298 
which the two tubo-tympanic cavities open. 
THE DEVELOPMENT OF THE CHICK 
The median cham- 
ber communicates by a longitudinal slit (tubal fissure) in the 
Fig. 174. — A. Head of a chick embryo of 
4 days, halved by median section and 
viewed from the cut (After 
Moldenhauer.) 
B. Internal view of the pharynx of a 
pigeon embryo, corresponding in develop- 
ment to a chick of 10 days. (After Mol- 
denhauer. ) 
Col. 1., Colliculus lingualis. 
Colliculus palato-pharyngeus. 
surface. 
Col. p. p., 
Crea Crus 
inferior. Cr. s., Crus  superius.  Hyp., 
Hypophysis. Mx., Maxilla. N’ch., No- 
tochord. O. Ph. T., Ostium tubze phar- 
ynge. §. P., Seessell’s pocket. 2, 3, 4, 
Seeond, third, and fourth visceral arches. 
roof of the pharynx with the 
oral cavity (Figs. 168 and 
175). 
The frontal partition in 
question is a posterior pro- 
longation of the palatine 
processes of the maxillary 
arch, and forms as follows: 
If the head of a four-day 
chick be halved by a sagit- 
tal plane, and the interior 
of the pharynx and mouth 
‘avity be then viewed by 
reflected light, an elongated 
lobe will be seen on the me- 
dian surface of the mandib- 
ular arch and maxillary 
process (Fig. 174 A). This 
lobe begins far forward on 
the median surface of the 
maxillary process and may 
be followed posteriorly over 
the median surface of the 
mandibular arch to the first 
visceral pouch, where it 
ends with a free rounded 
extremity. The lobe itself 
is called by Moldenhauer 
the colliculus palato-phar- 
yngeus; it is bounded above 
and below by depressions, 
viz., the sulcus tubo-tym- 
the 
sulcus ventrally, 
both of which end behind 
panicus dorsally and 
lingualis 
in the first visceral pouch; 
anteriorly the ventral furrow disappears at the margin of the 
mouth, and the dorsal furrow near Seessel’s pocket. 
The maxil- 
