288 C. JUDSON HERRICK 



enter the tractus thalamo-peduncularis dorsalis for the cerebral 

 peduncle (p. 264) and the tractus dorso-ventralis thalami for 

 the pars ventralis thalami (p. 266); but the larger part enter 

 the tractus thalamo-frontalis anterior. These are mostly very 

 fine unmyelinated fibers which are gathered into several very 

 compact fascicles which descend abruptly ventralward, at the 

 same time curving shghtly caudalward, to enter the lateral 

 forebrain bundle and then turn forward to end in the lateral 

 wall of the cerebral hemisphere (p. 268). A few scattered 

 mj^elinated fibers are found among these fascicles, and from the 

 caudal end of the pars dorsaUs thalami there are more of these 

 myelinated fibers (tractus thalamo-frontalis posterior). 



The caudal part of the pars dorsalis thalami lying ventrally 

 of the pars intercalaris diencephali receives chiefly the thalamic 

 terminals of the spinal and acoustico-lateral lemnisci. Its 

 efferent fibers are in part directed backward and downw^ard 

 to the cerebral peduncle in the tractus thalamo-peduncularis 

 dorsalis, and in smaller part downward and then forward to 

 enter the tractus thalamo-frontalis posterior, as just mentioned. 



The pars dorsalis thalami is the great somatic sensory re- 

 ceptive center of the diencephalon. Its fiber connections show 

 that in Necturus it is concerned chiefly with intrinsic thalamic 

 reflexes of a very primitive sort, the efferent pathways for these 

 responses being short axons discharging into the pars ventrahs 

 thalami and cerebral peduncle. In addition to these connec- 

 tions, there is a small but clearly defined thalamo-frontal path 

 discharging into the lateral wall of the cerebral hemisphere and 

 probably concerned with correlations of a higher order. These 

 tracts are the precursors of the sensory thalamic radiations of 

 mammals. The differentiation of specific functional areas in 

 the pars dorsalis has begun, but has advanced only a very short 

 distance in the direction of the mammalian conditions. It is 

 probable that its functional character resembles most closely 

 that of the medial nucleus of higher forms. The lateral and 

 ventral nuclei are, however, represented, though not spatially 

 separate. The pars optica seems to be concerned wholly with 

 the intrinsic thalamic reflexes ; it cannot, therefore, be compared 



