SKPLL OF CURYSOCHLORIS. 



451 



The frontal is relatively smalt, being only about half the size 

 of the parietal. There is a distinct orbital constriction. 



The large parietals each form nearly a quarter of the upper 

 surface of the skull. Each articulates with its neighbour, and 

 with the frontal, squamosal, tabular, and supraoccipital. 



The squamosal is of moderate size but very peculiarly shaped. 

 The upper squamous portion is much reduced, and behind the 

 glenoid cavity there is a long posterior descending process which 

 covers the petrosal and extends as far as the exoccipital. In 

 front the squamosal articulates with the maxilla, but forms 

 practically no part of the zygoma. 



On the base of the skull the palatines, pterygoids, tympanies, 

 auditory ossicles, vomer, basisphenoid, and basioccipital and 

 exoccipital can be readily made out, but their relations and 

 structure can be better understood from the reconstruction of 

 the earlier stage. 



Text-figure 1. 



~Pcf. 



A. Occiput of young Chrysochloris asiaiira. X -i. 



B. Occiput of young Hemicentetes sp. X 3'o. 



For explanation of lettering see p. 4-58. 



It is necessary, however, to consider more fully the structure 

 of the occiput, as it is unlike that of any other known mammal. 

 When the skull is examined posteriorly there is seen to be a 

 very small basioccipital, a pair of small exoccipitals, and a 

 relatively large supraoccipital, with no distinct interparietal. 

 The relations and shapes of these will be seen in text-fig. 1. 

 On each outer side of the supraoccipital is a rounded bone of 

 moderate size which I regard as the tabular. It is a membrane- 

 bone which articulates with the supraoccipital, the parietal, the 

 exoccipital, and partly covers the petrosal or periotic. At this 

 stage it does not c^uite reach the squamosal, but not improbably 

 in a slightly more advanced stage it may be found to articulate 

 with the squamosal. Whatever be the nature of this bone, it 

 quite certainly, as will be seen later, is not formed from anv pai-t 

 of the ear-capsule, and as it certainly occupies the exact position 

 of the tabular in Therapsid and other early reptiles, it seems 

 well to apply this name to it. As a large tabular occurs in 



32* 



