THE BRAIN AND ITS MENINGES. 153 



These are the main particulars of the interior of the brain ; 

 the anatomy of which consists only of a quantity of hard 

 words, to which it is hoped future investigations may attach 

 a meaning and a use. 



Turn up the brain now to its base. The soft masses ex- 

 tending anteriorly and looking like a prolongation of each 

 hemisphere, are the first pair of nerves or olfactories {Plate 

 V, Fig 1.1) going to the nose, and conferring the sense 

 of smell. They are peculiar for having sinuses within them 

 {Plate V. Fig 1 . a), and also for not taking on the cha- 

 racter of nerves till they reach the sieve-like plate of the 

 ethnoid bones ; when they divide into a vast number of 

 very fine nerves. The next pair are the optic, and go to 

 the eye for sight {Plate V. Fig 1.2). They are behind 

 the olfactory, and come from each hemisphere to meet in 

 the middle, and there unite {Plate V. Fig 1 . &). They 

 are peculiar for taking out of the cranium a layer of dura 

 mater, also for having an artery within their centres — the 

 ophthalmic {Plate V. Fig 2 . 9) ; as well as for their decus- 

 sation ; for if the right eye goes blind the optic nerve 

 withers, and in that state can be distinctly traced to the 

 left hemisphere. 



The cerebellum, or little hrain, rests upon the tentorium 

 or bony process given off towards the interior of the cra- 

 nium by the os triquatrum. The tentorium, however, is only 

 partly formed of bone ; and partly of reflections of the dura 

 mater. It is placed immediately behind the cerebrum, which 

 it divides from the cerebellum. It is supposed to be of use 

 to prevent the brain being shaken in animals that leap much. 

 The cerebellum when divided displays the white matter ar- 

 ranged in an arborescent manner ; which is called the arbor 

 vitce. The dura mater, beside forming processes, also enters 

 into the composition of sinuses. The sinuses at the top 

 and back of the brain are first one above, and another at the 

 bottom of the falx, called the superior and inferior longitu- 

 dinal sinuses. These two are connected at the bottom by 

 the straight sinuses ; into which the veins from the interior 

 of the brain empty themselves. These sinuses discharge 

 their contents into the two lateral sinuses, which empty 

 themselves into the jugular veins. 



The ophthalmic veins empty themselves into the ophthal- 



