110 J. B. JOHNSTON 



ganglia on vomero-nasal branches of the olfactory nerve in Am- 

 blystoma serve to identify the nervus terminalis peripherally, 

 and show both that the nerve is ganglionated in urodeles and 

 that it has the same distribution as in reptiles and mammals. 



The evidence at present in hand seems to establish beyond 

 doubt the presence in all vertebrates of a receptive component 

 in the nervus terminalis supplying ectodermal territory. This 

 component is derived either from the terminal part of the neural 

 crest (Johnston '09 b, Belogolowy '12) or from the olfactory placode 

 (Brookover '10). The nerve is distributed to the nasal mucosa 

 or to a specialized part of it, the vomero-nasal organ. What is 

 needed now is definite knowledge of the central connections and 

 experimental evidence as to its function. 



One further suggestion, although very vague in its present form, 

 may be hazarded here. The close association of the nervus ter- 

 minalis with the vomero-nasal organ in amphibians, reptiles and 

 mammals suggests that the influence of this nerve in the fish- 

 like ancestors of these forms may have been an important factor 

 in the differentiation of the vomero-nasal organ. Also it may be 

 supposed that the distribution of the nervus terminalis in fishes 

 would give some indication as to the portion of the nasal sac 

 from which the vomero-nasal organ has been derived. 



SUMMARY 



In embryos of the turtle, pig, sheep and man there is found a 

 true nervus terminalis consisting of a ganglionated nerve whose 

 root enters the telencephalon caudal to the bulbus olfactorius. 



This nerve exists in addition to the nervus vomero-nasalis in 

 mammals, and the nervus terminalis is distributed chiefly to the 

 vomero-nasal organ. The olfactory fibers arising from the vo- 

 mero-nasal organ separate from the nervus terminalis to enter 

 the olfactory bulb. 



The nerve root enters the brain in the line of separation — zona 

 limitans — between the hippocampus above and the precommis- 

 sural body and tuberculum olfactorium below. 



In Amblystoma the nervus terminalis is ganglionated and sup- 

 plies the vomero-nasal organ as in reptiles and mammals. 



