408 H. B. POLLARD, 



sthotic or craniospinal process, in the following manner. From the 

 outside of the uppermost end of the piocess a ligament passes to its 

 lateral edge, underneath a supratemporal. From the inside of the 

 process a stouter ligament passes to its posterior third. This liga- 

 ment in older animals becomes completely ossified. At 

 its anterior edge the posttemporal scale is bound to the supratemporals 

 by the ordinary ligaments of the scales while anteroiuteriorly it projects 

 some way internally becoming attached by ligament to the squamosal 

 process. At its posteroexternal edge is attached the ligament which sup- 

 ports the supraclavicle (fig. 14) though the latter is also attached to the 

 craniospinal process. The praeoperculum, as I have called the cheek 

 bone, consists, as Agassiz first showed, of two parts which in Anda be- 

 come separate one being the prcopercular and the other the lower 

 postorbital. Beneath it lie one or (secondarily) two bones which 

 correspond with the piscine socalled jugal. 



The operculum is borne by the bent hyoman di b ular. 

 The latter is attached by ligament to the stylohyal but also by a 

 quadrato hyomandibular ligament to the quadrate. This ligament 

 however proceeds downwards and backwards so that the quadrate 

 really supports the hyomandibular and not vice versa. The upper 

 articulation of the hyomandibular is very slight and not well marked. 

 Its bent form is specially shaped to suit such a function. 



Comparison with the Stegocephali. 



The relationship of the primordial cranium of Polypterus with 

 that of Urodelcs and Anura leads naturally to a comparison of the 

 dermal bones of Polypterus and the Stegocephali, the ancestors in ge- 

 neral of the Amphibia. 



In Polypterus there is no prefrontal, the ectethmoid taking its 

 place. Its anterior suborbital represents the lachrymal while its po- 

 sterior suborbital is the postorbital of Stegocephali. There is no median 

 ethmoid in the latter. 



In the squamosal region the homologies are no longer so easy to 

 see. First in Polypterus it must be noticed that in comparison with 

 certain of the Devonian fish, especially Osteolepis, the opercular series 

 has become elongated and has acquired more independence than it had 

 in its fossil representatives, at the same time extending further back- 

 wards. The operculum in Polypterus is borne by the hyomandibular 

 which in turn is a I have shown above chiefly sustained by the quadrate 

 eventually. Supposing the hyomandibular to become lost, or fused with 



