Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/340

 ANATOMY. Part VI.
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cords, which go obliquely from the fubftance of one late- the bony canal, fo that it is larger in the vertebrae of the neck than thofe of the back. ral portion into the fubftance of the other. The corpora olivaria and pyramidalia are whitifh emi- It fends off from both the fore and back fides, at difnences fituated longitudinally near each other on the ferent diftances, flat fafciculi of nervous filaments. The lower fide of the extremity or cauda, immediately be- anterior and pofterior fafciculi having got a little'beyond hind the tranfverfe or annular protuberances. The Cor- the edge of the medulla, unite in pairs, and form on pora olivaria are in the middle, fo that the interftice be- each fide a kind of knots, ceWthganglions by anatomifts, tween them, which is a kind of fuperficial groove, an- each of which produces a nervous trunk. Thefe gangli1'wcrs to the inferior groove of the following portion. -bns are made up of a mixture of cortical and medullary The corpora pyramidalia are two lateral eminences fubftance, accompanied by a great number of fmall blooddepending on the olivaria. Thefe four eminences are fi- veffels. The dura mater, which invefts the medulla, fends out tuated on the lower half of the medulla. The tubercula mammillaria, or papillae medullares, on each fide the fame number of vaginae as there are which are fituated very near the produdion of the infun- ganglions and nervous trunks. Thel’e vaginae are produftions of the external lamina; the internal lamina, which dibulum, have been taken for glands. Thefe tubercles feem to have fome immediate relation is very fmooth and polifhed on the infide, being perforated by two fmall holes very near each other, where to the roots or bales of the anterior pillar of the fornix. each vagina goes off, through which holes the extremiThe beak or tube of the infundibulum is a very thin production from the fides of that cavity; and it is ftrength- ties of each anterior and pofterior fafciculus are tranfmitted ; and immediately after their paffage through the cned by a particular coat given to it by the pia mater. internal lamina, they unite. It is bent a little from behind forward, toward the glandula pinealis, and afterwards expands again round this gland. Uses of the Brain and its Appendages in general. The membrana arachnoides, or external lamina of the was the firft who difeovered the brain to pia mater, appears to be very diftindly feparated from be Malphighi or an organ fitted to feparate fome particular the internal lamina, in the interftices between all thefe fluida gland, the mafs of blood. eminences on the lower fide of the medulla oblongata, Thefrominfinite number of fmall fecretory clufters ftrain without any vifible cellular fubftance between them. the mafs of blood carried to them by the nuFrom this medulla oblongata, arife almoft all the or filterramifications, and feparate from it an excelfivenerves which go out of the cranium through the diffe- merous fluid ; the remaining blood being conveyed back, rent bafis is perforated. like- lyby fine the fame number of venal extremities, into the finufes wife foramina produces bythewhich medullaits fpinalis, which is noIt more mater, and from thence into the jugular and than a common elongation of the cerebrum and cerebel- of the duraveins. lum, and of their different fubftances ; and therefore the vertebral This fubtile fluid, commonly called animalfpirit, medulla oblongata may juftly be faid to be the firft ori- nervous juice, or liquor of the nerves, is continually gin or primitive fource of all the nerves of the human Forced into the medullary fibres of the white portion of body. the cerebrum, cerebellum, medulla oblongata, and medulla fpinalis ; and by the intervention of thefe fibres MEDULLA SPINALIS. fupplies arid fills the nerves, which are a continuation of The medulla fpinalis is only an elongation of the ex- them. tremity of the medulla oblongata; and it has its name from PERICRANIUM. itsfequently being contained in the orbonycommon canal ofappendix the fpinaofdorfi cona continuation the ; cerethe external integuments of the head, the brum or cerebellum, as well becaufe of the two fubftances Ikin,Besides hair, and cellular fubftance, there is an aponeuroof which it is compofed, as becaufe of the membranes by tic expanfion which covers the head like a cap, and is which it is invefted. round the neck and on the {boulders like a ridingThe dura mater, after it has lined the whole internal fpread hood. , furface of the cranium, goes out by the great occipital This aponeiirofis Is very' ftrong on the head, and it foramen, and forms a kind of funnel, in its progrefs appears to be made'up at leaft of two ftrata of fibres crofdownward through the bony Canal of the vertebrae. As it is fptead on the neck it becomes The fpinal marrow is made up of a cortical and me- fing each other. thinner, and ends mfeijfibly, on the davicles. dullary fubftance, as the cerebrum and cerebellum ; but gradually It fends out a production on each fide, from above downwith this difference, that the alh-coloured fubftance lies ward, and from without inward, which having paffed o-within the other; and in a tranfverfe fetftion of this me- ver the fuperior extremity of the mufculus fterno-maftoidulla, the inner fubftance appears to be of the figure of daeus, runs behind that mufcle toward the tranfverfe apoan horfe-lhoe. , of the vertebra; of the neck, where it communiThe bodv of the medulla fpinalis runs down all the phyfes cates with the ligamenta inter-tranfverfalia. way to the firft vertebra of the loins, where it terminates The external furface of all the bones of the head, as in a point. The fize of it is proportionable to that of well