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maxillo-mandibularis root joins the ganglion. The point of origin of 

 the ramus buccalis from the ganglion, and its relations to the points 

 of origin of the two apparent roots of the ganglion, seem to indicate 

 that all the fibres of the buccalis arise from the dorso-posterior root, 

 that root thus probably being the buccalis root of the complex ; and 

 as such I shall refer to it. A part of the fibres of the buccalis 

 might, nevertheless, be easily derived from the other, or maxillo- 

 mandibularis root of this part of the complex. 



The ramus ophthalmicus with its ganglion and root apparently 

 form, as will later appear, the bomologue of the Trigeminus I of 

 Koltzopf's (14) descriptions of Petromyzon. The remaining nerves 

 and roots of the complex apparently form the homologue of the 

 Trigeminus II of the same descriptions. 



Trigeminus I. 



A single large nerve trunk arises from the ophthalmicus, or 

 Trigeminus I, ganglion, the nerve having its origin from the anterior 

 end of the ganglion. This end of the ganglion lies approximately in 

 the transverse plane of the centre of the eye, that plane being also, 

 approximately, the transverse plane of what Aters and Jackson call the 

 anterior horn of the trabecula. The optic nerve, as it runs outward and 

 forward from its foramen to the eye-ball, passes across the anterior edge 

 of the floor of the trigemino-facialis chamber, there lying dorsal to the 

 cartilage that Ayers and Jackson describe as a short, thick, lateral 

 process that connects the trabecula with the palatine bar. The opticus 

 here passes close against the ventral surface of the base of the 

 ramus ophthalmicus, that nerve there still containing ganglion cells. 

 All the branches of the ophthalmicus thus lie definitely dorsal to the 

 opticus. 



The ramus ophthalmicus separates, immediately beyond its 

 ganglion, into two parts, one of which is the ophthalmicus trigemini 

 and the other a nerve that I take to be the homologue of the 

 ophthalmicus facialis of the gnathostome Ichthyopsida. This latter 

 nerve of Bdellostoma is the one that Müller describes, indifferently, 

 as the upper anterior cutaneous branch of the trigeminus, and as the 

 ramus cutaneus of the upper branch of the nervus trigeminus ; and it 

 is designated in his Fig. 3, PL 3, as 5'. As it is certainly not a 

 branch of the facialis, though probably the homologue of the ophthal- 

 micus facialis of the gnathostome Ichthyopsida, I shall call it the 

 ramus ophthalmicus lateralis n. Trigemini I. 



This ophthalmicus lateralis nerve of the adult Bdellostoma would 



