DEVELOPMENT OF THE SKULL IN THE BATRAOHIA. 
17 
that the fore brain is turned downwards and somewhat backwards, and the mid brain 
is tilted upwards and forwards, and forms the actual end of the embryo, lying against 
what is called the “ frontal wall. 
The fore and hind vesicles are thus brought into contiguity, and the organic apex, 
or real fore end of the embryo, is a little in front of the hind vesicle ; it looks down¬ 
wards and a little backwards. 
At that point a remarkable process takes place ; the notochord turns downwards, 
taking, as the skeletal axis, the same direction as the neural axis; the fore brain after 
a time sends a budding process out, and the oral mucous membrane sends a budding 
process in, and the two, gradually becoming mutually engrafted, the one upon the 
other, open freely into each other, and then the lower process becoming closed below, 
we have the pituitary body formed. 
In this quasi-archaic condition of the head and its parts, the body is a mere 
appendage, solid hyaline cartilage forms first where most pressure is, and the paraxial 
bands grow first of all from near the apex of the notochord to near the frontal wall. 
But the fore brain swells and hangs down ; the skeletal parts respond to this 
condition and wind their way round its base, embracing its sides, and then meet, or 
nearly so, in front, to diverge again in the nasal region of the face. 
After a few days the paired bands have developed backwards under the hind brain 
(ibid., figs. 3 and 4), and behind the head they appear in patches that alternate with 
the somatomes (muscle-segments, &c.) along the spinal region. 
Then, in Tadpoles Jive-twelfths of an inch long (op. cit., Plate 55, fig. 3), the 
chondrocranium is simply a pair of planks on which the brain lies ; it has become 
much straighter, but the mid brain lies high, still. 
Strength, however, has been gained by fusion at two points (in the antorbital and 
postorbital regions), and between these two points the bars are becoming cre-sted; 
these ridges are the beginning of the ethmoidal and sphenoidal side walls. 
Returning to the earliest stage we find that there are, indeed, two pairs of cartilage 
on each side nearly equal, with a third pair of much shorter bars. 
In these temporary sucldng fishes the chief parts of the organism are all crowded into 
the head and throat; all else is their paddling fin, and the creature is called a bull¬ 
head, on account of this cephalic preponderance. 
The second, more external, cartilaginous band (pd., q.), carrying at its end a short 
inturned segment (Mk.), is the “pier” of the mandible, with its free swinging joint, 
the rudiment of the lower jaw. 
Under that pier, one-fourth of the way from its distal end, the third cartilage is 
seen (c.hy.) ; this is the free joint of the hyoid ( lingual) arch whose pier or epi-hyal 
element does not appear for three or four months to come, and when developed is 
devoted to new purposes, does not become the practical “ suspensorium ” of the lingual 
arch at all, but forms part of the outworks of the auditory labyrinth. 
* See Balfour’s ‘ Elasmobranclis,’ plate 7. 
MDCCCLXXXI. 
D 
