6o6 "Journal of Comparative Neurology and Psychology. 



cyclostomes one would be inclined to expect that the sympathetic 

 ganglion related to the facial nerve in some fishes would be found 

 in process of separation from the facial ganglion proper, as Cole 

 thought was the case in Gadus (see discussion in Herrick 1900). 



4. The existence of peripheral ganglion cells in considerable 

 numbers and in the most diverse regions of the head. Retzius 

 (1890) has described subcutaneous ganglion cells in Myxine but, 

 judging from his figures, they do not resemble the cells described 

 here. Retzius cites Langerhans (1873) as dascribing subcu- 

 taneous ganglion cells in Petromyzon but I have not seen his 

 paper. 



5. The slightly differentiated condition of the maxillary and 

 mandibular nerves. The motor portion of the mandibular ramus 

 is clearly differentiated and supplies the muscles of the tongue, 

 which corresponds to the lower jaw. It is possible that the motor 

 trunk is accompanied by some sensory fibers for the covering of 

 the tongue, corresponding to the floor of the mouth in gnatho- 

 stomes, but they have not been found. The postorbital branches 

 to the skin may be assigned to the mandibular but they are far 

 removed from its motor portion. On the other hand, the maxil- 

 laris is largely motor. The muscles supplied by it, however, 

 probably have no counterpart in gnathostomes. If that is so, then 

 it is scarcely right to say that the motor fibers in the maxillaris 

 represent part of the mandibular trunk of gnathostomes. It is 

 simpler and truer to say that the cyclostomes present a peculiar 

 condition of the maxillaris due to the presence of the muscles of the 

 buccal funnel. Whether this be primitive or aberrant, it is the 

 most primitive condition which we know in craniates and in it 

 the trigeminus is indeed peculiar. It is the only nerve in cyclo- 

 stomes which appears to possess pre- and posttrematic rami. 

 The posttrematic ramus, however, is specialized motor and is 

 lacking in the cutaneous ( ?) and the branchial sensory and motor 

 components present in the branchial nerves. The absence of the 

 second and third is presumably due to the disappearance of the 

 hyomandibular gill sac. What is commonly called the pre-tre- 

 matic ramus is a great mixed nerve spreading fan-like to the skin 

 and musculature of the whole anterior part of the head in front 

 of the first gill sac, except the proper muscles of the tongue and 

 velum. This condition in cyclostomes throws a serious doubt on 

 the propriety of calling the maxillaris a pretrematic ramus in any 



