THE BRAIN IN SKULLED ANIMALS. 221 



bladder, the twixt-brain (deutopsyche, 0,) proceed primarily 

 the " centres of sight " and the other parts which surround 

 the so-called "third brain -ventricle," also the "funnel" 

 (infundibuluin), the " cone " (conarium), etc. The third 

 bladder, the mid-brain (mesopsyche, m\ furnishes the small 

 group of the " four bulbs," together with the " aqueduct of 

 Sylvius." From the fourth bladder, the hind-brain (meta- 

 psyche, K), the greater part of the so-called " little brain " 

 (cerebellum) develops; the central "worm" (vermis), and 

 the two lateral "small hemispheres." The fifth bladder, 

 finally, the after-brain (epipsyche, n), forms the neck- 

 marrow, or the "elongated marrow" (medulla oblongata), 

 together with the rhomboid groove, the pyramids, olives, etc. 

 The very highest importance must certainly be ascribed 

 to the fact, seen in Comparative Anatomy and Ontogeny, 

 that the brain is originally formed in exactly the same way 

 in the embryos of all Skulled Animals (Craniota), from the 

 lowest Cyclostomi and Fishes, to Apes and Man. In all, 

 the first rudiment of the brain is a simple bladder-like 

 expansion at the anterior extremity of the medullary tube. 

 In all, the five bladders are formed from this simple bladder- 

 like expansion, and in all, these five primitive brain- 

 bladders develop into the permanent brain, with its many 

 complex anatomical arrangements, which afterwards appear 

 in such extremely diverse forms in the various vertebrate 

 classes. On comparing the mature brain of a Fish, an 

 Amphibian, a Reptile, a Bird, and a Mammal, it is hardly 

 conceivable that the several parts of these forms, so ex- 

 tremely different, both internally and externally, may be 

 traced back to one common condition. And yet, all these 

 various brains of Craniota have originated from exactly the 



