THK DKVELOl'MENT OF LEI'IDOSIKKN PARADOXA. 429 



from what is found in Protopteims occurs in the cerebral 

 hemisphere in the much smaller development of the post- 

 olfactory lobe. The " lobus hippocampi " described by 

 . Burckhardt for Protupterus is less distinctly marked off in 

 Lepi do siren, but is still distinctly visible. 



The Development of the Main Topographical 

 Features of the Central Nervous System. 



I now proceed to describe in outline the main features in 

 the brain and spinal cord of Lepi do sir en. The minute 

 structure and details of histogenesis I propose in this general 

 account of the development to leave completely on one 

 side. 



On PI. 27, fig. 10, are given a series of drawings of the 

 brain in side view, and on PI. 26, fig. 8, are given selected 

 stages as seen from the dorsal aspect, and an inspection of 

 these figures will suffice to give a clear idea of the evolution 

 of the external features of the brain without any elaborate 

 verbal description. 



In my description of the early stages in development the 

 brain and spinal cord were left (this Journal, vol. 45, p. 

 23) when they were still in the condition of a partly solid 

 rudiment. From the beginning the anterior or brain region 

 is distinguished by its greater width. 



xVt about Stage 20 or 21 a slight constriction appears 

 marking off the region of the hind brain from the region in 

 front of it. 



At about Stage 25 a transverse wrinkle in the fioor of the 

 brain begins to appear to mark the commencement of cranial 

 flexure. By Stage 26 (fig. 10 a) this has become well marked. 

 A slight bulging on each side of the thalamencephalon at this 

 stage marks the rudiment of the cerebral hemisphere. 



By Stage 29 (cf. fig. 10 b) the cranial flexure has become 

 more pronounced, and a depression of the brain-roof has 

 begun to show itself in the region of the anterior limit of the 

 hind l)raiii. The anterior corner (if the liiiid bniiii has o-imiwh 



