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. ror) 
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 ‘paraglossal’ 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- 
mzognathous’ group the palatines and ptery- 
Fic. roo.—Ventral view of skull Fic. 1o1.—Hyoid of hen, after Parker. 
of a duck; letters‘as in fig. 68. e, entoglossal; ~, paraglossal; u, urohyal; 
III, 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 miiddle line; the schizognathous in which the maxillo- 
palatines do not meet the vomer or each other; the egithognathous, like the 
last except that the vomer is broad and truncate; and the saurognathous 
with delicate, rod-like vomers and mazxillopalatines scarcely extending inwards 
from the mazxillaries. 
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