS.^ basi-sphetioid ; OS., orbito-sphenoid ; 

 /'?-.vS'//i., pre-sphenoid ; 7'^., vomer; 20s., interorbltal septum; £■-, 

 ethmoid; Se., nasal septum; Dc, dentarj-- ; 5"/., splenial ; An., 

 angular; Sa., surangular ; A?-., articular; J/ A'., Meckel's 

 cartilage. 



cesses, and a large )ieural arch culminating in a neural 

 spine. 



The ribs, borne by five vertebra;, have two heads— a 

 capitulum articulating 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. On the posterior surface of each of the first 



