DEVELOPMENT OF THE SKULL IN THE OSTEICH TRIBE. 141 



lamina is, in the Ostrich, not extended backwards, in the Emu it does grow both back- 

 wards and upwards, and swells into a thick-lipped shell of bone (Plate XI. fig. 2, & 

 Plate XIII. fig. lS,pv.). This curious spongy shell is beautifully seen iii the Eagle, and 

 in many other birds : in some groups, for instance, all the " Lamellirostres," including 

 the Palamedeas, the bones meet and coalesce along the mid line — a curious anticipation 

 of the precisely similar junction of the maxillaries in all the Mammalia, and in the 

 Crocodiles. This prevomerine bridge is weU shown in Mr. Erxleben's figure of the 

 Balseniceps' skull (Zool. Trans, vol. iv. pi. 65, figs. 7 & 8, p. 297, there described by me 

 under the name of Turbinals, or " Ethmoidal pterapophyses"). 



The vomer (Plate XI. fig. 2, v.) in this embryo of the Emu is more than an inch in 

 length, nearly half the length of the whole skull and face ; as before mentioned, it is 

 extremely divergent behind, and like the Ostrich's vomer it is trifurcate in front ; the 

 middle prong is very long and slender. 



In this bone the Emu agrees with the Great Ostrich and not with the Rhea and 

 Cassowary, which have it bifurcate at both ends. The two ends of the Emu's vomer are 

 more nearly on the same plane than in the Rhea, where it comes nearer that of the 

 Chelonian ; in the next stage (six weeks old), at any rate in J). Novx HollandioB, the 

 vomer is straighter still. The long middle prong of the vomer in this early specimen 

 reaches to the very extremity of the septum ; but only the premaxillaries wrap them- 

 selves round the prevomerine rod — the approximated and coalesced "trabecular horns." 

 But typical birds teach that the whole base of the septum proper belongs to the inter- 

 maxillary apparatus. 



The bones that form the zygoma are very feeble, but they are all present in this and 

 in a few other birds. The first or true maxillary (Plate XI. fig. 1, & Plate XIII. figs. 

 12 & 13, mx.) is 5 lines long by | a line in thickness; it is pointed at both ends, and 

 lying close above, scarcely reaches as far backwards as the very prolonged angular pro- 

 cess of the intermaxillary. This last process, the zygomatic process of the prevomer, the 

 maxillary, and the zygomatic bone (jugal) [j.), are all tied together at one point external 

 to the junction of the palatine with the inner retral process of the vomer. The jugal is 

 twice the length of the quadrato-jugal {q.j-)-, which lies principally on the inside of the 

 zygoma, and they are each of them twice as thick as the maxillary. At this stage the 

 broadening of the whole palate has removed the maxillary and jugal one line from the 

 outer edge of the palatine even at its nearest part (Plate XI. fig. 2). 



The lingual cartilages (Plate XI. fig. 8) and the auditory columella (Plate XI. fig. 7) 

 are in much the same condition as in the Rhea at the full period ; only the columella 

 and the lower thyro-hyal are ossified, and that not perfectly. The basihyal has sent 

 backwards a uro-hyal {h.h., u.h.) process which is a step in advance of the Rhea, whilst 

 both these birds have the cerato-hyals alike in form and much more perfect than in 

 Stmthio (Plate XI. fig. 8, c.k). 



