No. 434] THE AMERICAN PELYCOSAURIA. ioi 



united, first partially (Cynognathus crateronotus and Procolophon) 

 and finally completely (C. platyceps and Galesaurus). Notable is 

 the position assumed by the squamosal portion of the psq + sq ; 

 as shown above in the description of the forms it is spread out as 

 a thin film upon the surface of the cranial wall formed by the 

 developing of the parietals, so that it was firmly held by its 

 application to the skull wall as in the mammalian temporal and 

 is free only at its lower extremity. From this free extremity of 

 the squamosal portion the prosquamosal portion extends forward 

 almost at right angles, the quadrate and quadrat o-jugal are 

 probably concealed beneath the point of union of the two and the 

 quadrate is so far overwhelmed that the lower end <>f the psq - sq 

 comes into articular compact with the articular. 



This structure perhaps presents the best mechanism to resist 

 the strain imposed upon the quadrate in biting; it is straight up 

 against the lower end of a bone fastened to the skull by nearly 

 its full length and its parallel to the strongest attachment. That 



