64 ANATOMY OF VERTEBRATES. 



logons, in both Ovipara : but in the Bird the secondary peripheral 

 developments of the prefrontals are suppressed as in Batrachians 

 and some fishes (Xiphias),^ in which they form the anterior wall 

 of the orbit, occupying the anterior part of the interorbital space, 

 joining each other at the median line by an extensive vertical 

 cellular surface, and dividing the orbital from the rhinal cavities. 

 In the Apteri/x and Dinoi-nis the latter cavities are so developed 

 as to extend backward between the orbits to the cranium, the 

 front wall of which forms the back wall of the rhinal, instead of 

 the orbital, cavities. 



In most birds, however, the orbits intervene : tlie rhinal 

 chambers are small, and communicate with the upper and back 

 part of the nasal passages on each side of tlie prefrontal septum. 

 The passages are partly divided by bone developed from the 

 vomer. They usually extend obliquely backward from the outer 

 to the inner or palatal nostrils : but in the Toucans and Hornbills 

 the nasal passage descends vertically at the base of the huge bill. 

 The outer nostril is formed in front by the premaxillary, be- 

 hind by the nasal — each bone bifurcating to include the area, 

 into the lower part of the circumference of which the maxillary 

 usually enters. In the Rhea and Emeu, fig. 31, the outer bony 

 nostril is incomplete behind, the maxillary process or prong of 

 the nasal not being developed. In the Ostrich it does not reach 

 the maxillary. The external nostril is near the apex of the bill in 

 the Cassowary. In the Apteryx the external nostrils are minute 

 and subterminal ; but a linear groove extends back and widens 

 into a large triangular Aacuity, on each side the base of the 

 upper mandible in the skull. In the Petrels the nostrils are 

 pierced at the end of a tube upon the upper mandible. In the 

 PelecanidcB there is no outer nostril. The bony septum between 

 the nostrils is rarely entire. The nasal passage is continued 

 backward between the vomer and palatine, or betAveen the pre- 

 sphenoid and palatine, to open, usually by a single median fora- 

 men or fissure, or by a pair of such, divided, as in Dromaius, by 

 the vomer, fig. 32, 13, or, as in Struthio, by the vomer and pre- 

 sphenoid, upon the palate. 



Amongst the cranial peculiarities in Birds may be noticed the 

 bony style attached to the occiput in the Cormorant: the light 

 cellular bony core or support of the thick horn or horny crest, 

 in Casuarius galeatus ; which is expanded and flattened behind 

 in Casuarius Mooruk : the longer and narrower horn-core, re- 



' XVI-. p. 52, pi. 1, fig. .5, 14. 



