Comparative Anatomy of the Bruin. 577 



ami exterior wall of the optic lobes, and into tin- walls of the third ven- 

 tricle. A small part only, in osseous fishes. are continued past the 

 third ventricle into the cerebrum. This shows, as will be seen, that a 

 comparatively small portion of the activities of the fish are governed by 

 reflection and memory. 



The next division of the brain is represented in the embryo by what 

 Carpenter calls the vesicle of the third ventricle. Huxley denominates 

 it the Thalamencephalon. Owen includes it with the optic lobes in the 

 Mesencephalon. The constant parts of this division are the pineal 

 gland, or conarium, above the third ventricle, and the pituitary gland, 

 or hypophysis, below it. These glands are to be found in all osseous 

 fishes, as well as in birds, reptiles and mammals, including man. The 



Olj 



FIG. 288 Brain of Cod. Top 



0//.^Olfactory Lobes. 



P. Cerebrum. 



G Cerebellum. 



Op Optic Lobes. Top of the 

 left one removed, showing 



V. The ventricle and 



e. Two of the four interior op- 

 tic tubercles. 



FIG. 289. Brain of Cod. Un- 

 derside. 

 P. Cerebrum. 

 Py Pituitary Gland. 

 O. Optic Lobes. 

 n. Hypoarin. 

 h. Haematosac lying between 



the hypoaria. 

 2. Optic Nerves. 

 3, 6, 6, 7, 8. Cranial nerves of 



corresponding numbers. 



( Owen.) 



FIG. 289. 



optic thalamus itself is either not developed at all 

 or is extremely elementary in the fishes. The pineal 

 FIG 288 gland is usually a pyramidal sac joined at its base 



to the walls of the third ventricle between the optic and the cerebral 

 lobes. The apex is attached to the roof of the cranium. It is com- 

 monly composed of a membranous substance well supplied with blood 

 vessels. It has this character in the sturgeon, lepidosiren and shark. 

 In the carp and herring tribes there is medullary matter incorporated in 

 the membrane, and in some fishes there is gray matter. 



The pituitary gland is likewise a very vascular body, at the apex of 

 un inverted conical, membranous sac, the infundibulum. It is attached, 

 base upward, to the underside of the crura cerebri, its cavity opening 

 into the third ventricle. 



The fibres of nerve matter from the spinal cord, after forming the 

 crura cerebri, are continued forward to the bodies called the cerebral 

 hemispheres, in fishes ; bodies which, in the higher vertebrates, appear 

 to constitute only the corpora striata This division of the brain is 



