Hekkick, Morphology of Brain of Bony Fishes. 245 



/"'/V. 1. Section at the union of the olfactoria with the ihinaHc 

 aspect of the hemispheres. Op. n., optic nerve. 



Pig. ,'• Section somewhat caudad of the abo\'e. Lat. /., lateral 

 lobe; Mesa. /., mesaxial lobe; F. r/iiii., rhinalis fissure. 



Fig: .j. Section cephalad of the decussation of the optic nerves. 

 The cerebrum is here overarched by the mesencephalon and the volvula. 

 Hip. /., hippocampal lobe; tolx'., volvula cerebelli. 



Fig: 4. Section at the decussation of the optic nerves. Torus 

 lono-..^ torus longitudinalis; JMcinbr. fccf., the tela tecti or membranous 

 portion of the tectum opticum. 



Fig. .'). Section through the pnethalamus, //v. ///. 



Fig. >;. Section through the mid-thalamus. //., habena. 



Fig. 7. Section cephalad to hjpoaria. J/. l>., Meynert's bundle. 



Fig: S. Section through post-thalmus. 



Fig: 9. Section at the caudal level of the hypoaria. Region of 

 mesencephalic decussations. A(/. S., aqueduct of Sylvius. 



Fig-. 10. Section at the beginning of the cerebellum. 



Figs. 11-l.i, Successive sections through the medulla and cere- 

 bellum. Description will be deferred to subsequent installment. 



PLATE XXI. 



Figs. 1-3. Sections through tlie medulla of the black-horse, con- 

 tinuing the series of Plate XX. J J), trig-cm.., trigeminal lobe; /.. vagi, 

 vagal lobes or tubers. Details will be given in later installment. 



Figs. 4.-0. Transections through the olfactory crura and cerebrum. 



Fig. 4 is some distance cephalad of Fig. 5, and on the opposite (left) 



side. 



Figs. 7-l()- Transections of the brain of Dorosoiiia. 



Fig. 7. Section at the anterior commissure. 



Fig. S. Section at the superior commissure. 



Fig. 9. Section at the exit of the third nerve. 



Fig. 10. Section at the caudal level of the optic lobes to illustrate 

 the great induplication of the cerebellum along the median (line at a). 

 The suppressed lateral ventricle, or recessus lateralis, with its mem- 

 branous lateral walls is indicated at z'ciitr. lat. cerebel. 



