553 

this ganglion and enlarges, latero-caudal to the eapsule, into the Ggl. 
faciale s. genieuli which gives off two branches. One runs ventrally 
between the first visceral cleft and the A. carotis interna. The other 
passes dorsalward toward the proton of the columella. Here a fine 
strand, separating from the main branch, bends back, and running across 
the condensation, cannot be traced beyond the lateral end of the first 
cleft. The course of this strand identifies it as the chorda tympani. 
The main branch continues farther caudalward, where it terminates in 
one of the head myotomes. Ata short distance dorsal it to the region 
in which this branch gives off the chorda tympani, is found the small 
A. facialis and much farther dorsalward the broad V. capitis lateralis. 
The slightly older embryos, to which reference was made in the 
preceding paragraph, have a measurement of 6 and 7 mm. total body 
length. The parts of the 
skeleton are still very irregular- 
ly outlined, but a few impor- 
tant changes have occurred. 
As has alreadybeen mentioned, 
the connection between the 
dorsal and ventral hyoid 
regions is lost, and the proton 
of the columella has grown in 
toward the capsule. On can 
recognize its various parts; the 
base outlined in the capsule, 
the shaft lymg along the 
caudal wall of the first visceral 
eleft and the knob-like extra- Fig. 5. Embryo of 9 mm. total body 
columella forming the distal length. The section shows the general mor- 
. phological relations of the second stage of 
part of the condensation development. b.col. base of columella; 
(Fig. 4). As far as advance or  q. quadrate; s.col. shaft of columella. Other 
retardation in development is abbreviations the same as before. 
concerned, there is absolutely 
no difference between columella proper and extra-columella. A slight 
change has also taken place in the hyomandibular cleft. The ventral 
outpushing remains the same, but in the distal third of the dorsal 
portion the walls have grown together and closed the external opening. 
The epithelium lining the walls has not become obliterated but is 
still evident in the two bands closely pressed together. 

