182 



SCIENCE. 



[K S. Vol. XXII. No. 554. 



branches passing to the median portion of the 

 cup. While the terminal twigs mingle inti- 

 mately with the olfactory fibers, they retain 



pocolf 



Fig. 5. Brain of adult ilustelus canis, from 

 above, and portion of the same from below, both 

 natural size. 



their independence and do not anastomose with 

 them. 



The dorsal attachment of the nerve to the 

 brain has been determined in eleven genera, 

 and sets aside the idea that it is usually, or 

 normally, connected with the ventral surface, 

 as has been suggested on account of its ventral 

 position in Amia, Ceratodus and Protopterus. 



As an illustration of the other type, having 

 a ventral attaclnnent with the brain, we may 

 take the brain of the common smooth hound 

 {Mustelus canis) of the Atlantic coast, which 

 is shown in Fig. 5. Here, the nerve emerges 

 from (or enters) the brain substance on the 

 ventral surface, about midway between the 

 anterior border of the prosencephalon and the 

 optic chiasma. It is interesting to note that, 

 in embryonic development, it first arises upon 

 the dorsal part of the primary fore-brain and 

 is carried to its ventral position through the 

 unequal growth of the brain-wall. The nerve 

 penetrates the brain substance, and, after 

 branching, terminates in the same region as in 

 the brain of Squalus acanthias. 



As shown in the figure, the nerve has two 

 ganglia — a distal and a proximal one — as is 

 the case with the ninth nerve. The peripheral 

 distribution of the fibers is similar to that in 

 Squalus acanthias. 



A few comments in reference to this nerve 

 may not be out of place. The only similar 

 nerve known outside the group of selachians 

 is in Amia, Protopterus and Ceratodus. In 

 the two former genera no ganglion was ob- 

 served by either AUis or Pinkus, but Sewert- 

 zoff, in 1902, noted a ganglion on this nerve 

 in embryonic stages of Ceratodus. The ven- 

 tral position of the nerve, close to the recessus 

 prceopticus in the three forms mentioned, led 

 Sewertzoff to propose for it the name of 

 ' Nervus prceopticus,' but its dorsal position 

 in so many selachians would make that name 

 inappropriate. Earlier (1899) I had sug- 

 gested in a tentative way the name ' accessory 

 olfactory' which is also objectional, as it 

 prejudices the question of its function. Since 

 this nerve arises on the morphological tip of 

 the primary fore-brain, and during some stage 

 of its existence is closely connected with the 

 lamina terminalis, I think the designation 

 ' Nervus terminalis ' will fit all cases and will 

 be a suitable name for it. 



Both its anatomy and embryology, as given 

 in my paper in the Anatomischer Anzeiger, 

 bring out its marked individuality and sepa- 

 rateness from other cranial nerves. This 

 would justify calling it a ' new nerve ' and, 

 therefore, giving it a new name. 



