130 ANNALS NEW YORK ACADEMY OF SCIENCES 



seems to show a place where the depressor could have been attached. The 

 origin of the depressor would have been on the squamosal, alongside the 

 otic notch, since in the Anura the origin is on the posterior limb of the 

 squamosal and on the tympanic annulus. The Anura have a second part 

 of the depressor arising from the dorsal fascia, and Eryops also could 

 well have had this second part of the depressor. 



From the inferred arrangement of the muscles in Eryops, perhaps 

 some explanation may be given of the changes and losses that have taken 

 place in the anuran skull. First, the capiti-mandibularis medius was no 

 doubt attached to the parietal region and the capiti-mandibularis super- 

 ficialis to the squamosal. To accomit for the open condition of the tem- 

 poral roof in the Anura and for the loss of the tabulare, supratemporal, 

 squamosal, postfrontal and postorbital, we may adopt the hypothesis that 

 these muscles were pulling against one another; that the region between 

 them gave way and made breaks and openings which did not exist in the 

 primitive form with its unbroken temporal covering. The region be- 

 tween the parietal and the squamosal would lie between the pulls of these 

 muscles and the first break w^ould appear here. The disappearance of 

 the dermosupraoccipitals, tabulars and supratemporals was probably cor- 

 related with the opening out of the temporal region and with the exten- 

 sion of the temporal muscles up on to the top of the skull. 



Labidosaurus 

 Plate XII, Figs. 2, 3, 4 



This primitive cotylosaur shows the covered or roofed temporal region, 

 which it has inherited from the Stegocephalia and from such fishes as 

 Osteolepis, Polypterus and Amia, in which the dermal bones are still in 

 their primitive position in the skin and not sunken below it. The quad- 

 rate is fixed, so that in that region there is no movement. The stout 

 teeth demand strong jaw muscles and there is ample room for a large 

 capiti-mandilndaris beneath the temporal roof. The massive lower jaw 

 with its large suprameckelian fossa also requires large muscles. The 

 pterygoid region and the base of the brain case are essentially similar to 

 those of Splienodon and imply a corresponding similarity in the pterygoid 

 muscles. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY Y^) 



Capiti-mandibularis superficialis (C. m. s.). 

 Capiti-mandibularis medius (C. m. m.). 



