DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
15 
ON THE TVPICAL BATRACHIAN SKULL. 
In the following descriptions I shall take the skull of Ranct temporaria as the 
“norma” or pattern form ; it is the best on the whole ; one or two exceptional cha¬ 
racters exist in it, viz.: the mark of the originally separate metapterygoid (a rare 
character); the annulus tympanus is not perfect until old age; and the stylo-hyal is a 
long while fusing with the floor of the skull and ear-capsule, if indeed it ever becomes 
fused ; but, with these exceptions, this may be taken as the highest kind of Batrachian 
skull, and the best rule to measure the others by. 
ON THE EARLY STAGES OF THE BATRACHIAN SKULL. 
No known kind of Vertebrate shows so many and such instructive stages in its 
development as the Batrachian. 
The skull of the newly-hatched embryo of the common Frog or Toad is strictly 
comparable to that of a larval Lamprey ( Ammocostes ), whilst that of the well-grown 
Tadpole comes very close to the skull of the adult Petromyzon. 
But whilst the ordinary Batrachia have a very Petromyzine or suctorial larva, the 
“ Aglossa ” in their early stages have a cranium and face very similar to what is seen 
in the “Siluroid” Teleostean Fishes, and their skull suggests to the observer the most 
probable form of endocranium likely to have existed in such Ganoids as Pterichthys 
and Coccosteus. 
Both these kinds of larval endocranium ( chonclrocranium ) are figured in my 
“Batrachian Skull,” Part II. (Phil. Trans., 1876, Plates 54 and 55, Bufo vulgaris; 
Plates 56-58, Dcictylethra; and Plate 60, fig. 3, Pipa). 
My present business is with the suctorial type of larval Batrachian skull; for full 
details and figures of the wide-mouthed Siluriform type of skull I must refer the 
reader to the paper just referred to. 
My most successful dissection of the earliest cartilaginous skull in these types was 
that of Bufo vulgaris (op. cit., Plate 55, figs. 1, 2); the embryo was 4 lines (^rd of 
an inch) in total length; the next to this (Plate 55, fig. 3) was of a Tadpole of the 
same species, 5 lines long. 
I shall make the first of these my First Stage, referring the reader to the plates in 
the published paper. 
Of the skull in more advanced stages the present work will give many instances 
and illustrations ; after describing the simple foundation, as seen in Bufo, I shall 
describe a series of stages in various species of the genus Rana. 
The larval skulls-of other types will be described in their proper order, with the 
adult condition of the skull in the same and other species. 
