THYNG: SQUAMOSAL BONE. 
409 
while a third element, usually called the quadratojugal occurs lateral 
and ventral to this junction. It covers the external surface of the 
articular end of the quadrate, but Osawa (’96, pp. 449 and 520) calls 
it the tympanic. 
Comparisons of the skulls of Sauranodon, the Pelyeosauria, Palaeo- 
hatteria, Stenometopon, and Sphenodon can lead only to the conclu- 
Fig. P. — The posterior dorsal aspect of the left side of the skull in Sphenodon 
(Hatteria), after Rabl. F., frontal; Pa., parietal; Pf., postfrontal; Po., post¬ 
orbital; Sq., squamosal. 
sion that in the phylogenetic development of the last genus it is the 
medial (supratemporal) rather than the lateral (squamosal) of the 
two problematic elements that has been lost. The lateral in Saurano¬ 
don articulates with jugal, quadratojugal, postorbital, and quadrate, 
the medial with only the parietal and postorbital. The progressive 
enlargement of the supratemporal fossa must result in a corresponding 
decrease and final loss of the supratemporal, while the necessity of 
retaining strength in the cranial roof would cause a corresponding 
development of processes from either parietal or squamosal to meet 
the other element. The view that the lower or squamosal has dis¬ 
appeared involves numerous difficulties. While retaining its con¬ 
nection with the parietal, the supratemporal must at the same time 
gain connections with jugal, quadratojugal, postorbital, and quadrate 
almost exactly duplicating those of the last element, a case of substitu¬ 
tion rather difficult to imagine. 
