MORPHOLOGY OF THE VERTEBRATE OLFACTORY ORGAN. 315 



nerves, and are in no way intermediate between the dogfish 

 and such Sauropsida as I have examined. Finally, the 

 Teleosteans, if the salmon and trout may be taken as typical 

 of that group, while they resemble the Amphibia in the 

 extreme shortness of their olfactory nerves in the early stages 

 of development, seem to differ somewhat from the -other 

 types in the exceedingly late appearance of the olfactory 

 lobes, and in the striking resemblance in general anatomical 

 behaviour between the olfactory and the other cranial 

 nerves. 



The nomenclature of the olfactory nerve is, unfortunately, 

 somewhat overburdened with synonyms, a never-failing 

 source of confusion and inaccuracy. The " olfactory nerve " 

 of an adult vertebrate is, })erhaps, best described as con- 

 sisting of three pans; a ])roximal tractus olfactorius arising 

 from the cerebral hemisphere, an intermediate ganglionic 

 enlargement or bulbus olfactorius, from whose distal extremity 

 the third part or tiervus olfactorius arises.^ Of these parts 

 the two former are commonly and correctly described as 

 being properly parts of the brain, and as togetner con- ' 

 stituting the rhinencephalon. By some authors, however, 

 the term rliinencephalon appears to be limited to the bulbus 

 olfactorius, the tractus olfactorius being then sooken of as 

 the rhinenccphalic crus.^ By olfactory lobe or olfactory 

 vesicle is usually meant the hollow diverticulum of the fore- 

 brain or cerebral hemisphere in the embryo, from which both 

 the tractus olfactorius and bulbus olfactorius of the adult are 

 developed, and which has hitherto been erroneously sup- 

 posed to be the earliest part of the " olfactory nerve " to be 

 developed. It would, perhaps, be well to limit the term 

 olfactory lobe to this embryonic structure ; Owen employs it 

 in the adult as synonymous with bulbus olfactorius. 



From the descriptions I have already given it follows that 

 the nervus olfactoritis is the earliest of the three elements 

 to be developed, and that it alone is the direct homologueof 

 the other cranial nerves. The term olfactory nerve ought 

 then to be strictly limited to the nervus olfactorius. Since, 

 however, there is considerable inconvenience in disturbing 

 established nomenclatures, it may ])erhaps be well to con- 

 tinue to use the term olfactory nerve in the ordinary ana- 

 tomical sense, and to confine oneself to the term nervus 



' Vide Max ScbiiUze. "UiitersuchunEjen iiber den Bau der Nasensch- 

 leimhaut bei dem Menscben und Wirbeltbiere." Halle, 1862, pp. 18, 19; 

 and Stannius, ' Haudbucb der Auatomie der Wirbeltbiere,' 2 Aufiage, 

 1854, p. 165, seq. 



' Owen, ' Anatomy of Vertebrates,' vol i, p. 283, 1866. 



