216 



ON THE STRUCTURE OF THE SKULL. 



thus there can be no doubt about the preniaxillae (Pmx), the 

 maxilla (Mx), and the two large-toothed vomers (Vo). The 

 position of the posterior nares between the last-named bones and 

 the bones (PI) taken in connection with the relations of the 

 latter to the prefrontal region of the skull, sufficiently defines 

 the palatine character of PI; while Pt, connected with the 

 palatines on the one hand, and terminating on the inner side of 

 the mandibular suspensorium on the other, corresponds as dis- 

 tinctly with the pterygoids of the higher Vertebrata. 



Fur. 87. 



Fig. 87. — The Cartilaginous Cranium of Rana esculenta. A, from above ; B, from below 



(after Duges). — y, the girdle bone. 



The bone (QJ), which connects the end of the maxilla with 

 the outer side of the suspensorium, appears to correspond with 

 the quadrato-jugal of abranchiate Vertebrata. 



It is more difficult to determine the nature of the bone z, 

 the " temporo-mastoid " of Duges, which is a long, hammer- 

 shaped membrane bone, extending from the skull to the articular 

 surface for the lower jaw, and sending a long process forwards 

 over the temporal region. 



When this bone, the pterygoids, palatine, quadrato-jugal, &c, 

 have been removed, the cartilaginous cranium of the Frog (Fig. 

 87) is seen to give off from the outer ends of the prefrontal region 

 and the auditory protuberances, two prolongations, the anterior 

 of which curves round the orbit, and eventually unites with the 

 posterior in the cartilaginous process which articulates below 

 with the mandible, and unites by its upper or cranial end with 

 the suspensor of the hyoidcan apparatus (St., Fig. 86). 



