THE EPIBRANCHIAL GANGLIA OF LEPIDOSTEUS 19 
root of this ganglion enters the medulla along with the remaining 
visceral roots of the X. One fibrillated nerve is present (truncus 
branchialis vagi lI). It arises from the anterior ventral end of the 
ganglion just behind its attachment to the placode and runs 
ventrally into the second true gill bar. 
The remainder of the visceral X is not differentiated into bran- 
chial ganglia. It is an elongated mass of cells lying somewhat 
ventrally and mesially to the lateralis X. Its posterior end as 
mentioned above is ill defined. Its middle portion is attached 
to the placode (placode 4) and one branchial nerve (truncus 
branchialis vagi II) arises from it just posterior to its attachment 
to the placode. This ganglionic mass differentiates later into 
the three remaining branchial ganglia of the X having the same 
composition as the first branchial of the X and consists of general 
visceral cells derived from the neural crest and special visceral 
or gustatory cells derived from the placodes. 
The root of this ganglion passes dorsally along with that of 
the first branchial ganglion and part of its fibers enter the medulla 
directly over the ganglion. Many of the fibers, however, at this 
stage pass further posterior forming a bundle lying near the 
medulla and enter the medulla posterior to the posterior end of. 
the ganglion. 
DETAILED DESCRIPTION OF THE EPIBRANCHIAL PLACODE OF 
THE VII IN THE 10 MM. EMBRYO 
This placode is completely detached from the epidermis in 
the 10 mm. embryo, as mentioned above. After describing it 
in this stage its later history will be followed first, and then the 
mode of origin will be taken up. 
After detachment from the epidermis, the placode occupies 
the anterior end of the general visceral ganglion of the VII nerve 
(fig. 1). The posterior and middle portions of the geniculate 
are round in transverse sections. The anterior third is indented 
on its mesial side by the ventro-lateral lateralis ganglion (figs. 
20, 21 and 27). The extreme anterior end varies a good deal 
in shape in different series owing to the varying relations of the 
