THE SKULL. 



585 



mouth. The greater part of the arch, parallel with the trabeculae, 

 is equivalent to what has been called in the Axolotl the 



U.I 



FIG. 338. TADPOLE OF COMMON TOAD, ONE-THIRD OF AN INCH LONG ; 

 CRANIAL AND MANDIBULAR CARTILAGES SEEN FROM ABOVE ; THE PARACHORDAL 



CARTILAGES ARE NOT YET DEFINITE. (From Parker.) 



nc. notochord ; ins. muscular segments ; au. auditory capsule ; py. region of 

 pituitary body; tr. trabecula; c.tr. cornu trabeculas ; p.pg. palatopterygoid bar ; pd. 

 pedicle; q. quadrate condyle ; mk. Meckelian piece of mandibular arch; s.o.f. 

 subocular fenestra ; u.l. upper labial cartilage. The dotted circle within the quadrate 

 region indicates the position of the internal nostril. 



quadrate, while its anterior attachment to the trabeculae is the 

 rudiment of the palato-pterygoid cartilage. The posterior 

 attachment is known as the pedicle. 



The condition of the mandibular arch during this and the next stage 

 (fig- 339) is very perplexing. Its structure appears adapted in some way to 

 support the suctorial mouth of the Tadpole. 



Reasons have been offered in a previous part of this volume for sup- 

 posing that the suctorial mouth of the Tadpole is probably not simply a 

 structure secondarily acquired by this larva, but is an organ inherited from 

 an ancestor provided through life with a suctorial mouth. 



The question thus arises, is the peculiar modification of the mandibular 

 arch of the Tadpole an inherited or an acquired feature ? 



If the first alternative is accepted we should have to admit that the 

 mandibular arch became first of all modified in connection with the 

 suctorial mouth, before it was converted into the jaws of the Gnatho- 

 stomata ; and that the peculiar history of this arch in the Tadpole is a 

 more or less true record of its phylogenetic development. In favour of this 



