294 THE BIOLOGY OF THE FROG chap. 



growths in the mid-dorsal line, the paraphysis , a vascular 

 outpocketing of the epithelium of the roof, and a short dis- 

 tance behind the latter, the epiphysis, a hollow, thin-walled 

 canal which terminates blindly at its anterior end. A small 

 parietal nerve runs along the dorsal surface of the epiphysis 

 and extends forward over the paraphysis and then passes 

 through the sagittal suture of the skull to end in the brow 

 spot. The epiphysis, which originally was continuous with 

 the brow spot, becomes constricted off from it in early larval 

 life. On the ventral side of the thalamencephalon is the 

 optic chiasma, or crossing of the nerves which go to the 

 eyes. In the frog all of the fibers cross to the opposite 

 side. 



Just behind the optic chiasma is the infundibular lobe, 

 a flattened bilobed structure, emarginate posteriorly and 

 divided by a median longitudinal groove. It is formed of 

 nervous tissue and contains a cavity which is continuous 

 with the third ventricle. 



The hypophysis cerebri lies behind and partly covered by 

 the infundibular lobe. It is composed of an anterior and 

 posterior part; the former is divided into a median, and two 

 lateral portions, the posterior part is flattened and more 

 or less quadrate in outline. Genetically the hypophysis has 

 no connection with the brain, but arises as an outgrowth from 

 the ro'of of the stomodeum. 



The cerebral hemispheres are elongated bodies lying in 

 front of the thalamencephalon ; they taper somewhat ante- 

 riorly and are separated from each other by the sagittal 

 fissure. Their cavities, the lateral ventricles, communicate 

 with the third ventricle by the foramen of Monro ; anteriorly 

 the lateral ventricles extend into the olfactory lobes. 



The olfactory lobes lie just in front of the cerebral hemi- 

 spheres, of which they are but the continuation. They are 



