SKELETON. 



97 



atum,' a small bone connecting the lacrimal with the palatine or jugal bar. All 



of the bones enumerated on page 71 may appear in the development of the lower 



jaw. 



Teeth occur only in a few fossil birds, where they are implanted in sockets; 



several species are known to have a dental ridge in the embryo (see Development 



of Teeth). The hyoid apparatus (fig. 101) 

 consists of a pair of cornua (first branchials) 

 sometimes extremely long, connected by the 

 hyoid copula (os entoglossum), behind which 

 is a second copula (urohyal) while in front of 

 the entoglossum is a 'paraglossaP element 

 with a pair of small cornua. 



The palatal structures have considerable 



^^^ importance in classification. All living birds 



can be arranged in two groups. In the *dro- 

 maeognathous' group the palatines and ptery- 



i 



FIG. too. Ventral view of skull 

 of a duck; letters as in fig. 68. 



FIG. 101. Hyoid of hen, after Parker. 

 e, entoglossal; p, paraglossal; u, urohyal; 

 ///, posterior cornua. 



goids do not articulate with the rostrum, the vomers usually intervening. In 

 the 'euornithes' the articulation occurs. The latter are subdivided into the 

 desmognathous forms where the vomer is small or wanting, and the maxillo- 

 palatines meet in the middle line; the schizognathous in which the maxillo- 

 palatines do not meet the vomer or each other; the aegithognathous, like the 

 last except that the vomer is broad and truncate; and the saurognathous 

 with^delicate, rod-like vomers and maxillopalatines scarcely extending inwards 

 from the maxillaries. 

 7 



