428 .r. (IHAHAM KKKR. 



Eventually the hypophysis becomes hei'e as elsewhere 

 closely united with the infundibuluni, its dorsal portion 

 becoming partly penetrated by tubular outgrowths of the 

 latter (saccus vasculosus, cf. p. 432, Text-fig. 2, H). 



Central Nervous System. 



As the brain of the adult Lepidosiren • has never before 

 been investigated in the fresh condition, I give on Plates 

 26 and 27 figures illustrating its conformation, and showing 

 the roots of the cranial nerves, including those of the fourth 

 and sixth, whose existence in Lepidosiren has hitherto been 

 doubted. By a comparison Avith Burckhardt^s figures of 

 Protopterus it will be seen that the two brains are very 

 similar. In dorsal view the only difference is in the relative 

 size of the different parts. In Lepidosiren the mid-brain 

 region is relatively longer, the thalamencephalon relatively 

 shorter than in Protopterus. Li my figure I have not 

 shown the extensive system of outgrowths from the saccus 

 endolymphaticus which here, as in Protopterus, overlies and 

 to a great extent hides the region of the hind brain. 



In the ventral view of the brain the cerebral hemispheres 

 are not sharply marked off from the thalamencephalon. The 

 swelling at the base of the olfactory nerves is much more 

 conspicuous, owing to the smaller size of the post-olfactory 

 lobe which underlies them. ^Fhe lobi inferiores are much 

 more strongly developed, the hypophysis is more rounded in 

 form, and the hind brain is like the cerebral region less broad 

 from side to side as conijiared with the thalamencephalon. 



In the side view of the brain the most striking difference 



' In dissectJiiL,' the brain ol' Lepidosiren one is struck by the extra- 

 ordinary development of richly ramifying blood-vessels within the cranial 

 cavity, forminj^ a packing all round the brain. This may possibly be an 

 adaptaliou tu the times al. which it. is iinpo5sil)le to make the blood rich in 

 oxygen, during the final stages in drying up of the bwami)s, or during casual 

 rainfalls in the dry season. 



