IX.] 



THE MAXILLARY PROCESS. 



229 



appears when taken by itself somewhat remarkable, and led 

 to the view, formerly very general and still held by many, 

 that the superior maxillary process was equivalent to a 

 visceral arch. Mr Parker has recently shewn that in both 

 Osseous fishes and the Elasmobranchii all the anterior arches 

 undergo a somewhat similar segmentation, and it appears 

 therefore to be a fair deduction that this segmentation 

 persists in the chick in the mandibular arch, while it has 

 been lost in the others. None of Mr Parker's iuvestigations 

 on the lower vertebrates support the view that the maxillary 

 process is an aborted anterior arch. Similar views as to the 

 nature of the maxillary process have been arrived at by 

 Gegenbaur (loc. cit), from his investigations upon the crania 

 of the cartilaginous Fishes. 



7. The cartilage or differentiated mesoblast appears in 

 the maxillary process later than in the mandibular arch, 



Fig. 69. 



Cvr 



View from below of the Paired Appendages of the Skull of a Fowl 

 on the Fourth Day of Incubation. (From Parker.) 



cv 1 cerebral vesicles, e eye. //i fronto-nasal process, n nasal pit. tr trabecular 

 pts pituitary space, mr superior maxillary process, pg pterygoid, pa pala- 

 tine, q quadrate, mk Meckel's cartilage, ch cerato-hyal. bh basi-hyal. 

 ebr ceratobrancbial. ebr proximal portion of the cartilage in the third 

 visceral arch. bbr. basibranchial. 1 first visceral cleft. 2 second visceral clef t. 

 3 third visceral arch. 



