36 PROF. T.J. PARKER ON CARCHARODON RONDELETII. [Jail. 18, 



The urinary bladder (specimen C) is small and opens into the in- 

 fernal compartment of the cloaca by a small papilla (fig. 17, ur.ap.). 



7. The Brain. 



The brain could only be examined in specimen C, in whicli, as 

 already mentioned, decomposition was far advanced before the fish 

 came into my possession. As soon as the cranium could be removed, 

 a saturated solution of corrosive sublimate was poured into the brain- 

 cavity through the foramen magnum, so as to harden the brain in 

 situ. Next day the roof of the cranium was sawn off, and the brain 

 sketched from above (Plate VII. fig. 20) ; a plate of mica was then 

 inserted beneath it, the nerves cut, and the organ transferred to 

 strong alcohol with comparatively little shaking. By using these 

 precautions, and thanks in great measure to the thickness of the pia 

 mater, I was able to make a tolerably accurate examination of tiie 

 brain, although all the softer abdominal viscera were hopelessly 

 decomposed some days before the brain could be got at. The ence- 

 phalon of the foetal specimen E was also examined (Plate VIII. 

 fig. 29). 



The adult brain is about 13 cm. long from the anterior boundary of 

 the prosencephalon (Plate VII. figs. 20-22, prosen.) to the posterior 

 end of the metencephalon ' or medulla oblongata {meten.) ; to this 

 must be added about 1 2 cm., the length of the olfactory lobes (rkinen.), 

 giving a total length of 25 cm. The greatest width, across the 

 cerebrum, is about 3'5 cm. In the foetus (fig. 29) the brain is 

 nearly 5 cm. long by 2 cm. wide. 



The main difference between the foetal and the adult brain depends 

 upon the elongation, in the latter, of the medulla oblongata and of 

 the olfactory lobes. As will be seen by comparison of figs. 20 and 

 29, fully one half of the medio-dorsal region of the metencephalon 

 is covered by the cerebellum in the foetus, hardly more than one 

 sixth of it in the adult. Again, in the foetus, the olfactory bulbs 

 are almost sessile upon the prosencephala, their crura being very 

 short; in the adult, on the other hand, the rbinencephalic crura 

 are of great length. 



In a female specimen of Lamna cornuhica, 135 cm. {4\ ft.) long, 

 I find that the brain resembles that of the fcetal rather than that of the 

 adult Carcharodon ; the olfactory crura are comparatively short, not 

 longer than the prosencephala, and fully one half of the metence- 

 plialon is covered by the cerebellum. In the fresh brain the optic 

 lobes were so completely covered by the cerebellum as not to be 

 visible in a view from above, but after hardening in corrosive sublimate 

 the epencephalon had undergone a slight shrinking, allowing the 

 lateral regions of the lobes to be seen. The vertical height of the 

 entire brain is great in proportion to its width; probably in the 

 adult Carcharodon the decomposed brain had spread out a good deal 

 under the action of gravity. 



In the metencephalon of Carcharodon the restiform bodies (fig. 20, 



^ Vide T. J. Parker, " On the Nomenclature of the Brain and its Cavities." 

 ' Nature,' vol. xxxv. 1886, p. 208. 



