Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/338

 Part VI. 2B6 A N A T O M T. name of anus, which has been given to this oeminences which follow each other very regularly, two ridiculous pening, it may be called foramen commune pojierius. large, and two fmall. The firft two great eminences are named corpora Jlriata •, and the fecond, thalami nervo- The gkndula pinealis is a fmall foft greyifh body, aof an ordinary pea, irregularly round, and rum opticorum. The, four fmal! eminences are clofely. bout the frzeof the figure of a pine apple, fituated behind united together; the anterior being called nates, and jiflmetimes thalami nervorum opticorum, above the tubercula the pofterior tejfes. Immediately before thefe tubercles the quadrigemina. It is fixed like a finall button to the lowthere is a lingle eminence, called glandula pincalis. the thalami by two very white medullary pe'Ihe corporaflriata got that name, becaufe in fcraping er part ofwhich at the gland are very near each other, thrm with the knife we meet with a great number of dunculi, almoft tranfverfely toward the thalami. white and afh-coloured lines alternately difpofed, which butItfeparate feems to be moftly of a cortical fobftance, except are only the tranfverfe fe&ion of the medullary and cor- near the where it is Something medullary. tical laminse, mixed together in a vertical pofnion in the Betweenfootftalks, the bafis of the anterior pillar of the fornix, bafis of the cerebrum. and the anterior part of the union of the optic thalami, They lie in the bottom of the fnpenor cavity of the lies cavity or foftiila named infundibulum. It runs lateral ventricles, which they refemble in feme meafure downa towards the bafis of the cerebrum, contra&ing grain fhape, their anterior parts being near the feptum luci- dually, and tenpinates a ftreight courfe, by a fmall dum, from which they feparate gradually as they run membranous, canal, in a infoftifh body fituated in the fella backward, and diminifh in fize. n&mtA glandula pituitaria. The infundibulum The tbalami vsrvorum opiicorum are fo named, be- turcica, above, immediately before the optic thalami, by caufe thefe nerves arife chiefly from them. They are opens two large eminences placed by the fide of each other, an oval hole named foramen commune anterius, and concommunicates with the lateral ventricles. between the pofterior portions or extremities of the fequently At the lower part of the thalami nervorum opticorum, copora ftriata. Their figure is femi-fpheroidal and a dire&ly their union, lies a particular canal, called little oval; and they are of a whitifli colour on the fur- the thirdunder ventricle of the cerebrum. face ; but their inner fuhftance is partly greyilh and part- This canal opens, forward into the infundibulum under ly white. commune anterius, by which it likewife comThefe two eminences are .clofely joined together, and the foramenwith the lateral ventricles. It opens backward at their convex part they are fe far united as really to municates the foramen commune pofterius, between the thabecome one body, the whitifli outer fubftanCe being con- unde? lami and tubercula quadrigemina, oppofite to the final! tinued uniformly over them both. Immediately within this whitiih common fubftance thefe middle canal which goes to the cerebellum. The plexus choroides is a very fine vafcular texture, two eminences are clofely contiguous till about the confifting of a great number of arterial, and venal ramifimiddle of their thicknefs ; and from thence they fepa- cations, partly collefted in two loofe f afciculi, which lie rate infenfibly toward the bottom, where by the fpace one in each lateral and partly expanded over left between them a particular canal is formed, named the neighbouring parts,ventricle, covering in a particular manthe third ventricle, one extremity of which opens for- ner the thalami nervorumandopticorum, glandula pinealis, ward, the other backward. quadrigemina, arid the other adjacent parts At the bottom thefe two eminences are elongated down- tubercula of the cerebrum and cerebellum, to all which it ward toward both fides, into two thick, round, whitifh both cords, which feparate from each other like horns, by a adheres. pituitary gland is a fmall fpongy body lodged in large curvature; and afterwards by a final] curvature theThe between the fphenoidal folds of the dura turned forward in an oppofite direftion to the former, fella turcica It is of a lingular kind of fubftance, which feems and reprefenting the tip of an horn, they approach each mater. neither medullary nor glandular. On the outfide other again. The file of thefe ropes diminiflies gradu- toit isbepartly greyilh and partly reddilh, and white within. ally frora.*their origin to their anterior reunion. The tubercles are four in number, two anterior, and It is tranfverfely oval or oblong, and on the lower part two pofterior; adhering together as if they made but one in feme fubjefts it is divided by a final! notch into two like a kidney-bean. It is covered by the pia body, fituated behind the union of the thalami nervorum lobes, opticorum.. Their forface is v/hite, and their inner fub- mater as by a bag, the opening of which is the extremity of the infundibulum, and it is furrounded by the iiance greyifh,. and are called nates and tejtcs. Diredly under the place where the tubercles of one fmall circular finufes which communicate with the finus Cde are united to thefo of the other fide, lies a finalf mid- cavernofi, dle canal, which communicates by its anterior opening with the third ventricle, under the ihalami nervorum opCEREBELLUM. ticorum, and by its pofterior opening with the fourth The cerebellum is contained under the tranfverfe fepventricle, which belongs to the cerebellum. of the dura mater. It is broader laterally than on Where the convex parts of the two anterior tubercles tum fore or back fides, flatted on the upper fide, and join thefe pofterior convex parts of the thalarai nervorum the inclined both?ways, anfwerable to the feptum, opticorum, an interftice or opening is left between thefe gently which ferves it as a kind of tent or deling. On the four convexities which communicates with the third ven- fewer fide it is rounder; and on the back fide it is divided tricle, and with the fmall middle canal. Inftead of the into-.