August 11, 1905.] 



SCIENCE. 



183 



In the selachians, its close association with 

 the main olfactory and its distribution within 

 the olfactory cup, might give ground for the 

 suggestion that it is a radix mesialis of the 

 olfactory nerve. This, however, appears to 

 me not well founded, since the nerve has no 

 ■connection, at any time of its growth, with 

 olfactory glomeruli. Even if it be one of the 

 olfactory bundles in an unusual position, its 

 method of origin, and difference from all other 

 olfactory radices would still justify the use of 

 the designation ' new nerve.' 



It is a relatively simple ganglionated nerve 

 that has apparently undergone little modifica- 

 tion. This, in itself, is a very notable cir- 

 cumstance, on account of its position on the 

 brain in a region of extreme modification. 

 Since it has remained in a relatively archaic 

 condition, we may conclude that its function 

 has not Been greatly elaborated. It may have 

 heen largely supplanted by the development 

 of the olfactory, or some of the branches of 

 the trigeminus. 



When all circumstances of its structure and 

 •development are taken into account, it seems 

 to me not unlikely that we have here the 

 remnant of a very ancient nerve, whose orig- 

 inal function is unknown, which in the proc- 

 ess of development has been reduced to sec- 

 ondary rank, through the prodigious develop- 

 ment of adjacent nerves and brain territories. 



It has been shown that this nerve precedes 

 the olfactory in embryonic origin, but the 

 assumption would not be justified on this 

 account, that it is, therefore, older in phylo- 

 genetic history, though such may be the case. 



Its development in so many adult selachians 

 would indicate that it is still functional, 

 though reduced to a subsidiary rank. 



Its ganglion will throw it among sensory 

 nerves. \ 



But, while it has a sensory moiety, some 

 considerations indicate that possibly it has 

 also a motor moiety. It has two roots, and 

 in the skate, both medullated and non-medul- 

 lated fibers have been observed in it. 



It will be extremely difiicult to determine 

 its physiological properties by experimenta- 

 tion. Its minuteness will render any manip- 



ulation or experimental study difiicult with- 

 out giving injury to the olfactory. 



It is doubtful if any trace of it be preserved 

 in higher vertebrates. Whatever its original 

 function may have been, it was in some way 

 superseded in the evolution of animal life, 

 and having first lost its importance, it there- 

 after disappeared. I have looked with espe- 

 cial care for it in a number of amphibians 

 and teleosts, and in the chick. Both embry- 

 onic and adult stages have been examined in 

 Necturus, Amhly stoma, the frog, the toad, the 

 trout, the catfish and the chick, but in none 

 of them has the nerve been found. 



From any point of view, it is ■ extremely 

 interesting that we have preserved so fully in 

 selachians and Dipnoi a ganglionated nerve 

 in front of the optic, bearing in its anatomy 

 testimony as to its ancient features, but of 

 which all traces have disappeared in higher 

 animals. 



Note. — Since the above was sent to the 

 printer the ' Nervus terminalis ' has been ob- 

 served in two rare selachians of ancient type 

 — Chlamydoselaclius and Mitsukurina. Pro- 

 fessor Burt G. Wilder noted its occurrence in 

 the former, photographed it, and, subsequently, 

 sent me a portion of the brain embracing the 

 nerve. In Chlamydoselachus it is similar in 

 position and anatomical features to the nerve 

 in Hexanchus. It is connected with the fore- 

 brain, within the median furrow, and upon 

 the terma about midway between the dorsal 

 and ventral surfaces. It runs directly to the 

 olfactory cup. Near the base of the cup it 

 has an enlargement which, upon microscopic 

 examination, proved to contain ganglion-cells. 

 As in Hexanchus, the main branch of the 

 nerve joins the median instead of the lateral 

 division of the olfactory fibers. 



Professor Wilder also generously sent for 

 my examination the anterior portion of the 

 brain of Mitsukurina. In that rare and costly 

 form the nerve is connected with the ventral 

 surface of the brain by two roots. It has a 

 very distinct ganglion lying on the olfactory 

 crus near the base of the bulbus. 



William K. Locy, 



