114 BULLETIN OF THE ESSEX INSTITUTE. 



cartilage. To attempt to homologize a membrane bone 

 with a cartilage is a difficult task. If, however, it be 

 maintained that we have here a case of substitution such 

 as exists in the roofing bones (parietals, frontals, etc.) of 

 the cranium, in which the cartilaginous roof of the brain 

 cavity becomes replaced by the immigration ot dermal 

 bones, Ichthyophis throws considerable light upon the 

 question. In this form the palatine bone (part of the 

 maxillopalatine process of the Sarasins), which is distinct 

 in early stages, arises, not in connection with the cartilag- 

 inous process in question, but with the nodule of carti- 

 lage shown in Figs. 22, 23, and 24, j9c. In Ichthyophis 

 not only is this true cartilaginous ' palatine ' present but the 

 antorbital process occurs as well. 



If we adopt the usually accepted homologies (which, 

 however, are not beyond question) the palatine of tbe 

 higher vertebrates is to be sought in the anterior portion 

 of the upper jaw of the Elasmobranchs, which is accord- 

 ingly called the palato-pterygo-quadrate or some similar 

 terra, implying homologies with the palatine of higher 

 forms. In these very Elasmobranchs, however, the exact 

 homologue of this antorbital process exists, in no way 

 connected with the upper jaw but rather as forming a part 

 of the nasal capsule. 



The transformation during metamorphosis from a con- 

 dition in which the jaw of a small suctorial mouth articu- 

 lates with the anterior end of the pterygoid cartilage to 

 one in which it reaches back to the body of the quadrate 

 beneath the middle of the otic capsule is one of the most 

 striking characteristics of the Anuran chondrocranium. 

 Another of its distinctive features is found in the auditory 

 apparatus. While in the Urodela the fenestra ovalis may 

 be occupied by a cartilaginous stapes which may or may 

 not be connected with the quadrate by a stapedial process, 



