298 



THE DEVELOPMENT OF THE CHICK 



which the two tubo-tympanic cavities open. The median cham- 

 ber communicates by a longitudinal slit (tubal fissure) in the 



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 

 cavity 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 

 o.Ph.T- [■'" "-'•' '• :i'M -.. ■jS^^^'^Cri be followed posteriorly over 



the median surface of the 

 mandibular arch to the first 

 visceral pouch, where it 

 ends with a free rounded 



CoV.pf. 



Fig. 174. — A. Head of a chick embryo of 

 4 days, halved by median section and 

 viewed from the cut surface. (After extremity. The lobe itselt 



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., CoUiculus linguaHs. Col. p. p., 

 Colliculus palato-pharyngeus. Cr. i., Crus 

 inferior. Cr. s., Crus superius. Hyp., 

 Hypophysis. Mx., Maxilla. N'ch., No- 

 tochord. O. Ph. T., Ostium tuba? phar- 

 yngae. S. P., Seessell's pocket. 2, 3, 4, 

 Second, third, and fourth visceral arches. 



IS called by Moldenhauer 

 the colliculus palato-phar- 

 yngeus ; it is bounded above 

 and below by depressions, 

 viz., the sulcus tubo-tym- 

 panicus dorsall}^ and the 

 sulcus lingualis ventrally, 

 both of which end behind 



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- 



