THYNG: SQUAMOSAL BONE. 
415 
ogous with those of the Rhynchocephalia and Crocodilia. Further, 
almost all authors are agreed in saying that of the three temporal 
elements (supratemporal, squamosal, quadratojugal) of the primitive 
reptiles (Cotylosauria) the middle one has disappeared, only the 
medial and the lateral ones persisting. 
In this I believe them to be in error. If it be the supratemporal 
that has disappeared in the Rhynchocephalia and Crocodilia, as I 
have attempted to prove, we should hardly expect it to reappear in the 
Dinosaurs, an order which is usually regarded as having had these 
for its ancestors. In many of the Dinosaurs the upper of the two 
temporal bones extends beyond the otic capsule sufficiently to cover 
the head of the quadrate. In others (Anchisaurus, fig. S) it extends 
for some distance down beside the quadrate and in a few (Cerato- 
saurus, Baur, ’91, p. 446; Ceratops, Marsh, ’96, p. 210) we find that 
it actually enlarges so as to articulate with the quadratojugal. 
From this evidence of its relation to the otic capsule, quadrate, 
quadratojugal, and its articulation with the postorbital, and the 
ancestral history of the group, I prefer, until more proof to the contrary 
is advanced, to regard the upper of the two elements as the squamosal. 
Theriodontia, Anomodontia, and Sauropterygia .— It now remains 
to return to the Cotylosauria and to follow out that line of reptiles, 
the so called Theromorpha, which many claim has given rise to the 
Mammalia, but which will be considered here as a side branch that 
early became extinct. Besides the so called mammalian characteris¬ 
tics (to be explained by parallel development), the Theriodontia are 
generally recognized as intermediate between the Cotylosauria on the 
one hand and the Anomodontia and Sauropterygia on the other. 
The investing bones of the temporal region of the Theriodonts 
(fig. T) form a broad arcade which bounds the supratemporal vacuity 
externally and below. This arcade is composed of a jugal (/.) and a 
second bone ( Sq .), almost universally regarded as the squamosal. It 
covers the external surface of the quadrate nearly or quite to its artic¬ 
ular end, extends upon the otic capsule, and connects with the parietal 
by a narrow process. 
In the temporal region of the Anomodontia and the Sauropterygia 
we find practically the same condition as in the Theriodontia. A 
large bone covers the external surface of the quadrate, even entering 
into articulation with the articular, and extending dorsally to join 
the parietal. In front, it articulates with either the postorbital or the 
