DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
29 
Third Stage. —1 (continued). Tadpole of liana clamata (B) 3 inches 5 lines long; 
tail inches long; hind legs, 1 inch long. 
In this stage (Plate 4, figs. 1-4) we see some metamorphic progress beyond the last; 
the general form of this as compared with Stage A (same species) is not much altered 
(see Plate 2, figs. 5-7), but there are some new parts, and some changes in the old. 
The time, indeed, has been short during which these changes have taken place, for 
these Tadpoles even at their height, as larvae, were beginning rapidly to be trans¬ 
formed. The exoccipitals (e.o.) are larger, but the prootics are not visible; outside the 
frontal region the premaxillaries ( px.) have appeared in addition to the three investing 
bones seen in the last stage. But the thing of most importance is the rapid growth ol 
the “ intertrabecula ” as a vertical nasal septum (s.n.), and the solidification of tlle mem¬ 
branous roof of the nasal sacs into a pair of ear-shaped nasal cartilages ( na.) whose 
antero-external notch forms the inner boundary of the outer nostril (na., e.n). These 
elegant shells of cartilage are becoming confluent with the top of the septum internally, 
and with the ethmoidal “wing” ( al.e .), behind: they are true “ paraneurals,” and 
answer to the “ sclerotics ” and “ periotics.” 
Another change is the retreating of the orbitar process away from the side of the 
skull, so that the “post-palatine” rudiment is exposed (or.p., pt.pa.); the “pre-palatine” 
rudiment ( pr.pa .) in front of the internal nostril (i.n.) is also further from the trabecula. 
The fore margin of the chondrocranium is very similar to what it will be 
eventually, but the rounded end of the intertrabecula is still distinct from the 
nasal roofs (s.n., na.), and the cornua trabeculae ( c.tr.) are still undivided at their end. 
The great upper labial ( u.l.) has lost the fenestrse that showed signs of division, 
right and left, and is now, more than ever, one large saddle-like plate.* 
The mandibular and hyoid arches are much in the same state as in the younger 
larvae (Stage A), but the branchials are altering preparatory to extensive absorption. 
Compared with those of the Bull-frog (Second Stage, Plate 2, fig. 8), it will be seen 
* In this and the last two stages (A and B) we have a very instructive analysis, so to speak, of the 
complex nasal capsule in the higher Vertebrates, e.g., of that in the Mammals. It is composed primarily 
of the trabeculae with their lateral (antorbital) wings, where the cranium closes in in front of the vertical 
“ intertrabecular ” middle wall; of the nasal roofs which may grow down into side w T alls ; and of the rich 
outgrowths of turbinals that grow from the front of the antorbital wings of the ethmoid (tipper and 
middle turbinals) ; and from the inside of the outer wall (inferior turbinals). 
Other turbinals may spring from the roof (nasal turbinals of the .Rodents), or inside the outer nostril 
(ali-nasal turbinals of Pig and Bird). 
Then the narial valves are formed of segments or subdivisions of the upper labials, the whole structure 
being roofed by the nasals, floored by the vomer or vomers and palatine plate of the maxillaries, and 
walled in by the maxillaries and premaxillaries. 
Lastly this complex labyrinth of cartilage may, itself, become bony, to a greater or less degree, and even 
may coalesce, more or less, with the investing bones. 
Anyhow, the plan and pattern, and the numbered elements of this labyrinth, are to be seen in their first 
simplicity in the nasal region of the Tadpole. 
