THYNG: SQUAMOSAL BONE. 
401 
Cotylosauria .— In the skull of the Cotylosauria (Cope, ’80, p. 304, 
Pareiasauria; Seeley, ’89) the most primitive of known reptiles there 
is practically the same arrangement of the elements in the temporal 
region as is found in the Stegocephala. There is here a complete 
bony roof consisting as there of supratemporal (fig. E, St.), squamosal 
(Sq.), and quadratojugal ( Qj .), the homologies of these elements being 
complete. In Procolophon (fig. F), according to most authors, there 
is an exception to all other Cotylosauria in that there is a small vacuity 
in the bony roof between the postorbital ( Po .), squamosal (Sq.), and 
jugal bones (J.) but in a letter quoted by Williston (: 04, p. 181) 
Broom apparently denies the existence of the gap. Yet it is in the 
proper place to be very suggestive of the infratemporal fossa of higher 
reptiles as has been mentioned by several authors (Seeley, ’89; Wood¬ 
ward, ’98, p. 148, and others). 
Ichthyosauria .— The Ichthyosaurs, so far as is indicated by the 
Fig. G. — Dorsal view of the left posterior part of the skull in Ichthyosaurus 
acutirostris, from Zittel after Owen. F., frontal; Pa., parietal; Pf., prefron¬ 
tal; Sq., squamosal; St., supratemporal. 
temporal region, stand closest of all reptiles to the Cotylosauria. The 
supratemporal (figs. G, H, I, St.) is separated anteriorly from the 
parietal by a vacuity, the supratemporal fossa, but there cannot be 
any doubt as to the homologies of supratemporal, squamosal (Sq.), 
and quadratojugal (Qj.) since, in other respects, these have the same 
relations as in the Cotylosaurs. The supratemporal (squamosal, 
Auctorum) joins anteriorly the postfrontal (Pf.), laterally the squa¬ 
mosal, and posteriorly is produced medially to reach the parietal. 
The squamosal articulates anteriorly with the postorbital, laterally 
