106 PHYSIOLOGICAL SERIES. 



resembles that of a Urodele Amphibian. It is, tor instance, 

 MTV long and narrow, with spacious ventricles enclosed 

 by thin or, in parts, epithelial walls. 



The medulla is very like that of a low Shark long, and 

 MTV broad ill front with a widely open rhomboid fossa and 

 well marked medullary auricles. It gradually merges into 

 the cord behind. The highest development is shown by 

 the cerebral hemispheres, which are large, like those of 

 Amphibia, and greatly expanded in their ventral parts. 

 They are separated from one another in the mid-line as far 

 back as the anterior commissure. Their walls are thin and 

 even purely epithelial in their dorso-median parts, where 

 they are closely attached to a large glandular paraphysi- 

 that projects from the roof of the thalamencephalon wedge- 

 like between them. In front, the lateral ventricles are 

 continued by a narrow passage into the cavities of a pair 

 of strong olfactory bulbs. In the possession of definite 

 olfactory bulbs Ceratodus differs markedly from Protopterus 

 Of the Amphibia, and shows more resemblance to Ela-mo- 

 brauchs. A window has been cut in the left hemisphere 

 and olfactory bulb to show the continuity of their cavities 

 and the relation of the glandular paraphysis to the me>ial 

 wall of the hemisphere. 



The tlialaniencephalon ai:d mesencephalon, as. in Urodeles, 

 are very long and narrow. The former shows a pair 

 of strongly marked ganglia habenuhe. The epiphysis, 

 which is not shown in the specimen, is .small. The optic 

 - form a single prominence of small size between the 

 thalumencephalon and the cerebellum. It is narrower in 

 front than behind, and is divided mesially by a conspicuous 

 but narrow <l.-irk band due to a local thinning of the roof. 

 Tlie cerebellum is slightly damaged ; it is more strongly 

 loped than in Amphibia, though less so than in Fi>he>. 

 and forms a broad transverse band behind the optic lobes, 

 continuous laterally with the medullary auricles. 



In the floor of the fourth ventricle lie a pair of small 

 fasciculi bogitadinalei po-leriores. and ill the lateral walls, 

 rather far back, a pair of longitudinal ridges the va^al 

 lob<>, which in position resemble those of Sharks but are 

 without fcheir characteristic nodulation. 



