78 PHYSIOLOGICAL SERIES. 



the rest; it is the representative of the single furrow in such 

 torn; >nt /tias. The medulla is a good example of 



the elongated open type ; in it, the several prominences 

 are very clear, more particularly the arrangement of the 

 convoluted auricles and the lobus linoae lateralis. 



0. C. 1311 A. Presented ly Sir E. Home, Bart. 



D. 76. The brain of a Porbeagle (Lamna cornuUcd) divided in 

 the median sagittal plane, and with the halves so mounted 

 as to show the lateral and median surfaces. 



This brain (fig. 21) reaches a comparatively high state of 

 development ; it is distinguished by its antero-posterior con- 

 cent rat ion, the large size of the fore-brain and optic lobes, 

 and the excessive development and structural complication of 

 the cerebellum. The fore-brain is globular and, owing to the 



Brain of Lamna rormtbica, in sagittal section. 



immense thickening of the lamina terminalis, almost solid, 

 it-* ventricle (best seen at the back of the left-hand specimen) 

 _ all hut obliterated. The olfactory peduncle- are narrow 

 at their origin from the antero-lateral parts of tin- cerebrum 

 and gradually become inflated as they approach the small 

 olfactory bulbs. In this part their walN are extremely thin 

 (see the cut edges of a -.|iiare window in the figure). It 

 seems likely that the small size of the olfactory bulbs is 



ipensated by the ^reat development of the cerebrum. 

 The thalamencephalon is very short compressed between 

 the cerebrum and the large optic lobes. The latter are com- 

 pletely covered dorsally by the cerebellum. The structure 

 of the cerebellum is well shown in the right-hand specimen : 



