240 C. JUDSON HERRICK 



Gaupp ('99, p. 95) is also inclined to question the homology of 

 the parietal nerve of the frog with that described for reptiles. 



IV. THE FIBER TRACTS 

 1. The lemniscus systems 



The term lemniscus (or fillet or laqueus) was originally ap- 

 plied to certain sensory tracts of second or higher orders ter- 

 minating in the thalamus. In the interest of uniformity of 

 terminology there is a tendency among recent writers to enlarge 

 the concept to include all of the sensory tracts of this group. 

 Thus we have various spinal and bulbar lemniscus systems, 

 each of these tracts being defined by its functional connections. 

 The olfactory tracts are excluded, because they have no direct 

 connections with the thalamus proper; but the so-called optic 

 nerves should be included. 



In fishes these lemniscus systems connect primarily with 

 the tectum mesencephali, and the thalamic connections are for 

 the most part effected by tracts of a still higher order after a 

 synapse in the tectum (tecto-thalamic tracts). In the tailed 

 amphibians the tectakconnections are still the dominant features 

 of these systems, but some fibers of most of the lemniscus tracts 

 continue forward under the tectum to connect directly with 

 the thalamus, and the latter type of connection becomes in- 

 creasingly important in higher vertebrates. Accordingly, in 

 vertebrates in general, it is convenient to include with the 

 lemniscus tracts the tectal, as well as the thalamic fibers. 



In Necturus I have recognized the following members of 

 the lemniscus complex: (1) the optic lemniscus (tractus op- 

 ticus), (2) the spinal lemniscus (tractus spino-tectalis et thal- 

 amicus), (3) the acoustico-lateral lemniscus (fasciculus lateralis 

 of Mayser in fishes, lateral lemniscus of mammals), (4) tractus 

 bulbo-tectalis (of uncertain significance), (5) the visceral lem- 

 niscus (secondary vagus bundle of Mayser in fishes, ascending 

 visceral tract). These will next be described. 



