202 PROr. W. K. PARKER ON THE STRUCTURE AND 



Skull of a " Cryptohranchiate " Larva of Triton cristatus, 2 J inches long. 



A. Investing Bones. 

 The superficial bones are very much larger and stronger in this larva, which has 

 almost lost its gills ; it is now in a state very nearly corresponding to that of the adult 

 Sieholdia and Menopoma. 



Lengthwise the roof-bones (PI. XL. fig. 6, fp) are not much more extended ; but 

 they are much broader, so as to overlie the walls well ; and thus their form is a shorter 

 oblong. 



The fore part of the interorbital region was broader than the hinder ; now the reverse 

 is the case ; the temporal angles of the parietals are still short and blunt. 



On the antero-external angle of each frontal a small triangular bone is now seen 

 close behind the nasal ; this is the prefrontal {p.f). The nasals («) are large crescents 

 now, three or four times as broad as they were in the last stage. 



The squamosals {sq) have now a more even breadth downwards, and are much more 

 solid. The premaxillary {px) is much wider on its palatine aspect; and the bony 

 falcate nasal processes (fig. 6, n. px) are broader, and their interspace is filled up under 

 the fossa, in the fore half of the bone. There is a large maxillary {mx) on each side 

 now; each bone is falcate, has an ascending process (fig. 6), and is as long as the 

 median single premaxillary. 



The broadly falcate vomers (fig. 7, v) cover more of the trabecular cornua {c. tr), have 

 a more definite notch inside the inner nostril {i. «), and are now perfectly distinct from 

 the palatines {pa). These latter bones are divided from the vomers by a subtransverse 

 suture, and are now parallel with the axis of the skull, and are pointed behind ; but 

 they are relatively less than they were in the first stage (fig. 1, pa, v). 



The reason of this is that the edentulous pterygoid part (pg) has become segmented 

 off from the tooth-bearing palatine, and has retreated so far back that the fore edge is 

 nearly under the middle of the orbital space. 



It is now much broader and shorter than it was when continuous with the palatine ; 

 and its fore end has diverged out to some distance from the skull : it is turning out- 

 wards, whereas it was directed inwards. The form now is somewhat like the outline of 

 an hourglass ; but the hind part is much the broader, and now lines twice as much of the 

 suspensorium ; the fore end is ragged ; the base is grooved above for a new process of 

 cartilage [e.pg). The palatine bones are not ankylosed with the vomers, but the whole 

 palate is Menopomine. 



The parasphenoid (fig. 7, pa.s) is relatively larger. In front it nearly reaches to the 

 fore margin of the intertrabecular notch (c. tr, i.u. c) ; behind it actually forms part of the 

 foramen magnum (/. m) ; it has also developed outwards, forming the temporal angles. 

 None of the inner skull is seen outside it below ; and the roof-bones overlap the 

 endocranium above. The bones are altogether stronger and smoother. 



