574 



REPTILIA. 



are studded on eaeli side with cartilaginous points ; and the arches 

 1 and 4 have similar points on one side only, so that when the 

 arches are approximated, as they can be by an elaborate temporary 

 set of muscles provided for the purpose, the cartilaginous teeth 

 lock into each other so accurately, that the branchial fissures are 

 completely and firmly closed ; a provision which is evidently 

 indispensable, in order to allow the tadpole to fill its lungs with 

 air. 



The above is the condition of the branchial portion of the hyoid 

 apparatus before the metamorphosis of the tadpole has made much 

 progress ; and from this time a series of changes begin of a most 

 curious and interesting description. 



When the me- rig. 260. 



tamorphosis has 

 commenced, the 

 os hyoides and 

 branchial arches 

 assume the ap- 

 pearance repre- 

 sented at Jig. 

 260, B. The 

 pieces 8 and 9 

 are no longer 

 both cartilagi- 

 nous, the latter 

 having become 

 entirely ossified. The branchial arch 1 is likewise converted into 

 bone ; and its upper surface, being considerably enlarged, is now 

 connected with both the pieces marked 10 and 11. The three 

 cartilaginous pieces 5, 6, 7, in Jig. 260, A, are consolidated into 

 one, while the branchial arches 2, 3, 4, become much reduced in 

 size, the branchiae approach each other, and the cartilaginous points 

 with which they are provided adhere together, so that from hour to 

 hour, so to speak, the mass (2, 3, 4) composed of the three united 

 branchial arches becomes insensibly obliterated, and in a very few 

 days is entirely absorbed. While this absorption is going on, the 

 branchial arch 1 assumes greater consistency, its inferior extremity 

 becomes directed outwards, and it loses the little cartilaginous 

 teeth previously appended to it ; the os hyoides thus assumes the 

 simple form represented in Jig. 260, c. Lastly, the cartilage 6 

 disappears, and the complex branchial apparatus of the tadpole be- 



