1879.] 



Skull and its Nerves in the Green Turtle. 



345 



Also the epi-hyal is in a low state of development; there is a 

 cerato-hyal and a basi-hyal piece, growing forward below, in front of 

 the large lingual (" basi-branchial ") cartilage. 



But there is a copious growth of external cartilage both around the 

 terminal mouth and around the huge branchial pharynx ; the cranial 

 box is at a low state of development, and the fore part of the head 

 shows no trace of a pre-oral arch. 



In tadpoles we have a very similar state of things, but there is a 

 real ascent; the suspensorium develops a quadrate condyle, and on this 

 the passive mandible is hinged. 



Round the mouth, cartilages quite like those of the lamprey, are 

 developed, but they are smaller ; and there are only four bars 

 (pouches) in the walls of the pharynx ; rudiments of four true intra- 

 brancliials also, are developed. A fifth subcutaneous cartilage appears 

 during metamorphosis, belonging to the mandibular arch ; it becomes 

 the cartilaginous " annulus tympanicus." 



After it has appeared the " styloid cartilage " of the lamprey 

 ("epi-hyal") is, in them, slowly developed, and becomes the "colu- 

 mella auris." 



Also, during metamorphosis, the rudiment of a " palatine " visceral 

 arch appears, and in the genus Bufo becomes a large distinct pre-oral 

 cartilage. After metamorphosis, another cartilage appears on each 

 side, within the nasal cleft, the " pro-rhinal." 



My idea of the order, in time, of the skeletal elements is as fol- 

 lows : — ■ 



First. The superficial cartilages of the mouth and respiratory 

 pharynx. 



Secondly. Basi-neural, and then, afterwards, going from them, 

 visceral cartilages, in the inner layer of the walls of the mouth and 

 throat. 



Thirdly. After that, selection of dermal scutes, first as scales and 

 afterwards as splint-bones (" parostoses "), to supplement, for support- 

 ing purposes, the chondro-cranium. 



Fourthly. A gradual arrest, and then more or less of suppression, 

 of the chondro-cranial parts, and the increased use of subcutaneous 

 investing bones, at times in conjunction with remnants of the old 

 primary superficial cartilages. 



The development of the spine has been, I believe, a thing of later 

 date ; and the limb-girdles and limbs newest and latest of all. 



The brain, mouth, and throat, with coiled intestines, whose outlet 

 is very little behind the occiput, make up all that is of any con- 

 sequence, in such a form as the gigantic tadpole of the paradoxical 

 frog (Pseudis) ; whose post-cranial segments have evidently been 

 super-additions, developed for the sake of locomotion — to form 

 a mere swimming organ. 



