242 C. JUDSON HERRICK 



In Necturus I have found these three parts of the optic tract 

 substantially as described by Wlassak, though all are unmye- 

 linated both before and after their decussation. The axial 

 bundle is composed of coarser unmyelinated fibers than the 

 others and in the nerve immediately distally of the chiasma 

 these fibers occupy the dorsal part of the cross section. Upon 

 entering the brain they turn sharply caudad and dorsad (figs. 

 1, 15 to 19, 25, 65 tr.op.ax.) and decussate in the dorso-rostral 

 part of the chiasma ridge. Immediately after their decussa- 

 tion these fibers spread out and pass dorsad and caudad through- 

 out the deeper parts of the stratum album above the chiasma 

 ridge, some of them penetrating the lateral forebrain tract 

 (figs. 1, 18, 19, 65, tr.op.ax.x.). They can be followed as far 

 dorsally as the sulcus ventralis thalami; beyond this level they 

 are so scattered that it is impossible to distinguish them from 

 the fibers of the postoptic commissure with which they are 

 mingled (see further, p. 244). 



The basal bundle of the optic tract is of considerable size; 

 its fibers decussate in the ventral part of the chiasma ridge 

 in company with those of the marginal bundle. After their 

 crossing they turn abruptly caudad and dorsad along the ex- 

 treme lateral surface of the hypothalamus and end on the ven- 

 tro-lateral surface of the cerebral peduncle among the dendrites 

 of the neurons of the cerebral peduncle rostrally of the nucleus 

 of the III nerve. These dendrites pass to the lateral surface 

 of the brain and then forward and participate in the formation 

 of a dense neuropil which I term the area lateralis tegmenti. 

 The contorted fibers of the basal optic tract end freely in this 

 dense neuropil. They do not extend farther caudad than the 

 level of the III nerve (figs. 52 to 55, 65, tr.op.b.). I find this 

 area of neuropil in larval Amblystoma and within it free ter- 

 minals of fibers derived from the chiasma ridge. In these 

 larvae also I have observed free endings of fibers of similar 

 appearance coming into the same neuropil from behind, prob- 

 ably fibers of the ascending visceral tract (p. 250, cf. also p. 295). 



The fibers here designated as basal optic tract undoubtedly 

 correspond with the 'basal optic bundle' of Wlassak's account 



