NERVOUS SYSTEM. VERTEBRATA. 107 



The epithelial roof o the rhomboid fossa is much 

 pleated ; it has been longitudinally bisected and turned 

 to either side. Upon the lower surface of the brain, the 

 great ventral expansion of the hemispheres and their 

 clearly defined median separation can be seen. The 

 hypophysis has been removed and mounted on the left, 

 thus uncovering the large funnel-like infundibulum. 



In this specimen the olfactory organs are also shown. 

 On the left, the floor of the narial chamber has been 

 removed to show the transversely pleated character of the 

 roof. A red rod has been inserted into the anterior and 

 posterior nares on the right. 0. C. 1309 B. 



Saunders, Ann. Mag. Nat. Hist. ser. 6, vol. iii. 1889, 

 p. 157. 



D. 121. The brain of a Mud-fish (Protopterus annectens). It 

 chiefly differs from that of Ceratodus in being shorter and 

 more compact, in the absence of separate olfactory bulbs, 

 and in the feeble development of the cerebellum. In all 

 these features it also more nearly resembles the brain of 

 an Amphibian. 



The cerebral hemispheres are remarkably deep dorso- 

 ventrally, they are united at their posterior end by an 

 anterior commissure situated in the lamina terminalis (this 

 is not shown). 



In front of the ganglia habenulae the epithelial roof of 

 the thalamencephalon is prolonged forwards as a conical 

 paraphysis. The medulla is shorter than in Ceratodus, 

 with the borders of the rhomboid fossa swollen and, half 

 way between the calamus scriptorius and the cerebellum, 

 curved inwards towards the mid-line. There are no de- 

 finite lobi inferiores, but they are possibly represented by 

 the slightly swollen lateral walls of the infundibulum. 

 Burckhardt, Centralnervensystem v. Protopterus, Berlin, 

 1892. 



AMPHIBIA. 

 Osborn, Jour. Morph. vol. ii. 1889, p. 51. 



In the Amphibia, and especially among the Urodeles, the 

 brain is of a remarkably low type and closely resembles that of 

 a Dipnoan. 



