358 



PHYSIOLOGICAL SERIES. 



of the branches of the " fissure," which do notissume the 

 peculiar radiating grouping found in the Porpi o's brain. 



The chief sulci form a series of concentric res around 

 the " Sylvian fissure," the lowermost of whic are much 

 more acutely flexed than is the case in th Porpoise. 

 There is little exact information to guide us in ctermining 

 the exact homologies of these five great arc, but it is 

 customary to call them from below upwards : () the ecto- 

 sylvian, (ii.) the suprasylvian, (iii.) the ectolateil, (iv.) the 

 lateral, and (v.) the entolateral sulci, respective! (figs. 203 

 and 204). In the depths of the " Sylvan fissur" there is 

 a very large submerged area, which is usually jrnied tho 

 "insula," although it cannot be regarded as the strict 

 homologue of the human " island of Reil." 



On the mesial surface the most peculiar feairo is tho 

 enormous rostrum of the corpus callosum (fig. 25). 



Fig. 205. (x*.) 



SULC INTERCAL. 5PLE;N 



SULC. GEN:"' 



GENU. 



' OPT. THAL. 



POST. CORP. CALL. 



There is a very deep cingular arc formed by le united 

 calcarine, intercalary, and what we may call tho ptagenual 

 sulci (fig. 205). 



Beyond this arc the irregular tangle of sulci Iocs not 

 permit any satisfactory analysis. 



Guldberg, Forhand. Vidensk. Selsk. Christiam, 1885, 

 p. ID. 



D. 525. A cast of tho cnmi;il cavity of a young Ilorqu; (Balw- 

 noptera musculus). 





