DEVELOPMENT OP THE SKULL Df THE UEODELES. 201 



of the arches are formed into a " colander " by interdigitating conical papillae of simple 

 cartilage clothed with epithelium; in the larva of the " Anura" such processes grow 

 into ridges, and become clothed with a rich tufted growth of true internal hypohlastic 

 branchiae. 



The basal pieces are two in number, and grow so far back behind their own proper 

 arches as to suggest an ancestry for these types with a much greater number of bran- 

 chial arches and a more complex " vagus " nerve. 



The first piece [l.br^) is a thick, high bar, rounded and lessened in front, where it 

 joins together the hyoid bars, thick where it joins the first ceratobranchials, and thin 

 again where it conjugates the second ceratobranchials. Under its pointed end the 

 second piece {b.lr^) is articulated ; it is a fiat bar, becoming wider at the middle, and 

 then fish-tailed at the end ; the hinder three fifths is bony. 



D. Comparison of the larval Newt's Skull with that of other Types. 

 In some respects this skull is on a level with that of the lowest "Proteidea" — 

 Proteus, Menobranchus, Siren; in others with more metamorphosed types, such as 

 Sieboldia and Menopoma. 



Like the larvae of some other " Caducibranchs," e. g. Spelerpes, it shows well the 

 formation of the "odontoid" rudiment; and it comes in conveniently to explain the 

 "sphenotic" horn of Siren. It agrees with Siredon, and not with the Proteidea just 

 mentioned, in having only the ascending process confluent with the endocranium, the 

 lower lobe or " pedicle " proper being free, and articulating with an outgrowth of the 

 basal plate, a parachordo-trabeciiJar growth. 



This evident preauditory mass, which projects beyond the angle of the parasphenoid, 

 is the counterpart of the cartilaginous facet for the shortened " pedicle " of the adult 

 Frog, and of the postsphenoidal outgrowth (or " basipterygoid ") of Lepidosteus. 



In each of these types the basis cranii grows out to meet a free pedicle — primarily 

 free in this Urodele and in Lepidosteus, but secondarily free in the "Anura." 



Afterwards, as we ascend the scale, the pedicle is absorbed, more or less, and the 

 otic process is developed at its expense ; then the pterygoid bones acquire a carti- 

 laginous facet and articulate with the basipterygoids. 



Lastly, in Mammals we see these latter processes indifferently ali- or §«s?'-sphenoidal, 

 and having the pterygoid bones applied to them by a squamous suture without the 

 intervention of cartilaginous plates to form a joint. 



At present in this larva nearly half the endocranium has a finished floor ; the short 

 part in front is a non-segmented intertrabecular tract. That azygous element has its 

 least development, and least distinctness, in the Urodeles. 



