Functions of the Cerebrum. 639 



between the nerve and the lens in front. l This sort of an eye is thus 

 shown to have been the property of the earliest vertebrates, and it was 

 single and median. It existed in the earlier reptiles, such as the ich- 

 thyosaurus and plesiosaurus, along with the bilateral eyes, and in the 

 course of ages it has become superseded by them. This third eye was 

 no doubt functional in the case of the labyrinthodont, a fossil amphi- 

 bian, since there is a large orifice in its skull for the passage of the 

 nerve from the pineal gland to the eye. More or less trace of the 

 pineal eye is discovered in various reptiles, as iguanas, chameleons, fly- 

 ing lizzards, geckos, &c. Even in birds there is a rudiment of it, and 

 a trace is to be found even in mammals. The pineal gland, which was 

 originally the sensory ganglion of the median or pineal eye, persists 

 very remarkably in all vertebrates except the very lowest. The pineal 

 gland is therefore most certainly the remnant of a sense apparatus which 

 formerly included an eye and a connecting nerve. The question arises, 

 why, since the eye and the nerve disappeared so long ago, the correspond- 

 ing piece of brain has not disappeared too. To my mind there is only 

 one solution, and that is, that this piece of brain has remained func- 

 tional. Its original office was to receive the sight impressions from the 

 pineal eye, and in former times it must have constituted a relatively 

 larger part of the brain than now. But this ganglion is connected with 

 the rest of the brain, and no doubt undergoes waste and repair the same 

 as the rest. In short, its function, although changed in detail, must 

 still, to some extent, subserve a purpose similar to its original one. As 

 the hand has been gradually modified from a fin by new habit and use, 

 so I take it a new use has been gradually put upon the pineal gland. 

 Its position and connections, as well as its pedigree, would indicate that 

 its functions are sensory. It is single and median, which indicates that 

 its functions are related to both sides alike. In all probability it is 

 commissural between the two sides of the sensory tract of the crura 

 cerebri, and helps to establish sensory equilibrium between the comple- 

 mentary halves of the corpora quadrigemina and of the optic thalami. 



CHAPTER LXIII. 



FUNCTIONS OF THE CEREBRUM. 



The establishment of the true theory of the functions of the cerebrum 

 of course necessarily overthrows any false theories which may have been 

 entertained. Phrenology is one of these theories, and as it has gained 

 wide acceptance, it may be well enough to point out the error of theory 

 on which it is based. 



The theory of the Phrenologists is, that the brain is the organ of the 

 1 See fijf. isi. 



