CHAPTER XX 

 THE SYSTEMS OF FIBERS 



THE principles of classification and nomenclature of nerve fibers 

 here employed are explained on page 9. A systematic account 

 of them is very difficult because of their dispersed arrangement, 

 their many deviations from the familiar mammalian pattern, and a 

 cumbersome and confused nomenclature; yet gratifying success has 

 attended efforts to resolve the amphibian tissue and discover mam- 

 malian homologies or their primordia. It is not our purpose in this 

 chapter to give a comprehensive list of the tracts of Amblystoma 

 that have been identified and named. References are given to the 

 literature in which incomplete lists have been published and to pages 

 of this book where particular systems of fibers are described. To these 

 there are added descriptions of a few other systems of fibers of special 

 importance and complexity. 



Lists of tracts of Necturus have been published for the medulla 

 oblongata ('14rt, '30), midbrain and thalamus ('17), and forebrain 

 ('336). At the end of the latter paper is an alphabetical list of abbre- 

 viations which includes many tracts, with references to previous de- 

 scriptions and synonyms. For Amblystoma a similar list of abbrevia- 

 tions ('36, pp. 309-12) includes many tracts of the cerebral peduncle, 

 with page references to the text. Other lists of tracts of Amblystoma 

 have been published ('27, '36, '39, '396, '42), and Bindewald ('14) 

 gave in tabular form a useful summary of previous descriptions of the 

 parts of the amphibian forebrain and related fiber tracts, with 

 homologies. The tracts of several species of urodeles have been de- 

 scribed in the literature cited on page 11. The following systems of 

 fibers of Amblystoma have been more or less completely described: 

 peripheral nerves (Coghill, '02), olfactory tracts ('27, p. 282; Binde- 

 wald, '14; compare Necturus, '336, p. 124, '346), optic tracts and 

 tectal connections ('25, '41, '42; compare Necturus, '41a), postoptic 

 (supra-optic) commissures ('42, p. 219; Necturus, '41a, p. 513), the 

 visceral-gustatory system ('44a, '446), cerebellum (Larsell, '20, '32), 

 tegmental fascicles ('36). 



In this work under appropriate headings there are lists of tracts 



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