PHYLUM CHORDATA 



467 



b.bn-t 



by ligament ; its anterior edge bears a pair of deep grooves 



for the articulation of the coracoids. 



The skull (Fig. 279) is distinguished at once by its 



rounded brain-case, immense orbits, and long pointed beak. 



The foramen magnum (/. m) looks downwards as well as 



backwards, so as to be visible in a ventral view, and on its 



anterior margin is a single, small, rounded, occipital condyle 



(o. c). Most of the bones, both of the cranial and facial 



regions, are firmly ankylosed in the adult, and can be made 



out only in the young bird. 



The premaxillae (Fig. 279,/. mx) are united into a large 



triradiate bone which forms 



practically the whole of the 



upper beak. The maxilla; 



(Fig. 279, mx), on the other 



hand, are small, and have 



their anterior ends produced 



inwards into spongy maxillo- 



palatine processes (Fig. 279, 



mx.p). The slender poste- 

 rior end of the maxilla is 



continued backwards by an 



equally slender jugal (jit) 



and quadrato - jugal to the 



quadrate. The latter (Fig. 



279, on) is a stout three- 

 rayed bone articulating by Fig. 280- Columbia livia. Hyoid ap- 

 paratus. The cart'laginous parts are 

 dotted, b br. I, basi-branchials; b ky, 

 basi-hyal; c br. cerato - branchial: 

 c. hy, hyoid cornu; ep. by, epi- 

 branchial. 



presenting below a condyle 



for articulation with the mandible : the mandible of the 

 young bird consists of a cartilage bone, the articular (Fig. 

 279, ar), and four membrane bones, which all coalesce in the 



i.br.z 



cp br 



two facets with the roof 

 of the tympanic cavity, and 



