DEVELOPMENT OE THE SKULL IN THE BATKACHIA. 
605 
three swinging-points by which the first postoral is yoked on to the preoral bar in the 
Batrachia *. 
On the Structure and Development of the Skull in the Common 
Toad (Bufo vulgaris). — Last stage , adult. 
The figures illustrating the skull of the adult Toad show a chondrosteous structure, 
the chondrocranium with its soft tracts and its partially calcified and wholly ossified 
territories ; the investing bones are faintly indicated by outlines. 
For these latter bones are of much less morphological importance than the parts they 
cover in, being deep or shallow strata of connective fibrous tissue converted into regular 
bony tracts; the essential primary skull is early formed in hyaline cartilage, and 
tracing the development and modification of its elements is the difficult part of work of 
this kind. 
This structure is now entirely continuous, with the exception of the antero-superior 
labials (Plate 54. figs. 3, 5, 6, u.l.'), and has been made up of the parachordal region, the 
whole of the foremost pair of bars (trabeculae), the upper part of the first postoral 
(palato-quadrate), the impacted ear-sac, and the postero-superior labials. The main 
part, or cranial cavity, is an irregular trough or barge, which is flat above (fig. 3) and 
convex below (fig. 4). The lower surface is filled in by cartilage, with certain passages 
. infero-laterally ; whilst the upper surface is covered in in front, behind the middle, and 
near the end. Under the deck-like ethmoidal roof the cranial cavity is bored bv 
the olfactory crura ; behind, the great cavity is wide open for the large medulla 
spinalis. 
In front, the entire bony girdle is the ethmoid, trespassing upon the orbito- and pre- 
sphenoidal regions, which do not differentiate any proper bony tracts. The posterior 
sphenoid also gains the “ larger wings ” merely as an ongrowth of the large prootics 
('pro.). For here we see that the Batrachian skull takes an intermediate position 
between the Elasmobranchs, which have only a somewhat calcified chondrocranium, 
and the Teleostei, whose osteocranium is made up of many special bony territories. 
Here are no calcareous tesserae, as in the Shark ; but there is some disposition to the 
gathering together of the’ calcified tracts into larger plots, that, if finished within and 
without, would answer to the ordinary osteocranial bones. The girdle-bone ( eth .) answers 
to so much of the mammalian ethmoid as would exist if bony matter were to surround 
the olfactory recesses (in that class multiperforate), run a little backwards into the fore 
edge of the anterior sphenoid, and harden a moderate tract of the perpendicular eth- 
moid. Here, in the Batrachian, we have these parts devoid of all those coiled outgrowths 
* These two bars may be conjugated at five different points in the Vertebrata, namely, 1st, by the palato- 
trabecular or “ antorbital ; ” 2ndly, by the orbital process, as in the Toad and Lamprey; 3rd, by the pedicle 
of the mandible ; 4th, by the junction of the basipterygoids (external pterygoids) with the pterygoid bone ; and 
5th, by a sliding joint of the pterygo-palatine arcade (in its mesopterygoid region) on the trabecular beam, as 
in Birds. 
