86 PHYSIOLOGICAL SERIES. 



From the above it will be seen that the hinder part of 



the lirain i- clo-dy -imilar to that of an Elasmobranch, parti- 

 cularly in the conformation of the cerebellum and medulla. 

 The optic lobe- -how a .-light .tendency towards the Teleostean 

 type in having an enlargement on their lateral walls 

 Ulggestive d' th-- torus -cmidivulari-. but the hypothalamus 



to essentially thai of an Kla-mohrandi. The cerebrum in 

 it- relation to the olfactory bulbs, in the considerable separa- 

 tion of the hemispheres and the relative thickness of their 

 dor-al and ventro-lateral walls, is closely similar to that of 

 a Dipnoan or low Amphibian. 



Wilder, Proc. Ac. Sci. Philad. 1877, p. 219. 



OANOIDEI. 



D. 86. Part of the skull of a Sturgeon (Adpenser sturio) with 

 the brain exposed from the dorsal and ventral aspects. In 

 comparison with the size of the fish (this individual weighed 

 154 Ibs., and measured 6 ft. 4 in.) the central nervous 



system i- peculiarly -mall. The brain occupies only a part 

 of the spacious cranial cavity, and in its superficial features 

 combines characters found in Elasmobranchs, Amphibia, 

 and Teleostea: for example, the medulla resembles that 

 of a low Shark or Amphibian, whereas the cerebellum is 

 very similar to that of Ceratodus but is provided with a 

 valvula as in Teleosts. Or, again, the mid-brain and 

 thalamencephalon have a strong superficial likeness to 

 those, .of Ceratodus, whereas the cerebrum resembles that 

 of a Teleostea n in having an epithelial pallium. 



The medulla broaden- gradually from the cord towards 



tin- cerebellum, and has a very widely-open rhomboid fo--a 



covered by a -trough pleated vascular roof (removed and 



mounted on the left in the -pecimen). In its floor are a 



pair of well-marked fa-ciculi longitudinales, each of which 



ll a -truug offshoot to the motor root of VII. In the 



hinder part of the rhomboid fossa on either side lie the 



nodulated a> in Sharks. To the side 



and in front d' tin- \a-al lubes, the margin of the rhomboid 



i .-\\dl- tu form a conspicuous lobe on either side ( lohus 



line.-e lateral)-) that _ Main iicrxe- of the 



