AND DEVELOPMENT OF THE BIRD'S SKULL. 117 



The forth-drawing (prognathism) of the facial bars has been carried to its uttermost 

 extent in the Humming-bird ; but the secondary parts of the trabecular arch occupy two 

 thirds of the length anteriorly, their endoskeletal axis or prenasal rostrum early under- 

 going absorption. Behind, the apices of this arch are buried and lost in the outworks 

 of the tympanic cavity ; and below, just in front of this part, the great splint, the para- 

 sphenoid, marks the bowed converging bars (Plate XXII. figs. 2, 3, 4, 8, pas). Here, just 

 outside the common Eustachian meatus (eu), the trabecule have sent out conjuga- 

 tional spurs, with their obliquely fore-looking facets for the pterygoids. 



This high form gives us the extreme of a series commenced in the Struthionidse, where 

 the hinder end of the pterygoid is wedged in in the Emu between the quadrate and 

 basipterygoid process. Even in some " PatitsB " (see " Ostrich Skull," plates vii.-xiv.) 

 the articulation is further forwards, whilst the series is obtained by passing to the 

 Tinamou (plate xv.), the Syrrhaptes (Trans. Zool. Soc. 1863, vol. v. pi. xxxvi. fig. 1); 

 then come the Plovers, Pigeons, Owls, &c, where it is in the middle ; the " Alectoro- 

 morphae " and " Chenomorphae," where it is at the anterior third ; and, lastly, here in the 

 " Trochilidse " it is quite at the fore end. Of necessity, this relative motion, as it were 

 of the palatine on the trabecular arch is attended with shortening of the basipterygoid 

 processes as we pass along the series from the Emu to the Humming-bird. The tra- 

 becular base of the meso-ethmoid (Plate XXII. fig. 3, pas) is short, broad, pointed, and 

 keeled in front ; and the hinge between this part and the septum nasi is finished by 

 uncleft cartilage above (Plate XXII. fig. 4, eth, sn). The remainder of the trabecular bar 

 is one with a most small true nasal septum ; there is a larger posterior and a smaller 

 anterior osseous centre in this small cartilaginous keel (fig. 4, sn). There are several 

 secondary bones applied to the trabecular arch besides the hinder plate, or parasphenoid. 

 In front the premaxillaries (px) take the lead; they are here at their highest develop- 

 ment ; they reign in this type, especially, and all things else in the organism are in con- 

 formity with them. 



In the old bird (fig. 2) the premaxillaries are three fourths the length of the face ; in 

 the nestling (fig. 8) they are only two thirds ; so that it is evident that this excessive 

 prognathism takes place by the working of a general morphological law. 



The boundaries of this double bone are best seen in the young (fig. 8) ; the dentary 

 processes (clpx) nearly reach the maxillo-palatines (mxp) behind, and the palatine pro- 

 cesses (figs. 8 & 9, ppx) are the twentieth of an inch shorter ; as usual, the nasal pro- 

 cesses (fig. 5, npx) are strongly grafted on and ankylosed to the forehead. Laterally 

 the upper and lower portions of the premaxillaries are thinned out extremely, and present 

 ragged edges towards each other : this can be seen in the lower view (fig. 2). The halves 

 of the vomer are thoroughly fused together in my young specimen (figs. 8 & 9) ; they show 

 no sign of being formed on any thing else than a tract of fibrous tissue, and their likeness 

 and dissimilarity to the true Passerine vomer is well shown. 



The long anterior spike in which the coalesced pieces terminate in front would not of 

 itself exclude them from the " iEgithognathse ;" in the typical Chough (Fregihis graculus), 

 and in the aberrant Lyre-bird (Menura superba), the double vomer is blunt-pointed in 

 front ; but in them, supero-laterally, the scars are seen in the dry skull where the alinasal 



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