!; PHYSIOLOGICAL SERIES. 



remarkable size, pressing in front against the corpora 

 ttriata and overhung posteriorly by the cerebellum ; they 

 ore globular in shape, separated in the mid-dorsal line by 

 a shallow groove. Upon the antero-lateral surface of each 

 i- an indentation from which emerges the main part of 

 the optic tract. The lobule that lies postero-ventral to the 

 indentation is due to an overlapping of the tectum opticum. 

 The right optic nerve crosses below the left ; both are of 

 great size, although the eyes in this fish are comparatively 

 -mall. The cerebellum is of moderate size ; it is egg- 

 >hap'd, with its narrow end projecting forwards over the 

 hinder half of the optic lobes. The crura cerebelli are 

 strongly pronounced. The medulla is much shortened 

 antero-posteriorly. 0. C. 1380 A 18. 



D. 99. The cranium of a Mackerel (Scomber scombrus) with the 

 brain exposed from above. The roof of the optic lobes and 

 the anterior free end of the cerebellum have been removed 

 to show the valvula cerebelli. This organ occupies the 



Fig. 27. 



Valvula cerebelli of Scomber scombrus. 



major part of the cavity of the optic lobes and is to a great 

 nt responsible for their size. It consists of a mitral 



lobe directly continuous with the cerebellum, and of two 



literal lobes or wings formed by the reduplication of the 



anterior ends of the central lobe. 



This relation of the lobes to each other is shown in the 



diagram I fiL f . '21). 



D. 100. The skull of a Fishing-Frog (Lophius piscatorius) with 

 the brain exposed from the dorsal and ventral aspects, and 

 with the origins, and in some cases the peripheral parts, of 

 the cranial nerves shown. 



