OSSEOUS SYSTEM OF AVES. 



51 



29 



iienceplialic prolongations of the neural axis), and in some birds 

 expanding above, and appearing, as in Batrachia, on the exterior 

 of the cranium, as between ii and 15, in fig. 29, and at 14, fig. 31. 

 The confluent prefrontals, fig. 28, u, support the fore part of the 

 frontals, 11, and a greater proportion of the nasals, 15; they are 

 in most birds raised far above the (hypa- 

 pophysial) ossification of the lower cor- 

 tical part of their centrum, called the 

 ' vomer,' fig. 32, 13, the large eyeballs, 

 and their thin but deep interorbital sep- 

 tum, being interposed ; this septum is 

 ossified in different degrees in different 

 birds. The typical position of the pre- 

 frontals is retained in Aj)teryx and Di- 

 nornis. The condition of the prefrontals 

 in some fishes (^Xiphias)^ will aid the 

 comprehension of the developement of 

 the prefrontals between the orbits in 

 these ivingless birds. The frontals are 

 large, triangular (fig. 29, 11), or sub- 

 rhomboid, plates. The post-frontal ap- 

 pears as a distinct bone in some birds 

 (Emeu)^ fig. 31, 12; it varies much in 

 length ; it bends down, and is the longest 

 of the three cranial diapophyses in the 

 Eagles ; it curves forward, meets, and 

 coalesces, w^ith a backward production of 

 the lacrymal in some Parrots, fig. 30, g. 



The nasal bones rarely unite Avith each other in any proportion, 

 fig. 29, 15 ; in most birds they are separated by the union of the 

 nasal process of the premaxillary, 22', 

 with the frontal or prefrontal : save in 

 the Emeu, fig. 31, 15,^ and some other 

 Struthionidce, the nasal bifurcates ante- 

 riorly to form the hind boundary of the 

 nostril, and the hinder prong descends 

 to join the maxillary, dividing the 

 nostril from the antorbital vacuity. 



The premaxillary, figs. 28 32, 22, 

 upon which the upper mandible is moulded, follows, in a minor 

 degree, aU the varieties of that much diversified part in Birds : it 



Skull of young Ostrich. 



Skull of Parrot. 



' CXL-. p. 52, pi. 1, fig. 5. U. 2 XV1IT-. vol. iii. pi. 39, figs. 1 and L>, li\ 



=* xviir. vol. iii. pi. 39, 14. 



E 2 



