302 PEOr. W. K. PAEKEE ON .EGITHOGNATHOUS BIEDS. 



The bone itself (fig. 4, v) is concave above ; it was formed from two symmetrical 

 scythe-shaped moieties, each of which began as endostoses in the corresponding " vome- 

 rine cartilage :" they ossified it thoroughly, and then seized upon each alinasal wall, 

 where they ended by turning inwards. But the broad cartilaginous band below (see 

 fig. 4, i. a. I) has a separate bony graft, the " septo-maxillary " (fig. 6, s.mx); and this, 

 with the extended bony matter in the nasal cartilages, gives the peculiar appearance 

 the vomer of the adult bird has when viewed from below (fig. 6) : it resembles the face 

 of a bull, the ascending laminte being little ears, and the outturned septo-maxillaries 

 its short diverging horns. The septum nasi ossifies in the adult : — in front, from the 

 ossification of part of the alse ; and the freed trabecular part (tr) by its own centre. 



The compound " vomer " of the adult Crow has therefore been formed from : — • 



a. A pair of vomerine cartilages. 



b. A pair of vomerine centres (endostoses of those cartilages). 



c. A pair of septo-maxillaries — exostoses formed upon the following, namely 



d. The end of each inturned alinasal wall, combined with the end also of its 



" outgrowth " the " alinasal turbinal." 



Then, as if this amount of metamorphosis were insufficient, the crura of the vomer 

 coalesce with the ethmoid processes of the palatines (e.jm), so that in each movement 

 of the face the whole nasal labyrinth is carried forwards and backwards by the mobile 

 pterygo-palatine arch. This second preeoral arch has a short and stout suspensory seg- 

 ment, the " pterygoid " (pg), which, however, as the bird grows older, becomes slenderer, 

 especially behind, where it acquires the epipterygoid hook or " hamular process." It 

 flattens out horizontally in front, and then sends a spur to overlap the palatine. This 

 becomes the " mesopterygoid " — separate in a young flyer (fig. 5, mspg), but soon to 

 ankylose with the palatine. 



The distal segment of this arch, the palatine [pa) is greatly longer than the pterygoid : 

 with the fore end of the latter it tends to form a commissure, which is only completed 

 by membrane ; it is then bowed out on each side, and each moiety runs far forwards as 

 a finely pointed style (fig. 1). Where it is overlapped by the pterygoid, there it is split 

 mesiad into two laminse; these end in front in sharp spurs, to the upper of which the 

 vomerine legs are articulated ; the lower or " interpalatine processes " are merely united 

 by a ligament to the maxillo-palatine spatulse. 



If this were all, the palatines of the Crow would correspond with those of the Hemi- 

 pod. But the first bony shaft does not calcify all the arch-moiety ; it leaves an external 

 outgrowth, which has time to become solid hyaline cartilage: this is the "transpala- 

 tine " element {t.pa), and it is a sure sign and correlate of complete segithognathism. 

 This free auricle of cartilage becomes, in a young summer-bird, a distinct bone (fig. 5, 

 t.pa), ossifying at first by endostosis ; and then, in the adult, it shows no sign of having 

 ever been separate from the body of the palatine (fig. 6, i.pa, t.pa). 



