DEVELOPMENT OE THE SKULL IN THE BATKACHIA. 
617 
two cartilaginous knuckles form the foundation of the nasal superstructure ; by touching, 
they begin to build the “ internasal plate.” The clubbed ends will be the lower part 
of the nasal labyrinth ; they send out the free “ prorhinals.” The gentle outbend 
of the trabeculae, where the fore part of the next bar conjugates, will lie as the foundation- 
stone to the lateral ethmoid ; it is the antorbital region. These bent rods have the 
cranial bag resting upon them ; the pituitary body dips in front of the end of the noto- 
chord (“Frog’s Skull,” plate iv. tig. 8); and the “third vesicle” lies on the notochord 
and the gelatinous tissue which invests it. 
The first postoral arch (“ first visceral arch ” of embryologists) is bowed and 
bent much after the fashion of the trabecula. Its apical partis bent suddenly inwards ; 
and then the bar, in growing forwards, also turns inwards, subparallel to the other ; but 
curving somewhat outwards, as the trabecula does somewhat inwards, there is a space 
left of an oval form — the “ subocular space,” or “ fenestra ” ( so.f ’.). Before this second 
bar gives off the pterygo-palatine rudiment (ppgf on the other, or outer, side it is 
cupped for the head of the hyoid half-arch. The rest of the main bar then curves 
inwards towards the outbent trabecular horns (c.tr.), and ends in a rounded condyle, 
which fits in the hollow proximal end of the Meckelian bud ( mJc .), an ovoidal nodule 
of cartilage, cupped above and rounded below. This free mandibular rudiment looks 
towards its fellow, and not from it, as in the case of the continuous distal region of the 
trabeculae. The nasal passage lies over this little nodule, and opens into the palate in 
front of the pterygo-palatine rudiment (see figs. 2 & 3). 
The next arch, whose lower half only is developed, corresponds now to the lower piece 
in the hyoid of a Shark, and to the whole of what appears in a tailed Amphibian 
(Huxley, “ On Menobranclms ,” plate xxix. Hy , plate xxx. Cli). Its low position corre- 
sponds with that of its homologue in the adult Osseous Fish (“ Salmon’s Skull,” plate vi. 
ep.h., c.h.). In that type it has descended gradually, after its segmentation, from the 
primary bar ; here, in the Toad’s larva, the hyoid arch chondrifies only in that low part ; 
and for the remainder, above, we must look three months afterwards, some w 7 eeks subse- 
quent to the escape of the creature from the water. The articulation of this bar, which 
is properly the poster o-inferior segment, failing the front and upper part, or hyomandi- 
bular, articulates directly with the posterior face of the mandibular pier. I am now 
perfectly satisfied that this connexion of the hyoid with the mandibular arch is the only 
one that takes place during larval life. 
The form of the cerato-hyal at this stage (Plate 55. fig. 2, c.liy.) is oblong; it is 
curved externally and flattish within. Of the upper angles the anterior is rounded (as 
a condyle), and the posterior produced and leafy ; so are both the lower angles. 
Between the right and left bars there is a nodule of cartilage ( b.br .), which becomes the 
larger basibranchial behind, and the lesser basihyal in front. 
Besides the branchial arches there are two pairs of labials (upper and lower, u.l. & l.L). 
Thus, altogether, at this stage there are as chondrocranial elements already cartila- 
MDCCCLXXVI. 4 E 
