CRANIAL NERVES OF SIREN LACERTINA 321 
over the extreme posterior dorsal tip of ceratobranchial 2. One 
of these two branches, of communis and motor fibers (X.2 pst.), 
running antero-ventrally along the lateral border of ceratobran- 
chial 3 as the ramus posttrematicus, gives off a branch (dbr.3) to 
the depressor muscle of the third gill and communis (and possi- 
bly general cutaneous) fibers to the same gill. The other branch 
(br.2,X.2) of motor, general cutaneous and communis fibers, 
supplies the levator muscle of the second gill (lbr.2) and the re- 
gion of the second (and third?) gill. It also sends an anastomos- 
-ing branch to the main sensory nerve of the second gill. The 
second division (br.3,X.2) of the dorsal portion of the third branch- 
ial nerve, composed of motor, general cutaneous and communis 
fibers, passes posteriorly between the levator arcus branchialis 3 
and levator arcus branchialis 4 muscles, gives off a branch to the 
levator muscle of the third branchial arch (lab.3), divides into 
two parts and curves laterally over the top of the third cerato- 
branchial a little posterior to the first division of the nerve. Of 
its two parts, the one more ventral ( lbr.3), of motor and general 
cutaneous fibers, supplies the levator muscle of the third gill and 
sends general cutaneous fibers to the same gill. The nerve for the 
depressor branchialis 3 muscle sometimes comes from this branch. 
The second more dorsal part of general cutaneous and communis 
fibers supplies the third gill. After giving off the branch to the 
depressor branchialis 3 muscle, the ramus posttrematicus of the 
third branchial nerve consists of communis fibers only. It 
passes along the lateral border of the third ceratobranchial arch 
to about the ventral fourth of its length and then shifts dorsally 
around to the median side of the arch, where it supplies the mucous 
epithelium of the arch, apparently replacing functionally the 
ramus pretrematicus of the dorsal part of the arch. 
The ramus pharyngeus of the third branchial nerve (X.2,ph.) 
divides into three parts: a pharyngeal branch to the dorsal 
pharynx wall; a ramus pretrematicus (X.2,prt.) which curves 
over the dorso-lateral extension of the pharyngeal cavity to the 
medial border of the second branchial arch, dividing into a 
number of small branches while in that position; a ramus pretre- 
maticus (X.3,prt.) which passes back, dorsally and laterally, in a 
