Edinger, Comparative Psychology. 439 



is developed. From these parts of the brain fibers extend back- 

 ward through a long stalk, and in this stalk probably lie also tracts 

 which lead into theforebrain from the peripheral region supplied by 

 the trigeminal nerve. Then ventrally there is a much folded sac, 

 the hypothalamus, upon which lies the hypophysis, while dorsally 

 there is a hollow sphere, the roof of the mid-brain, wherein termi- 

 nate the optic nerves which maybe seenemerging from the chiasma 

 just in front of the hypothalamus. The cerebellum rises in 

 prominent folds over the roof of the mid-brain and behind it one 

 sees a large lobe situated laterally on the oblongata. Here ter- 

 minate the nerves for the sense of hearing and for the lateral line 

 sense. Below is seen the oblongata which is very well developed, 

 because even in Chimaera the cranial nerves which emerge from 

 it are extraordinarily large. 



This apparatus is thoroughly suited by its inner connections, 

 which are now well known, for the reception of sense impressions 

 from the outside world and for conveying them to various places 

 whence groups of motor ganglion cells send out their nerves to 

 the muscles. It also includes a number of special regulatory 

 mechanisms, amongst which the cerebellum is most important. 

 The motor mechanisms are everywhere united into motor-com- 

 plexes in such a way that a sensory impulse brings about the move- 

 ment, not of a single muscle, but always of a group of muscles 

 adapted for some special action. 



Even isolated parts of the palaeencephalon are capable of simple 

 reactions. For example, a ring cut from the neck region of a 

 male frog embraces the female, if the skin of the breast comes in 

 contact with the skin of the female, exactly as the whole animal 

 does (GoLTz). In fact, the embracing reflex may be induced even 

 if one rubs the skin of the male with the juice of eggs. I need not 

 in this place point out that all the mechanisms for movement — 

 swimming, flying, and the like — are so lodged in the palaeencephalon 

 that the animals are able to execute these movements for some 

 time after the removal of the neencephalon. This was demon- 

 strated two thousand years ago by the ostriches which ran about 

 Rome's arena with their heads pierced by arrows. 



No part of the palaeencephalon can be absent without a corre- 

 sponding function becoming lost, and all parts develop in size 

 according to the demands which the activities of the animal make 

 upon them. A knowledge of the degree of development is of the 



