AND DEVELOPMENT OF THE BIRD'S SKULL. 109 



is of great interest, and is new to me. If any inorphologist knows what it answers to in 

 the lower vertebrate types it were well that he should explain it *. 



As the metamorphosis of these parts is very rapid, it is necessary to examine embryos 

 not more than a day or so in advance of or behind each other. In no longer a period, what 

 is displayed in fig. 1 is exchanged for what I have shown in fig. 3. Here the small osseo- 

 cartilaginous nuclei have developed into the large ox-faced vomer, with its broad anterior 

 part grafted on each side upon the alinasal wall, which turns directly inwards, and 

 spreads in a pedate form to apply itself to the vomer. On one side of the V-shaped 

 emargination the vomerine piece is fenestrate ; the bony matter here becomes detached, 

 and an additional bone formed. This additional bone is seen in the fledgling (see it in 

 the young Sparrow, fig. 4, smx). Not only does the vomer grow into the nasal wall, but 

 the alinasal turbinal (fig. 3, atb) also ; hence the huge size of the upper vomerine groove, 

 which is so striking in the Crow tribe (" Corvidge " proper) ; for the thick common end 

 of the wall and the turbinal approach the septum nasi, and, rising high on each side, 

 embrace the base of the septum. Another noteworthy characteristic of the Passerine 

 face is the elbowed form of the palatines near their hinder third ; this out-bent part does 

 not ossify " by first intention," but lingers until it is solid hyaline cartilage, and then 

 receives its own endosteal centre. This new bone is an arrested " transverse " element, 

 my " transpalatine " (tpa). 



That part of the Passerine palatine which is arrested from forming a bony palatal floor 

 generally exists as a free fore-looking spine. This is well seen in the Sparrow (fig. 4, 

 ipa) ; it is the " interpalatine process." In Ducks and Swans this is a separate knuckle 

 of bone ; and in looking over a large number of Starlings' skulls, I find it in certain of 

 them (see Plate XX. fig. 12, ipa). 



Other parts of the Passerine face must be noticed.; but I turn now to the most striking 

 condition of the vomer I have hitherto found in the group : it is seen in the native 

 Wren [Troglodytes vulgaris). When the whole palate of the bird is viewed (Plate XXI. 

 fig. 5, v), the vomer is seen to be as large, relatively, as in the " Ratitas ;" but its 

 anterior third is composed of true cartilage. In a spirit-specimen, by careful dissection, 

 I have been able to make out what is shown in fig. 6 on a larger scale. Here one of the 

 palatines (pa) and both of the maxillo-palatine hooks are removed; they are, however, 

 indicated by a dotted outline. 



* Finding the development of the Passerine "vomer" so totally unlike what I always supposed, namely, that it is 

 an endosteal ossification of cartilage, my mind cast about for some symmorph in the cold-blooded types and in the 

 Reptilian birds (Ratitse). I had not far to seek ; for lying unexplained in my memory were certain structures in the 

 Snakes and also in the struthious Shea, which I had figured years ago (Phil. Trans. 1866, plate x. fig. 14, the alate 

 cartilages above v), but which had hitherto resisted all efforts at explanation. On reexamination of these parts in the 

 Mlua chick, I find that they are free cartilages in the maxillo-palatine region, and attached to those processes and to 

 the fore forks of the double vomer by fibrous tissue. In the Snake the nasal glands and their bony capsules, the 

 vomers and septo-maxillaries (P), are flanked on their outside by an arcuato-spatulate flap of cartilage, continuous 

 by a narrow stalk with the recurrent laminae, or separate from that process, both states occurring in the same skull. 

 As in the furculum of the same bird (Linota, see " Shoulder-girdle and Sternum," plate xv. figs. 12-15), the Linnet's 

 " vomer " is a morphological compound, and the counterparts of its component elements are persistently separate in 

 the cold-blooded types. 



Q2 



