140 JOURNAL OF CoMPARATn'E NeUROI.OGY. 



ventricle; these afterwards join the main tract, mostly 

 uniting with its dorsal anterior portion. 2. The upper ones, 

 which pass through the geniculate body, and also join the 

 dorsal anterior portion of the optic tract. 3. The upper 

 fibres. These do not terminate in the thalamus, but may 

 possibly, as in the lower vertebrates, have some connection 

 with this grey substance through which they pass. In close 

 proximity to the tract are peduncular fibres, other fibres that 

 form the inferior commissure, and fibres of the subthalamic 

 posterior decussation, corresponding, perhaps to the fibrse 

 ansulatae of the lower vertebrates. The correspondence is a 

 true one, no doubt, for, according to Bellonci's description, 

 and also according to the figures of the various types, the 

 position of this decussation, as well as the terminal arrange- 

 ment of the fibres composing it, are similar to those of the 

 fibras ansulatne. There are also thick medullary fibres which, 

 forming a network, cross inside of the inferior commissure 

 and the decussation; and in addition to all these there is a 

 thick bundle of medullary fibres which comes from the 

 interior of the optic lobes and goes to the central nidulus of 

 the thalamus. 



It is Bellonci's opinion ['", p. 19] that some of the optic 

 fibres in the mammalian brain never crosses either in the 

 chiasma or in the subthalamic substance, and this, he says, is 

 more easily seen in the rodents than in any other of the 

 mammalian types. Some fibres that do not cross at the 

 chiasma, do so in the tuber cinereum, and then join the optic 

 tract. In the region of the chiasma the following kinds of 

 fibres are associated with the optic ones: the inferior com- 

 missure, the inferior fibrae ansulatae, of which he mentions 

 three groups: the first goes caudad and dorsad inside of the 

 thalamus; the second goes towards the optic tract, some of 

 the fibres running just outside of the tract finally enter the 

 occipital lobe; the third goes vertically dorsad and loses 

 itself in the corona radiata, the medial thalamus fibres that 

 pass from various portions of the thalamus to the dorsal part 



