Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/214

 O M Y. Part I. 174 A N A 1 A little way from this head, we find, on the external conftantly between two bones, they are flatted at both furface, a Imall cavity, where mucilaginous glands are ends, and are thicker, harder, and more liable to offify, lodged; and round the head, the bone appears fpongy, than the other cartilages that are not fubject to fo much where the capfular ligament of the articulation is fixed. preflure. Thefe ribs include the heart and lungs; and Immediately beyond this a flatted tubercle rifes, therefore are the proper or true cuftodes of life. with a fmall cavity at, and roughnefs about its root, for The five inferior ribs of each fide are the falfe or hathe articulation of the rib with the tranfverfe procefs of Jlard, whofe cartilages do not reach to the fternum ; the loweft of the two vertebrae, with the bodies of which and therefore, wanting the refiftance at their fore-part, the head of the rib is joined.—Advancing further on -they are there pointed; and, on this account, having this external furface, we obferve in moll: of the ribs an- lefs preffure, their fubftance is fofter.- The cartilages other fmaller tubercle, into which ligaments which con- of thefe falfe ribs are ftiorter as the ribs defcend. ned the ribs to .each other, and to the tranfverfe procef- To all thefe five ribs the circular edge of the diaphragm fes of the vertebrae, and portions of the longiffimus dorfi, is connected; and its fibres, inftead of being ftretched are inferred. Beyond this the ribs are made flat by immediately tranfverfely, and fo running perpendicular the facro-lumbalis mufcle, which is inferred into the to the ribs, are preffed fo as to be often, efpecially in part of this flat furface farthefi from the fpine, where expiration, parallel to the plane in which the ribs lie. each rib makes a confiderable curve, called by fome its The firft rib of each fide is fo fituated, that the flat angle. Then the rib begins to turn broad, and con- fides are above and below, while one edge is placed intinues fo to its anterior end, which is hollow and fpongy, wards, and the other outwards, or nearly fo; therefor the reception of, and firm coalition with the carti- fore fufficient fpace is left above it for the fubclavian veflage that runs thence to be inferted into the fternum, iels and mufcle; and the broad concave furface is eppofed to the lungs : But then, in confequence of this lituor to be joined with fome other cartilage. To the fore-end of each rib a long broad and ftrong ation, the channel for the intercoftal veftels is not to be cartilage is fixed, and reaches thence to the fternum, or found, and the edges are differently formed from all the is joined to the cartilage of the next rib. This courfe, other, except the fecond •, the lower one being rounded, however, is not in a ftreight line with the rib; for gene- and the other fharp. The head of this rib is not dijally the cartilages make a confiderable curve, the con- vided into two plain furfaces by a middle ridge, becaufe cave part of which is upwards ; therefore, at their infer- it is only articulated wiih the flrft vertebra of the thotion into the flernum, they make an obtufe angle above, rax. Its cartilage is oflified in adults, and is united to and an acute one below.—Thele cartilages, as all others, the fternum at right angles.—Frequently this firft i bhas are firmer and harder internally, than they are on their a ridge riling near the middle of its pofterior edge, where one of the heads of the fealenus mufcle rifes. f arexternal furface. The ribs then are articulated at each end, of which ther forward it is flatted, or fometimes depreffed by the the one behind is doubly joined to thfr vertebra;; for the clavicle. head is received into the cavities of two bodies of the The fifth, fixth, and feventh, or rather the fixth, vertebra, and the larger tubercle is received into the de- feventh, eighth, and fometimes the fifth, fixth, feventb, preffion in the tranfverfe procefs of the lower vertebra. eighth, ninth ribs, have their cartilages at leaft contiguHitherto we have laid down the general flru&ure and ous ; and frequently they are joined to each other by conne&ion of the ribs, and fhall next mark their differ- crofs cartilages; and moft commonly the cartilages of the eighth, ninth, tenth, are connedted. to the former, ences. In viewing the ribs from above downwards, their fi- and to each other, by firm ligaments. gure is ftill ftreighter; the uppermoft being the moft The eleventh, and fometimes the tenth rib, has no tucrooked of any.—Their obliquity, in refpedt of the fpine, bercle for its articulation with the tranfverfe procefs of increafes as they defcend; fo that though their diftan- the vertebra, to which it is only loofely fixed by ligaces from each other is very little different at their back- ments.—The foffa in its lower edge is not fo deep as in part, yet at their fore-ends the diftances between the the upper, ribs, becaufe the veffels run more towards the interftice between the ribs.—Its fore-end is fmaller than lower ones muft increafe. The length of the ribs increafes from the firft and its body, and its Ihort final! cartilage is but loofely connppermoft rib, as far down as the feventh ; and from nected to the cartilage of the rib above. that to the twelfth, as gradually diminifhes. The fu- The twelfth rib is the fhorteft and ftreighteft.—Its perior of the two plain, or rather hollow furfaces, by head is only articulated with the laft vertebra of the which the ribs are articulated to the bodies of the ver- thorax ; therefore is not divided into two furfaces.—tebra, gradually increafies from the firft to the fourth This rib is not joined to the tranfveife procefs of the rib, and is diminilhed after that in each lower rib. - vertebra, and therefore has no tubercle, being often pulThe diftance of their angles from the heads always in- led neceffarily inwards by the diaphragm, which an articreafes as they defcend to the ninth, becaufe of the culation with the tranfverfe procefs would not have allowed.—The foffa is not found at its under edge, be'greater breadth of the facro-lumbalis mufcle. The ribs are commonly divided into true and falfe. caufe the veffeis run below it.—The fore-part of this rib The true coftae are the feven upper ones of each fide, is fmaller than its middle, and has only a very findllwhofe cartilages are all gradually longer as the ribs defcend, pointed cartilage fixed to it.—To its whole internal and are joined to the breaft-hone; fo that being preffed fide the diaphragm is connected. The