Pb:mherton, Structure of tJic Optic Thalanii. 137 



peduncles, as shown in the transverse section of the thahimi, 

 is made up of the prosencephalic sensory tracts formed 

 by the mesencephalon and the diencephalon. The basal 

 prosencephalic tract passes from the medulla into the basal 

 portion of the prosencephalon. Some fibres terminate im- 

 mediately below the anterior commissure, others enter the 

 corpus striatum. He also says that the bundles of fibres 

 coming from the lateral regions of the medulla and spreading 

 over the mesencephalon, in the same manner spread over the 

 diencephalon. The connection is a well-known one. As far 

 back as 1875, Stieda ['p. 396] showed that in the case of the 

 turtle, the fibre-bundle coming from the mesencephalon is 

 joined by the bundle from the thalamus and continues into 

 the prosencephalon. Stieda ['■' p. 395] also says that in the 

 reptiles the nerve-fibres of the thalamencephalon are for the 

 most part the continuations of the peduncle, both of the 

 lateral and of the central tracts. Some fibres come from the 

 mesencephalon, and other fibres joining these, pass to the 

 prosencephalon; and some from the mesencephalon cannot be 

 traced further, and probably terminate in the thalamus. This 

 is, of course, the basal prosencephalic tract to which Stieda 

 referred, and is exactly like the course of the fibres in the 

 amphibian brain. 



In birds, the tract in which all the fibres join, descend 

 cephalad to the anterior commissure, to the base of the cere- 

 brum; it passes this at the front edge of the optic tract (of 

 the same side), goes around the crus, bending laterad, and 

 terminates between the posterior dorsal edge of the thalamus 

 and the optic lobe. 



Edinger shows ['' see Fig. 64, p. 79,] us that in the 

 human brain the fibres passing from the anterior peduncle of 

 the cerebellum, and running just under the corpora quadrige- 

 mina, enter the " red nucleus," after decussating, and thence 

 send fibres to the thalamus, to the internal capsule, and to the 

 tegmentum. The fibres passing just above the pons, 

 go into the thalamus, and from there run dorsad in radiating 



