78 COMPARATIVE ANATOMY. 



from one another by a cavity traversed by a single commis- 

 sural band. Immediately in advance, the olfactory lobes 

 arise; they are particularly large in Selachia. Pituitary 

 body well developed; infundibulum generally long, as in 

 Gadus (haddock). Pineal body a small globe of gray matter 

 situated between optic lobes, very distinct in Anguilla (eel); 

 less apparent in other species. In Salmo (salmon) it consti- 

 tutes a plexus of slender vessels, anastomosing to form a 

 club-shaped mass. In Squalus (shark) it is particularly dis- 

 tinct, being larger than in any other fish (Wyman). The 

 brain, as a whole, is small, and forms but about j^ part of 

 the axis. It does not fill the brain case, a quantity of loose 

 adipose tissue being placed around it. 



Batrachia. Spinal cord extends the length of the verte- 

 brae excepting in some tailless forms, as Rana (frog). Brain 

 resembles in general features that of Pisces. The region of 

 cerebellum less developed ; the cerebellum is a small flat- 

 tened transverse band continuous on either side with medulla 

 oblongata, which is without lateral lobes. Optic lobes large, 

 conspicuous. Cerebrum larger than in Pisces, and extends 

 with but slight or no constriction into large olfactory lobes. 

 Optic thalami and corpora striata present. Each portion of 

 the brain hollow, and lined with ciliated epithelium, except- 

 ing optic thalami and cerebellum, which are solid. 



Reptilia. Spinal cord contains a canal which in Sauria 

 and Ophidia extends as far as the first coccygeal vertebrae. 

 In Chelonia it is shorter. Brain. The cerebellum consists 

 of a median portion only. The fourth ventricle is open from 

 above, but is closed in Chelonia. Optic lobes of a rounded 

 form, and contain a ventricle which communicates with the 

 third ventricle. 



The posterior portion of each lobe is constricted trans- 

 versely in Python. Cerebral hemispheres more developed 

 than in fishes, larger than optic lobes, smooth, hollow, and 

 imperfectly subdivided into lobes. Each hemisphere enfolds 

 a portion of pia mater and contains upon the base of its 

 ventricle representatives of the corpora striata and optic 

 thalami. The third ventricle is traversed by the anterior 



