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THE ENDODERMAL DERIVATIVES 



Pouch (Endoderm 



Arch (Mesoderm) 



Cleft (Ectoderm and 



Endoderm) 



Groove ( Ectoderm ) 



Visceral pouch II 



(Branchial pouch I) 



Visceral pouch III 



(Branchial pouch II) 



Visceral pouch IV 



(Branchial pouch III) 



Visceral pouch V 



(Branchial pouch IV) 



Visceral arch II — hyoid 

 (Aortic arch II) 

 (Opercular fold arises at 

 9 mm. stage, covers 

 gills at 10 mm. stage) 



Visceral cleft II 



(Branchial cleft I) 

 Visceral arch III 



(Branchial arch I) 

 (Aortic arch III — ca- 

 rotid) 



(External gill at 5 mm. 

 stage) 



Visceral cleft III 



(Branchial cleft II) 

 Visceral arch IV 



(Branchial arch II) 

 (Aortic arch IV — sys- 

 temic) 



(External gill II at 5 

 mm. stage) 



Visceral cleft IV 



(Branchial cleft III) 

 Visceral arch V 



(Branchial arch III) 

 (Aortic arch V) 

 (External gill III at 6 

 mm. stage) 



Visceral cleft V 



(Branchial cleft IV) 

 Visceral arch VI 



(Branchial arch IV) 

 (Aortic arch VI — pul- 

 monary) 



Visceral groove II 



(Branchial groove I) 



Visceral groove III 



(Branchial groove II) 



Visceral groove IV 



(Branchial groove III) 



Visceral groove V 



(Branchial groove IV) 



The first four pairs of branchial clefts constitute channels or gill 

 slits from the pharynx to the exterior, and are lined with both ecto- 

 derm and endoderm. The first visceral (hyomandibular) cleft and the 

 sixth visceral cleft are rudimentary in that they rarely open through to 

 the outside. 



