ANNALS 
MEDEDELINGEN 
OF THE VAN HET 
Transvaal 'Museum. 
VOL. III. JULY, 1911. No. 2. 
NOTE ON THE RELATIONSHIP OF THE MAXILLA OF VIPERS 
TO THAT OF COLUBRIDAE.. 
By John Hewitt, B.A. (Cantab.). 
The features of the maxillary bone and its dentition afford the only known 
method of distinguishing the Viperidae from the Colubridae, and of 
subdividing the latter family into the three series, Aglypha, Opisthoglypha, 
and Proteroglypha. In the British Museum Catalogue of Snakes, Mr. 
Boulenger expressed the opinion that the maxillary bone of the viper is to 
be derived from the opisthoglyphous type, a view which was accepted and 
repeated by Dr. Gadow in the “ Cambridge Natural History ”, though the 
necessary evidence is not stated by either authority. It may be presumed 
that according to this view the opisthoglyph maxilla has given rise to the 
viperine type by an upward tilting of its anterior portion through an angle 
of ninety degrees, the poison fangs being situated at the fulcrum, this 
change of position being accompanied by the loss of all the solid teeth. 
As an alternative to the tilting hypothesis it is conceivable that the whole 
of the anterior portion of the maxilla has aborted, and subsequently the 
fang-bearing portion has expanded vertically upwards into a cylinder. 
After careful examination of a series of skulls it appears to me more 
probable that the Viperidae are not of opisthoglyphous ancestry, but are 
more closely related to the proteroglyphous stock, as was believed by the 
earlier morphologists. A typical viper such as the puff-adder (. Bitis 
arietans ) shows a very considerable degree of modification in its skull 
characters, if we suppose it to be derived from a colubrid type, but there 
are other vipers, such as the night-adder ( Causus rhomb eatus) and 
Atractaspis, which furnish connecting links between the two families. 
In those familiar types which have been so often figured, Bitis, Vipera, 
Crotalus, the maxilla is a short sub-cylindrical bar, vertically arranged, 
inferiorly bearing the large poison glands, but no solid teeth, and attached 
above by a definite movable joint to the anterior surface of the prefrontal 
bone ; in the Colubridae the prefrontal bone ordinarily forms a transvers e 
partition stretching from the maxilla towards its fellow in the middorsal lin e 
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