THE CHONDKOCRANIUM IN THE ICHTHYOPSIDA. 127 



ponding stages in the development of the two forms would 

 show a still more marked similarity. The otic capsules 

 are connected dorsally by a solid synotic tectum and ven- 

 trally by an unbroken basilar plate formed by the fusion 

 of the parachordals aroiind the anterior end of the uoto- 

 chord. The median wall of the otic capsule is either ab- 

 sent or but slightly developed. Neither fenestra ovalis 

 nor stapes occurs. 



The trabecule unite ventrally into a median band in 

 front of the hypophysis and continue forward to the end 

 of the skull. At its anterior end the trabecular band 

 broadens out into the ethmoid plate which forms the floor 

 of the nasal capsules. Supraorbital bands extend for- 

 ward from the anterior ends of the otic capsules to the 

 lateral margins of the tegmen cranii which roofs over the 

 anterior portion of the brain cavity. 



The palato-pterygo-quadrate cartilage extends from the 

 lateral margin of the ethmoid plate backward to beneath 

 the anterior end of the otic capsule. Its posterior end is 

 supported to a greater or less degree by the ventral end 

 of the hyomandibular cartilage which has its dorsal end 

 closely applied against the outer wall of the otic capsule. 

 Meckel's cartilage articulates with the ventral surface of 

 the quadrate portion of the palato-pterygo-quadrate car- 

 tilage. 



In discussing the relations of Polypterus to the Batra- 

 chia, Pollard said, "On comparing the primordial cranium 

 of a young Polypterus with that of Urodeles, the general 

 resemblance is seen to be so ofreat that an anatomist see- 

 ing it alone for the first time would certainly place it 

 among the latter." Considering the features which dis- 

 tinguish the chondrocranium of Polypterus in common 

 with the rest of the Fishes from that of the Batrachia, as 

 outlined in the preceding pages, so great a similarity can 



