146 
buccalis in Petromyzon but in this genus the nerve apparently differs 
from that in Geotria in that it consists of lateralis fibres only. In 
addition to the two nerves just mentioned and which I can more or 
less identify from JoHNSToN’s reconstructed figure, there exist the 
two large nerves (Q1 and Q2) of which I cannot find the repre- 
sentatives in any published figure of Petromyzon facial nerves. The 
upper nerve (Q1) apparently?) arises from the brain considerably 
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Fig. 30 (x cire. 1), shows distribution of facial nerves of Geotria australis, as 
seen after removal of skin from side of head. 
Fig. 31 (x cire. 2). Ventral view of head region of Mordacia mordax. 
Fig. 35 (x 2). Semi-diagrammatic transverse section (about 2 mm. thick) 
through the head of the Velasia stage of Geotria at the level of the anterior end of 
the piston cartilage (see Appendix). 
Fig. 36 (X 2). Semi-diagrammatic transverse section (about 2 mm. thick) 
through the Velasia head at the level of the most anterior segment of the dorsal 
myotomes (see Appendix). 
Fig. 37 (x 2). Semi-diagrammatic transverse section (about 3 mm. thick) 
through the Velasia head at the level of the hind end of the auditory capsules 
(see Appendix). 
1) The brain was in a very poor state of preservation. 
