NERVUS TERMINALIS: MAMMALS 5 



ion and concluded that the nerve of selachians is homologous with 

 that described by Pinkus in Protopterus and later by AUis in 

 Amia. The same author in his paper of 1905, based on the ex- 

 amination of twenty-seven species of adult selachians and the 

 embryological history of the nerve in Squalus, proposed the name 

 of 'nervus terminalis' for this new nerve. This name has been 

 generally adopted. 



In the interval Sewertzoff ('02) had described the nerve in 

 embryos of Ceratodus, finding it ganglionated and terminating 

 peripherally in the mucous membrane of the anterior nasal 

 chamber — not in the sensory epithelium. On account of its 

 point of central connection with the brain he suggested for it 

 the name of 'nervus praeopticus.' This nerve had also been 

 cited in the adult of Ceratodus by K. Fiirbringer in 1904, as 

 well as by Bing and Burckhardt in 1904 and 1905. 



Conditions in the different classes of vertebrates. Since 1905 a 

 considerable literature has accumulated regarding the nervus 

 terminaHs. Its presence. has been demonstrated in all cases of 

 vertebrates except the cyclostomes (and possibly the birds) 

 and various suggestions regarding its function have been made 

 from time to time. 



Inasmuch as the present paper deals with the nervus terminalis 

 chiefly in mammals, it is not necessary to enter into a review of 

 the rather extensive literature of the nerve in the lower verte- 

 brates. But, since the nerve presents some modifications and 

 some differences in the mammals, it is advantageous both for 

 comparison and for discussion of results, to have a brief state- 

 ment of the chief structural features which have been observed 

 in other classes of the phylum. The nervus terminalis appears 

 to be more generalized in the fishes, especially in the selachians, 

 and in discussing its relations in mammals it would be a mistake 

 to disregard the findings in the lower vertebrates. 



Fishes: a) Selachians. In a paper on the telencephalon of the 

 selachians, Johnston ('11) shows that typically the nervus ter- 

 minalis enters the brain substance near the recessus neuroporicus 

 internus. He remarks: "Some evidence has appeared recently 

 (Burckhardt, '07, p. 340; Brookover, '10) that the nervus ter- 



