NERVUS TERMINALIS IN AMIA 53 



the human embryo the olfactory nerve arises exclusively from 

 the periphery. The view prevails at present that the olfactory 

 nerve differs from all other nerves in vertebrates in that its cells 

 arise and remain in the ectoderm. Bedford's investigations on 

 embryo swine support this view. 



It would seem from the brief account just given that the em- 

 bryology of the olfactory nerve is simple, but Mimes Marshall, 

 Balfour, von Kolliker, Beard, Chiarugi, Disse, and others have 

 described a ganglion in the developing olfactory nerve. Some 

 thought this ganglion came from the brain or from the forward 

 continuation of the neural crest into the region of the olfactory 

 nerve. His ('89) described the ganglion as coming from the 

 periphery and contributing neuroblasts to the formation of the 

 olfactory nerve. Disse ('96) says that the cells of the ganglion 

 give rise to the sheath cells of the olfactory nerve. Bedford did 

 not determine their fate in swine. 



In 1895 Pinkus described a new nerve in Protopterus, which 

 is intimately associated with the olfactory nerve. Soon after- 

 ward Allis ('97) found a nerve in Amia calva near the olfactory 

 nerve. He noted its ganglion in the young and homologized 

 the nerve with Pinkus' nerve in Protopterus. About two years 

 later Locy ('99) found a nerve in sharks related peripherally 

 with the olfactory mucosa. As it had a more dorsal connection 

 with the brain than that described by Pinkus for Protopterus, he 

 was not inclined to homologize the nerve in selachians with the 

 one in Protopterus. He extended his observations to other sharks 

 and found in some species a more ventral connection of the nerve 

 with the brain. He then thought the nerve homologous in 

 Protopterus, Amia and selachians ('03). When the nerve was 

 found to be present in a large number of sharks Locy ('05) 

 named it the nervus terminalis. He also treated this nerve as a 

 part of the olfactory nerve when he first described its develop- 

 ment in Squalus acanthias ('99), but later ('05) he came to con- 

 sider it as an independent nerve. 



Bing and Burckhardt ('04) described the nervus terminalis in 

 adult Ceratodus where Sewertzoff ('02) had previously seen it in 

 embryos. In all probability it has not been sufficiently sought 



