MIDBRAIN AND THALAMUS OF NECTURUS 267 



21. The basal forebrain bundle 



The basal forebrain bundle of Amphibia was described by 

 Osborn ('88, p. 78) as containing both ascending and descend- 

 ing fibers relating the cerebral heinisphere mth lower regions 

 as far back as the spinal cord. This was confirmed by Van 

 Gehuchten ('97, p. 53) on the basis of Golgi preparations of 

 Salamandra. It seems probable that the complicated connec- 

 tions of the fibers of this bundle as described by Van Gehuchten 

 represent, not the course of a single tract, but the confusion of 

 several distinct fiber systems no one of which extends through 

 the entire length of the brain. Recent authors have separated 

 the basal forebrain bundle into two parts, a lateral forebrain 

 bundle related to the lateral wall of the cerebral hemisphere, 

 and a medial forebrain bundle related to the medial wall. Each 

 of these bundles is a complex containing both ascending and de- 

 scending fibers, whose analysis has not yet been completely 

 effected. 



1) The lateral forebrain bundle (fasciculus lateralis telen- 

 cephali). This is the most compact and obvious fasciculus in 

 the brain of Necturus. Its course through the ventro-lateral 

 wall of the telencephalon has been figured by Kingsbury ('95, 

 figs. 28 to 31), McKibben ('11, figs. 9 to 18), and Rothig ('H, 

 figs. 5 to 15). In this contribution it is illustrated in figures 

 1 to 11, 15 to 20, 25, 28, 43, 46, 49, 55, 57, 68, {f.lat.L). It 

 contains both myelinated and unmyelinated fibers of several 

 sorts, some of which will next be enumerated. 



Tr actus strio-thalamicus et tegmentalis. These fibers descend 

 from the ventro-lateral area of the cerebral hemisphere (pri- 

 mordial corpus striatum) and are strongly myelinated, at least 

 in part. At the transverse level of the postoptic commis- 

 sure they begin to scatter (figs. 3 to 6, 19, 20, 55, 57, f.lat.t.) 

 and many of them end in the adjacent pars ventralis thai- 

 ami {tractus strio-thalamicus, fig. 57, tr.st.th.). The remainder 

 turn dorsalward and enter the cerebral peduncle, where they 

 join the bundles of motor fibers in the tegmentum {tractus 

 strio-tegmentalis, figs. 55, 57, tr.st.t.). Their lower termination 



