382 ELEMENTARY ANATOMY. [LESS. 



The corpora mammillaria may be single, as in the Rabbit, 

 or absent, as in Sauropsida. A pair of inferior prominences 

 may exist below this region of the third ventricle, called lobi 

 infer lores (Fig. 335, 7), which may, but more probably do not, 

 answer to the corpora mammillaria. 



14. The corpora quadrigemina in man are again but feeble 

 rudiments compared with their possible relative development 

 as shown by the brains of other animals. The nates may be 

 smaller than the testes (as in the Hedgehog), or larger (as in 

 the Rabbit). In that this mid-brain region in man bears 

 these four prominences, it agrees with the same part in all 

 Mammals, but among Sauropsidans we find instead, two large 

 rounded hollow spheres (called the optic lobes), placed in 

 Reptiles immediately behind the hemispheres, but in Birds 

 depressed to the side of the brain, below the level of the 

 cerebellum (Fig. 338, 4). 



It is, however, in Fishes that the mid-brain region attains 

 its maximum relative size. This region is considered by 

 most writers to form the optic lobes, but it has been asserted 



FIG. 336. DORSAL ASPECT OF THE BRAIN OF A RAY OR SKATE (Raia latis]. 



i, one of the two olfactory lobes ; 2, the conjoined cerebral hemispheres; 3, the 

 pineal gland : 4, one of the so-called "optic lobes" ; 5, the median structure, 

 commonly called the "cerebellum" ; 6, one of the corpora restiformia. 



to be yet more developed, and to include a part which has 

 generally been regarded (and in all probability rightly so) as 

 representing the cerebellum of higher animals. Thus in the 

 Rays there is a great complex mass folded in numerous 



