po Journal of Comparative Neurology. 



The mid-brain shows a layer of cells in the periphery, the 

 axis cylinders of which pass into the opticus, otherwise its struc- 

 ture is very much as that of the mid-brain of Amphibia. The 

 most important differences between the brain of Protopterus and 

 that of the lower vertebrates is found in the primitive fore-brain. 

 The roof of the diencepha'on, which entirely escaped the notice 

 of Fiillignet (no doubt by reason of the imperfect conservation 

 of his material) shows a complicated structure and forms a link 

 between the amphibian brain and that of the Selachii. Just in, 

 front of the post-commissure is found the epiphysis with a struc- 

 ture like that described by Ehlers for the Selachii ; its free end 

 is attached to the frontal bones by means of the arachnoid, and at 

 this point the cartilagenous skull sho«'s a perforation. That 

 portion described by Wiedersheim, Huxley and others as the 

 epiphysis, is in reality composed of three parts, namely : i, the 

 " Zirbelpolster " of Edinger; 2, the velum, which represents a 

 primitive form of the plexus choroideus medius ; 3, the cona- 

 rium (Adergeflechknoten of Goette), which may also be looked 

 upon as showing a primitive condition. The lower surface of 

 the diencephalon exhibits two small, yet always easily demon- 

 strable lobi inferiores [hypoaria]. The hypophysis is composed 

 of a glandular and nervous portion. 



The fore brain shows exceptional development. There 

 exists a posterior ventral portion, which according to its struc- 

 ture must be regarded as the lobus hippocampus. In it cells are 

 found which correspond in form to those found in the fascia 

 dentata of the iPiammalian brain ; fibres which connect them 

 with the lobi inferiores are also seen. In the entire pallium of 

 the fore brain, there exists a layer of ganglion cells which have 

 been separated from the central grey matter and lie in the white. 

 Another thin layer, found only in the anterior part of the fore- 

 brain, send fibres into the lobus [tuber?] olfactorius. Contrary 

 to the views of Fiillignet I must state that a lobus olfactorius 

 exists and is everywhere marked off from the other portions of 

 the brain, by a fissure. The nervous trunk which leaves this 

 lobe is, for a short distance, divided into a dorsal and a ventral 

 portion, only to unite again before it re ches the olfactory mem- 

 brane. Ventrad of the lobus olfactorius there is found a dis- 

 tinct elevation such as may be well seen in selachian brain ; for 



