OSTEOLOGY 139 



principal reason for the close association of these birds by 

 subsequent writers. In these birds (see fig. 77) the vomer is 

 broad posteriorly, and thrusts itself between the pterygoids 

 and palatines on the one side and the basisphenoid rostrum 

 on the other, and thus prevents their articulation. This is 

 the typical dromasognathous state ; but there are certain 

 modifications which will be described in detail later. The 

 ostrich, for example, is only dromaeognathous in that the 

 pterygoids and palatines do not articulate with the basi- 

 sphenoidal rostrum ; for the vomer in this bird is short and does 

 not reach back far enough to prevent (so to speak) the union. 



2. Desmognathism. — In a variety of birds belonging to 

 many orders the vomer has either disappeared or is very 

 small ; the two maxillo-palatine plates come into contact 

 in the middle line, as, indeed, they do in the dromaeognathous 

 skull. As with all the types of skull to be enumerated, the 

 pterygoids and palatines at the point of their union with 

 each other articulate with the basisphenoidal rostrum. (This 

 kind of skull is illustrated in fig. 78.) 



3.._ScMzognathistn. — This type is almost' as prevalent as 

 desmognathism. The vomer, well developed, terminates, as 

 a rule, in a point anteriorly. The maxillo-palatines, variable 

 in size and shape, do not meet across the middle line with 

 each other, or with the vomer. (See fig. 79.) 



4. ^githognathism. — Found typically in ' finches ' and 

 in passerines generally ; is very like the last type. The 

 distinguishing character (fig. 80) is that the vomer is 

 broad and truncated anteriorly, lying between the separate 

 maxillo-palatines. The skull is thus ' schizognathous ' 

 etymologically. To these four divisions Professor Paekee 

 has added — 



6. Saurognathism. — Exemplified in the woodpeckers. 

 The maxillo-palatines are extremely shght, hardly extending 

 inwards from the maxillae ; hence the skull is widely 

 schizognathous. The vomers are delicate paired rods. 



As stated in the foregoing brief epitome of the characters 

 of the several types of .skull, the facts seem to differentiate 

 the five types fully. Elliot Goubs remarks of desmo- 



