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The under surface of the brain exhibits beneath the cerebellum the continuation 

 forwards of the medulla oblongata which forms as it were the stalk supporting the 

 dorsal lobes. Beneath the front part of the optic lobes, however, an inferior outgrowth 

 is seen ; this consists of a pair of lobes called the lobi inferiores between which is a 

 vascular organ called the pituitary body, or hypophysis cerebri, supported on a hollow 

 conical outgrowth called the infundibulum. 



The brain contains a central cavity which is the continuation of the central canal of 

 the spinal cord. This cavity terminates in the middle line between the cerebral 

 hemispheres, but laterally it sends off two diverging prolongations into the interior of 

 these hemispheres. The medulla oblongata and its continuation, the crura cerebri, are 

 situated below the central cavity, while the cerebellum, the optic lobes, and the upper 

 part of the cerebral lobes are enlargements of the roof of the cavity. The infundibulum 

 and pituitary body form a downward diverticulum of the cavity beneath the point 

 where it bifurcates into the cavities of the cerebral lobes ; and a corresponding diver- 

 ticulum towards the dorsal side exists between the anterior part of the optic lobes, and 

 is called the pineal gland. The pineal gland, like the pituitary body, is a vascular 

 structure in fishes. In some reptiles it has been found to have a structure resembling 

 that of the vertebrate eye. 



The olfactory lobes are continuous with the inferior portion of the cerebral hemi- 

 spheres. In the sole the left olfactory lobe is somewhat larger than the right, a difference 

 which is related to the great development of the left olfactory capsule. But there is no 

 inequality in the size of the optic lobes or optic nerves, such as that which according 

 to Owen occurs in the halibut and some other Pleuronectidce. In Owen's figure of 

 the halibut the right optic lobe and left optic nerve are the larger ; the eyes of this 

 species, as of the sole, are on the right side, so that the larger structures are those 

 belonging to the eye which has migrated. 



It would naturally be inferred that the left eye was larger than the right in the 

 halibut, but I have not been able to find any allusion to an inequality in the size of the 

 eyes themselves. 



As in all bony fishes the brain of the sole is much smaller than the cavity in which 

 it lies. The widest part of the cavity within the skull is the posterior part : here the 

 brain passes forwards from the foramen magnum as an axis in the centre of the cavity, 

 the surrounding space being occupied by the auditory organs. The sacculi meeting 

 in the middle line below, occupy the space below the brain, while the semicircular 

 canals intervene between the latter and the skull-walls dorsally and laterally. A 

 transverse ridge on the inner surface of the skull-wall, forming part of the sphenotic 

 and prootic bones, limits anteriorly the cavity occupied by the sacculi. In front of 

 this ridge is another ventral depression occupied by the optic thalami and pituitary 

 body, while above the optic lobes and cerebral hemispheres there is a considerable 

 space occupied only by spongy connective tissue containing fluid the arachnoid 

 membrane. The internal hollow of the parasphenoid bone in front of the pituitary 



K 2 



