324 H. W. NORMS AND SALLY P. HUGHES 



as in Squalus. Van Wijhe ('82) finds in stage L of the embryo of 

 Scyllium that the trigeminal nerve connects with the brain by 

 two roots, an anterior non-ganglionated part, which he regards 

 as belonging to the ramus ophthalmicus profundus, and a pos- 

 terior ganglionated root. Mitrophanow ('92) antagonizes the 

 views of van Wijhe, and while controverting the opinion that the 

 ophthalmicus profundus is an independent nerve asserts that in 

 Acanthias vulgaris the anterior trigeminal root [portio minor] 

 belongs with the maxillomandibular trunk, the ophthalmicus 

 profundus sending its fibers chiefly into the posterior root [portio 

 major]. Ewart ('89) states that in Laemargus the ramus oph- 

 thalmicus profundus arises by two to five rootlets immediately 

 in front of the main trigeminal root; but this is doubtless an error, 

 for the probability is that the relations that obtain in Squalus, 

 Scyllium, and Mustelus are typical. The discrepancy between 

 this account of the roots of the trigeminus in Squalus and the 

 description by Landacre is doubtless to be explained as due 

 largely to a later and more extensive development of motor fibers 

 in the stages studied by the writers. 



The ganglia of the two divisions of the trigeminal nerve are 

 sharply distinct in Squalus, both in embryo and adult. The pro- 

 fundus ganglion (gop.), wholly extracranial in position, is in 

 contact dorsally with the anterior (dorsal) lateral-line ganglion, 

 which sweeps out in a semicircle laterally, nearly hiding the 

 trigeminal ganglia (figs. 10, 11,- 16, 17, 21, 22, 24, 31, 32, 35, 51, 

 and 52). The profundus ganglion in the 'pup' stage is about 

 500m long and oval in shape. Its root fibers pass posteriorly at 

 the lateroventral border of the anterior portion of the lateral- 

 line ganglion, accompanied on its mesial border by fibers of the 

 ramus ophthalmicus superficialis trigemini (figs. 10, 11, 22, and 

 35, os.Vl). It is difficult to distinguish sharply between the 

 two nerves in the common mass which they form as they ap- 

 proach the brain, but as they pass toward the brain wall the 

 profundus fibers shift from a ventrolateral to a dorsomesial po- 

 sition (fig. 22). Reaching the anterior dorsal tip of the gasserian 

 ganglion, the profundus fibers pass through to enter largely if 

 not wholly the portio major, as described above, while the fibers 



