NERVUS TERMINALIS IN AMIA 109 



Herrick ('09) says the nerve which he found in the frog in a 

 like position to the nervus terminalis in fishes is morphologically 

 similar so far as our information extends. DeVries ('05) went 

 farther and expressed himself as believing the nerve in fishes 

 homologous with the nerve to Jacobson's organ (organon vomero- 

 nasale) in higher vertebrates and to be looked for everywhere in 

 the vertebrate series. In reptiles Leydig ('97) found branching 

 cells in the " inter-epithelial gland" at the base of the columnar 

 epithelium of Jacobson's organ. Also in amphibians Rubaschkin 

 ('03) reports nerve cells in the olfactory bulbs sending fibers 

 peripherally into the nasal epithelium. We do not know what 

 relation these fibers bear to the glandular structures sometimes 

 found in the nasal capsule of amphibians. 



Although Jacobson's organ is not well understood physiologic- 

 ally, it is pretty clear that it is morphologically a part of the nose. 

 It develops as a cavity which evaginates from the nasal capsule, 

 and in the adult of some macrosmatic mammals has been found by 

 Miss Read ('08) to possess neurones similar to typical olfactory 

 neurones. She found these to end centrally in glomeruli of the 

 olfactory bulbs. Jacobson's organ has not been found as such in 

 the fishes, but the olfactory nerve is quite generally divided into 

 two rami peripherally, and this is true of some amphibians. It 

 seems to me probable that the nerve to the organon vomeronasale 

 is homologous with the median of the two rami in fishes rather 

 than with the nervus terminalis, as DeVries has suggested. The 

 nervus terminalis has generally been described as more intimately 

 connected with the median of the two rami of the olfactoy nerve 

 in fishes, and it may be that all, or a part only, of the nervus 

 terminalis component is included in the nerve to Jacobson's organ 

 in different species of higher vertebrates. In macrosmatic animals 

 a large number of olfactory fibers remain, while in other cases the 

 nerve to the organon vomeronasale may contain only the nervus 

 terminalis component. 



The condition of the nervus terminalis in sharks offers an 

 apparent exception to the statement made above that the nervus 

 terminalis of fishes is more intimately associated with the median 

 ramus of the olfactory nerve. The nerve in sharks is median, 



