208 PISCES. 



face of the medulla oblongata probably replace, as in other higher 

 Vertebrata, the pons Yarolii, that occurs only in the Mammalia. 

 The cerebellum is a large spherical ganglion, for the most part 

 slightly lobular in form, and curved upon itself posteriorly ; it is des- 

 titute of transverse grooves, but frequently furnished with obtuse 

 lateral projections. The fourth ventricle extends far into it. In 

 front of the cerebellum are situated two large obovate hemispheres 

 or ganglia, which in size, form, and situation, are similar to the 

 hemispheres of the higher animals, and, from their forming the most 

 considerable portion of the brain of the Osseous Fishes, have been 

 regarded as such by some anatomists ; others term them optic 

 lobes, and they obviously correspond to the mesocerebrum, the cor- 

 pora quadrigernina and optic thalami of the human subject taken 

 conjointly ; they may be called median lobes. Upon making a super- 

 ficial section of one of them, we find beneath a thin roof of medul- 

 lary matter, a large cavity extending through the whole ganglion. 

 Upon the floor of this cavity or ventricle, in the posterior direction, 

 are usually situated four small round ganglia (e. g., in Perca, Esox, 

 some Salmonidae, Clupea, Trigla, Gadus Lota), more rarely two (as 

 in Gadus, Lophius, Blennius, Muraena, Cyclopterus, some species 

 of Pleuronectes), or six (e. g., Scomber thynnus, Salmo trutta) ; 

 these ganglia certainly appear to resemble the corpora quadrigernina 

 of Man, and are even united with the cerebellum by some fasciculi 

 of fibres, the crura cerebelli ad corpora quadrigernina. Further out- 

 wardly lies a larger ganglion, similar to the optic thalamus or corpus 

 strtiatum, and on its external side we perceive a radiated expan- 

 sion of fibres, called the staff-wreath, or corona radiata. Several 

 transverse fibres or commissures are found, which partly correspond 

 to the corpus callosum, partly to the commissura mollis ; a rudiment 

 also of the fornix probably exists. The hollow space included be- 

 tween the above-named ganglia is prolonged deeply into the infun- 

 dibulum, and thence backward into the fourth ventricle, and cor- 

 responds itself to the third. Inferiority and posteriorly, at the base 

 of the brain, and behind the chiasma or decussation of the optic 

 nerves, are situated a pair of mostly large ganglia, which agree 

 in their position with the eminentiae candicantes of the human sub- 

 ject, but can not certainly be compared with them. They are usually 

 styled the lobi inferiores, are oval in form, and rest for the most 

 part upon the pituitary body. In front of the pair of mesocerebral 

 masses (lobi optici) are situated another pair of smaller yet tolerably 

 distinct ganglia, which are united also posteriorly by a narrow me- 



