362 



ZOOLOGY 



SECT. 



The premaxillae (p.mx., PMX.) are united into a large triradiate 

 bone which forms practically the whole of the upper beak. The 

 maxillae (mx., MX.}, on the other hand, are small, and have their 

 anterior ends produced inwards into spongy maxillo-palatine pro- 

 cesses (Fig. 971, mx.p., Fig. 972, mx.pcd.pr.). The slender posterior 

 end of the maxilla is continued backwards by an equally slender 

 jugal (fu., JU.) and quadrato-jugal (QU. JU.), to the quadrate. 

 The latter (qu., QU.) is a stout three-rayed bone articulating by two 

 facets on its otic process (ot. pr.) with the roof of the tympanic 

 cavity, sending off an orbital process (orb. pr.) from its anterior mar- 

 gin, and presenting below a condyle for articulation with the man- 

 dible ; it is freely moveable upon its tympanic articulation, so that 

 the lower jaw has a double joint as in Lizards and Snakes. 



The palatines (pi., PAL.) have their slender anterior ends anky- 

 losed with the maxilla, their scroll-like posterior ends articulating 

 with the pterygoids and the rostrum. The pterygoids (pt., PTG). 

 are rod-shaped and set obliquely : each articulates behind with the 

 quadrate, and, at about the middle of its length, with the basi- 



ptery-goid process, a small facetted 

 . projection of the base of the 

 rostrum. There is no vomer. 



The mandible of the young Bird 

 consists of a cartilage bone, the 

 articular (ar., ART.), and four mem- 

 brane bones, the angular (an., ANG-.), 



b.br.z 



s.st.. 



st 



e.st. 



cbr 



L^ 



FIG. 974. Columba livia. The columella auris 

 (magnified). The cartilaginous parts are dotted. 

 e. st. extra-stapedial ; i. st. infra-stapedial ; s. st. 

 supra-stapedial ; st. stapes. (From Parker's 

 efj.br Zootomy.) 



supra-angular (s.an., S.A NG.), dentary 

 (d., DNT.), and splenial (SPL.\ all 

 having the same general relations as 

 in the Lizard. The hyoid apparatus 

 (Fig. 973), is of characteristic form, 

 having an arrow-shaped body (b. hy.) 

 with a short pair of anterior cornua 

 (c. hy.) derived from the hyoid arch, and a long pair of posterior 

 cornua (c.br., ep.br.) from the first branchial. The columella 

 (Fig. 974) is a rod-shaped bone ankylosed to the stapes, and bear- 

 ing at its outer end a three-rayed cartilage or extra-columella 

 (e.st., i.st., s.st.) fixed to the tympanic membrane. 



The shoulder- girdle (Fig. 968) is quit'e unlike that of other 



FIG. 973. Columba livia. Hyoid 

 apparatus. The cartilaginous parts 

 are dotted. 6. br.l, basi-branchials ; 

 b.hy. basi-hyal; c.br. cerato-branchial; 



c. hy. hyoid cornu ; ep. br. epi- 

 " 'il. 



branchial 



