XIII 



PHYLUM CHORDATA 



399 



The skull of Birds is generally remarkable for its huge orbits 

 separated by a thin interorbital septum, and for the comparatively 

 small size of the ethmoid bone and its turbinals. The most 

 striking exception is afforded by the Kiwi (Apteryx) in which the 

 orbits (Fig. 1003) are small and indistinct, while the olfactory 

 chambers (Ec. Mh) extend backwards between the eyes ; the orbits 

 being therefore separated from one another by the whole width of 

 the organ of smell. The same thing occurs, to a less degree, in 

 the Moas. 



In its essential features the skull is remarkably uniform 

 throughout the class. The rounded form of the brain-case, more 

 or less concealed externally by ridges for the attachment of 

 muscles : the upper beak composed mainly of a great triradiate 



Wv.2T.Jn.ZV 



Nv.V 

 I AlSph 



FIG. 1003. Apteryx mantelli. Skull of a young specimen, side view. The cartilaginous 

 parts are dotted. Al.sph. alisphenoid ; ang. angular; en. 1, en. 2, condyle of quadrate; !> ,>f. 

 dentary ; d./n:, d. fir. descending processes of nasal and frontal ; Ec.Eth. ecto-ethmoid ; Ex. Col. 

 extra-columella ; Ex. oc. ex-occipital ; Ju. jugal ; Luc. lacrymal ; lac. for. lacrymal foramen ; 

 Na. nasal; na. up. nasal aperture ; Sr. II, III, IV. optic foramen, transmitting also the 3rd 

 and 4th nerves ; Nc. V, foramen for orbito-nasal nerve ; Nv. VII. for facial ; Pa. parietal ; 

 Pal. palatine; pa. oc. pr. par-occipital process; Pmx. pre-maxilla ; Pr. ot. pro-otic; Qv. Jv. 

 quadrato-jugal ; Qu. (orb. pr.) orbital process of quadrate ; 5. orb. F. supra-orbital foramen ; 

 &1. squamosal. (After T. J. Parker.) 



premaxilla ; the single, small, rounded occipital condyle ; the 

 slender maxillo-jugal arch ; the large parasphenoidal rostrum ; 

 the freely articulated quadrate, with its otic, orbital, and articular 

 processes ; the absence of the reptilian post-frontals ; and the early 

 ankylosis of the bones ; all these characters are universal among 

 Birds. There are, however, endless differences in detail, some of 

 which, connected with the bones of the palate, are of importance 

 in classification. 



In the Ratitse and the Tinamus (Crypturi) there are large 

 basi-pterygoid processes (Fig. 1004, B.ptg.pr) springing, as in 

 Lizards, from the basi-sphenoid, and articulating with the ptery- 

 goids near their posterior ends. The vomer ( Vo) is large and 

 broad, and is usually connected posteriorly with the palatines (Pal} 

 which do not articulate with the rostrum. The maxillo-palatine 



