MORPHOLOGY OF THE FOREBRAIN 433 



part of the preoptic nucleus. I find the same relations in the 

 frog. 



The pars ventro-lateralis of the hemisphere contains elements 

 which give rise to the corpus striatum of mammals. From it 

 (and probably also from the pars dorso-lateralis) fibers arise which 

 terminate in the pars ventralis thalami. This component of the 

 lateral forebrain tract is the tractus strio-thalamicus, which par- 

 tially decussates in the anterior commissure. Its fibers, which 

 are partly medullated, terminate chiefly at the transverse level 

 of the post-optic commissure, though some continue farther cau- 

 dad. In the caudal part of the pars ventralis thalami they are 

 joined by many other medullated fibers from this part to form 

 the tractus thalamo-bulbaris et spinalis, and by the tractus mam- 

 millo-bulbaris from the hypothalamus. These fibers enter the 

 strong ventro-lateral descending tract of the midbrain and ob- 

 longata. The tractus tecto-spinalis is added in the midbrain 

 and the whole system evidently corresponds with the descending 

 pedunculus cerebri tracts of mammals. From this it follows that 

 the ventral part of the hemisphere and the ventral part of the 

 thalamus are of common type, both being fundamentally centers 

 of efferent discharge and the correlations directly connected there- 

 with. 



The great lemniscus system of the medulla oblongata passes 

 forward into the dorsal part of the midbrain, i.e., above the sul- 

 cus limitans, where the larger part of its fibers terminate in the 

 tectum mesencephali (primordial colliculus inferior). This por- 

 tion of the lemniscus of Necturus is shown in Kingsbury's figures 

 ('95). Some of its fibers, however, continue upward to end far- 

 ther forward in the tectum and in the pars dorsalis thalami. 

 These are joined by other fibers from the tectum mesencephali 

 to the thalamus. A strong medullated tract associated with the 

 rostral end of the lemniscus passes from the tectum mesencephali 

 through the lateral part of the thalamus to enter the post-optic 

 commissure. Other similar fibers enter this commissure from 

 nearly all portions of the pars dorsalis thalami. 



A large collection of medullated and unmedullated fibers passes 

 from the rostral end of the pars dorsalis thalami to the grey nuclei 



