336 Mr. W. K. Parker on the Structure ^c. of [Nov. 23 



bell-flower, and having its broad-lipped end attached, like a snail's foot, to 

 the top of the back of the suspensorium, and its small roundish end, or 

 apex, set in a neat bony cup that grows from the face of the stapes. 



Nevertheless the " spiracle" or " tympano-Eustachian cleft," is scarcely 

 at all apparent in the TJrodeles ; in the Batrachia it is large within, but 

 never fairly open externally. 



In the Urodeles I miss entirely the copious labial growth of cartilage 

 outside the true visceral arches ; and although Siren lacertina has horn 

 on its jaws, I feel certain that its mouth is never suctorial even in a very 

 early stage. 



It is not suctorial in the " Aglossal Toads," as I have recently shown, 

 but they have a rich growth of labial cartilages. 



There are some more very important facts in the morphology of the 

 skull in the Urodeles that I am anxious to lay before the Society. 



The nasal roofs are free, independent " paraneurals," and not mere 

 outgrowths of the trabeculce ; thus they correspond with the eyeballs and 

 ear- capsules. 



The trabeculse cranii appear much later than in the Batrachia, and are 

 at first (a) relatively much smaller, and (b) have three or four times as 

 much of their substance situated jxiracJiordallT/. 



The hinder half of the basilar plate, or " investing mass," is formed as 

 a pair of distinct cartilages. The trabeculse chondrify four or five days 

 later than the visceral arches, and the " parachordals " ten or twelve 

 days later than the trabculae. 



My earhest observations of the notochord, in unhatched Axolotl " fry," 

 show only a moderate downbend of the apex of the notochord. 



But Mr. Balfour's observations show that in Selachians it is like a 

 sheep-hook ; mine, on older embryos, show a moniliform condition of the 

 notochord in front, seemingly due to pressure in growth against the 

 pituitary gland. ;, 



I have not seen in Amphibia what Grotte show^s in the Bombinator 

 Toad, namely, a cartilaginous notochordal sheath; this is well seen, 

 however, in embryo sharks and rays. 



But nothing seen in sharks and rays is more suggestive than what I 

 am in this paper describing in the Urodeles, for they form tivo rudimen- 

 tary verfehral centra behind the pituitary body. 



Besides this, in several kinds, that part of the notochord which, in the 

 " Sauropsida," is jammed in betw^een the inves ting-mass cartilage, where it 

 forms the median occipital condyle, is in certain Urodeles formed into a 

 small, imperfect, intercalary vertebra. 



This vertebra is formed of a pair of " parachordal " patches of carti- 

 lage and a tract of notochord which gets its own bony sheath ; the side 

 pieces ossify independently (in Sjjelerpes rubra), and then coalesce with 

 the anterior part of the notochordal segment. 



"We have thusj in front of the vertebra which serves as the " atlas " 



