VERTEBRATA. 



245 



as many Invertebrates exhibit sensibility and voluntary 

 actions, it follows that analogically the nervous system 

 in them represents both the sym- 

 pathetic and cerebro-spinal systems 

 of Vertebrates. 



The form of the brain differs much 

 among Vertebrates. In some the 

 cerebral hemispheres are small ; in 

 certain Fishes smaller than the optic 

 lobes ; in the higher tribes they near- 

 ly or quite overlap both olfactories 

 and cerebellum. The brain may be 

 smooth, as in most cold-blooded ani- 

 mals, or greatly convoluted, as in 

 Man. 



Vertebrates are subdivided into five 

 classes: Fishes, Amphibians, Reptiles, 

 Birds, and Mammals. The first three 

 are cold-blooded, the other two warm- 

 blooded. Fishes and Amphibians 

 agree in having gills during all or a 

 part of their lives. The rest never 



have gills. FlG> M*- Human Brain 



and Spinal Cord, one fifth 



2. FISHES, (PlSCeS.) These are COn- natural size - Great longi- 

 tudinal fissure, b. Anterior 



sidered the lowest of Vertebrates, yet lobe. c. Middle lobe. d. Me 



,1 dulla oblongata. e. Cerehcl 



they are so numerous as to embrace i ura . /. First spinal =. 

 nearly one half of all Vertebrates, tjgSSZ*^ 



and SO Varied that it is difficult tO salnerves - '.Lumbar nerves 



k. Sacral plexus of nerves for 



frame a definition which shall include the limbs - l - Cauda equina. 



,. The figures indicate the 



all. twelve pairs of cranial nerves, 



FishesHve in the water and breathe 



