290 NERVOUS SYSTEM OF VERTEBRATES. 



ing centers going to make motor connections in the medulla 

 oblongata and spinal cord. The complexity of these decussations 

 is very great and the region is by no means well understood. For 

 attempts at the analysis of the midbrain decussations the student 

 must be referred to the papers by Edinger, Johnston, and Goldstein. 

 The great number of decussating fibers in this region is due to the 

 projection ventrad of the inferior lobes, which has crowded back 

 the decussations from the segment of the diencephalon. 



At the cephaHc border of the hypothalamus another collection 

 of decussating fibers is due in part to the same cause. These 

 constitute the postoptic decussations. The optic chiasma has 

 already been compared to the fibers of the lemniscus system in 

 the ventral decussation of the medulla oblongata. The postoptic 

 decussations are to be compared in a broad way with the other 

 elements of the ventral decussation. They belong chiefly to the 

 substantia reticularis, either of the hypothalamus or of the nuclei 

 in the colUcular region of the mesencephalon. These decussa- 

 tions have not yet been fully analyzed and the comparison of 

 those in fishes and mammals is especially difficult. For the most 

 recent treatment of these decussations the reader is referred to 

 the papers of Myers, Kappers, and Goldstein. In Petromyzon 

 the tractus lobo-epistriaticus, and in selachians the tractus olfacto- 

 hypothalamicus lateralis decussate in the postoptic region. 



DEMONSTRATION OR LABORATORY WORK. 



1. Study the general relations of the thalamus, hypothalamus, saccus 

 and nucleus habenulae in haematoxylin preparations of the brain of a 

 ganoid, bony fish or selachian, in the frog and in a mammal. 



2. Study the cells and fibers in the hypothalamus and nucleus hab- 

 enulae in a fish brain by the method of Golgi. Study the general 

 course of the chief fiber tracts in Weigert sections of the same brain. 



LITERATURE. 



Berkeley: The Nerve Elements of the Pituitary Gland. Johns Hopkins 

 Hospital Reports, Vol. 4. 1895. 



Bochenek, A.: Neue Beitrage zum Bau der Hypophysis cerebri bei 

 Amphibien. Bull, intemat. Akad. Sc. Cracovie. 1902. 



Boeke, J.: Die Bedeutung des Infundibulums in der Entwickelung der 

 Knochenfische. Anat. Anz., Bd. 20. 1901. 



