172 PEOF. W. K. PAEKEE ON THE STEUCTUEE AND 



The Skull of Sieboldia maxima mas adultus, 4 feet 2 inches long. 



The general form of this skull (Pis. XXXVI. & XXXVII.) is semielliptical and 

 very flat ; the greatest breadth is across the quadrate condyles ; and this measurement 

 is about one tenth greater than the length along the axis. The maxillary arch reaches 

 outwards so far as to give a measurement just intermediate between the length and 

 the greatest breadth ; its backward stretch is only halfway from the fore margin to the 

 condyle of the corresponding quadrate. 



The direction of those condyles is outwards, a little downwards, and slightly back- 

 wards ; behind they reach as far as to be opposite the narrowed waist of the occipital 

 cincture. 



Generally speaking, the skull is subconvex above, and gently hollow below ; but 

 there is, notwithstanding the persistence of the fronial and sagittal sutures, a definite, 

 rather sharp, median crest. 



The whole maxillo-premaxillary arc is ankylosed into a single bone ; the palatines 

 and vomers of the same side are confluent ; and the parasphenoid has coalesced with 

 the occipital bones below : this is due to the great age of this individual. The pub- 

 lished figures do not show this\ 



On the whole, the metamorphism of this skull has been arrested at the same stage 

 as that of an ordinary " Caducibranch " of the first summer, or immediately after the 

 loss of the gills. See Plate XL. figs. 6 & 7. 



A. The Investing Bones of Sieboldia. 



The superficial bones are dense, smooth, and often perforated by vessels ; they have 

 a considerable thickness in several instances ; and they form about half the materials of 

 the building. But there is no definite line to be drawn between those investing bones 

 that keep entirely free from the chondrocranial tracts and those that graft themselves 

 upon certain parts of those tracts : for instance, the palatine keeps free from the 

 cartilage ; but its segmented pterygoid process (the " pterygoid " of the adult) ossifies 

 all the proximal part of the pterygoid outgrowth of the suspensorium. 



The three pairs of submesial roof-bones (parietals, frontals, and nasals) reach from 

 the foramen magnum to the outer nostrils (PI. XXXVI. fig. l,jp,f, n, e. n), and form 

 an oblong tract which only partially hides the underlying structures; for the endo- 

 cranium is spread out below, and contracted at the top of the low side walls. These 

 symmetrical upper plates are all imbricated from before backwards ; and the parietals {p) 

 have only their square hinder part, or about two fifths of their length, free from the 

 overlapping frontals (_/"). The fore part of each becomes a long, sharp, slightly out- 

 turned wedge of bone. 



' ' Fauna Japonica,' pi. viii. figs. 1, 2; Wiedersheim (6), pi. ii. figs. 21, 22. 



' One of the lesser Japanese Urodeles, viz. Onychodattylus, undergoes less metamorphism than this gigantic 

 kind (see Trans. Linn. Soc, Zool. 1880, pi. six. figs. l-<5). 



