BRA 



to the coipora qiindii^cmina. It opens above into tlielliiid 

 vcntncle, by intans of tlie canalis mcJiiis ; its tcnninatioii 

 would open bilow towards the back of the medulla fpiiialis, 

 were it not clofed by pia mntcr. The brain may now he 

 tumtd over tX) expofe the balls. The lower and anterior 

 part of the third ventricle is clofed by a cineritious fubllance 

 of a conical form, which extends from the anterior conimif- 

 furc and crura cerebri to the jiindion of the optic nerves, 

 where its apex is continued, under the name of infiindibuliim, 

 to the pituitary gland. This body is lodged in the fella 

 tiircica, the upper aperture of which is aintraftcd by a fi)ld 

 of the dui-a mater. Its fuperior furface is plane ; its inferior 

 convex. Its fubllance is harder tlian that of the brain. 

 Immediately behind the infundibnlum arc fccn two fmall 

 convex medullary eniinencts, named the corpora fubrotuuda, 

 candieantia, or mamiliaria, from uhieh tlie anterior crura 

 fornicis and the pedunculi of tlie pineal gland commence. 

 The crura cerebri (proccfl'us mcdullie cerebri of Soemmer- 

 ring) are two large medullary proctdes, having a fibrous ap- 

 pear..nce externally, wliich come from the middle and con- 

 vex part of the hemifplieres. They are feparated above 

 and in front, approach below and behind, and meet toge- 

 ther juft before they terminate in tlie medulla oblong.ita. 

 There is feen therefore a depreflion, or hollow, between 

 thefe crura in front, from which the third pair of nerves 

 arifes, and which is called by Vicq d'Azyr la fofle des nerfs 

 oculo-mufculaires. 



The cerebellum is lodged in the pofterior and inferior 

 foffa of the bafis cranii ; it is fituated therefore under the 

 cerebrum, in a peculiar cavity, formed chiefly by the occi- 

 pital bone, the poilerior furface of the petrous part of the 

 temporal bone, and the tentorium. Its upper furface is 

 nearly flat ; the under and pollerior are convex. It forms 

 in front fome prominences named appendices vermiformes. 

 It is divided into a right and left lobe, by a hflure which 

 does not extend very deeply, and which lodges the falx 

 cerebclli. The cerebellum confifts, like the cerebrum, of 

 an intermixture of cortical and medullary matter; but 

 they have m.t the fame relative arrangement as ifi the 

 cerebrum. The furface of the cerebellum is marked by 

 ieveral horizontal lines, not difpofed concentrically, into 

 which the pia mater dtfcends to a confiderable depth, 

 and from which other divifions containing alfo proceffes 

 ot pia mater commence. The cerebellum has, therefore, 

 a much more extenfive furface than an equal bulk of cere- 

 brum ; and the cortical matter is more abundant than the 

 medu ary. On a vertical feaion we fee a thick cord of 

 meduUar)- matter fending off proccffes, from which other 

 branches proceed, and all of which are furrounded by 

 cortex ; this is the arbor vitae. An horizontal feclion dif- 

 covers feveral parallel curved portions of cortex and medulla 

 fucceedmg each other alternately. The trunk of the arbor 

 v'tK conltitutes the crus cerebelli on each iide, which joins 

 the medulla oblongata. 



_ The medulla oblongata is a large protuberance occupy- 

 ing the lower and middle part of the cranium, and rell- 

 •ng on the baf.lar proccfs of the occiput. It is formed 

 the crura cerebclli and cerebri, which have been al- 

 ■ defcribed. Its furface has an irregular and fibrous 

 1>> _ ice. It is divided into a right and left portion by a 



Hich contains the bafilar artery. This body is 

 -ons Varolii, tuberculum annulare, or nodus 

 '^■' A the V '""^''^ "'"'^ P^*^" ^'■°'" '^^ pofterior part to 



"'^ W\ A rot. """""^ "lagiui^i occipitale, and enter the 



"' th mieU the Xv ' "=""<= "^ medulla fpinalis. It is fepa- 

 ^'^„.\ canal under th. '■o'" by a circular contraftion. The 

 t d from the pone Vi- 'lary cord forms a bulb or dilated 

 "pper part of this rufdv 



appeata^ 

 cr.oove, '.'■• 



BRA 



part, which is divided into four convexities, of which tli* 

 two fuperior are named corpora olivaria, the two inferior 

 corpora pyramidalia. For the moll ample and fatisfaftory 

 information on the anatomy of the brain, we refer the reader 

 to the Encefalotomia Nuova univerl'ale di Vincenzo Mala 

 carne, Torino, 17H0; the Traite d'Anatomie of Sabatier, 

 vol. ii. ; the fourth volume of Soemmerring's work " De cor- 

 poris humani fabrica ;" and his dilTertation " Ucbcr das or- 

 gan dcr Seele." Above all, however, the ■' Traite d'ana- 

 tomie, et de phyfiologie, avcc des planches colories," Pari<:, 

 17S6, folio, of Vicq d'Azyr, requires the greateft com' 

 mendation. In this fuperb work all the parts of the brain 

 are reprefented of their natural colour, with fuch fidelity and 

 beauty as render it, beyond difpute, the grandeil book, 

 which has ever been publillitd in liluftration of the human 

 frame. 



We (hall fubjoin to this defcription of the brain, a brief 

 account of the anatomy of the medulla fpinalis, and nerves. 

 Thus, we dial! include in one article, the ilruaure of the 

 fcnforium, of the organs which tranfmit imprcffions to it, 

 and convey the determinations of the will from it ; which 

 are only to be confidered as parts of one circle of actions. 

 ^ Sfnicliire of the Medulla Sptnahs. 

 This part is a continuation, as we have already mentioned 

 from the medulla oblongata, which is formed by the iinioa' 

 of the medullary appendices of the cerebrum, and cerebellum'. 

 The bulbous portion, which we have before defcribed as 

 forming the corpora pyramidalia and olivaria, is the com- 

 mencement of the medulla fpinalis ; although, as it is con- 

 tained 111 the cranium, the term of fpinai marrow cannot, 

 with Unci propriety, be applied to it. 



The medulla fpinalis confilb externally of medullary mat- 

 ter ; on making a tianfverfe fediou, we find a portion of 

 cmentious fubllance in the centre, confifting of two ftripes 

 which crofs each other, thus X. When covered by its 

 membranes, it is of a firmer confiftence than the brain; but 

 It fpeedily difTolves when laid bare. Its form is nearly cy- 

 hndncal, but it is comprefl'ed before and behind. A groove 

 extends along its anterior and pofterior flat furface, and 

 thefe imprefiions feem to divide it into two cords. It is 

 larger in the bottom of the neck, and towards the lower 

 part of the back, thaain the intermediate fpaces. It con- 

 traftsm the lumbar region into a conical form, and ttrmi- 

 nates by a fmall filament, which is fixed to the bottom of the 

 mealh of dura mater. 



It fends off a pair of nerves at each interval between the 

 vertebr.1;, which are named cervical, dorfal, lumbar, or fa- 

 cral, according to the region in which they arife. Thefe 

 nerves are produced by two fafciculi of fibres, one of which 

 comes from the front, the other from the back of the cord 

 1 hele are feparated by a membrane, which xvill be prefently 

 mentioned, and penetrate the dura mater by two diftinft 

 holes, after which they unite to form a ganglion. The ar- 

 tenes of the dura mater are derived from many fources ; the 

 vertebrals furnifli an anterior and pofterior one. The others 

 are derived from the cervical, intercollal, lumbar and facral 

 arteries, which enter at the openings, through which the 

 nerves go out, and communicate with the fpinai branches 

 of the vertebrals, fo as to keep up their fize to the end of 

 the medulla fpmahs. The vems, which are alfo numerous, 

 pour^their blood into two longitudinal finufes, formed in 

 the Qura mater which lines the vertebral canal, and ex- 

 tending the whole length of that canal. Thefe communi- 

 cate together by tranfverfe portions at the intervals of the 

 vertebra;, i hey communicate in the neck with the verte- 

 bral veins ; in the back, with the intercoftals ; and below, 

 with the lumbar and facral veins 



S The 



