| XXX | (173) | XXX |
173 Part I. A N A T O M Y. that adheres very firmly to its circumference. From Each os innominatum affords a focket (the acetabuthis membrane chiefly the two obturator mufcles, exter- lum) for the thigh-bones to move in, and the trunk of nal and internal, take their rife. The great defign of the body rolls here fo much on the heads of the thighthis hole, befides rendering the bone lighter, is to allow bones, as to allow the moft confpicuous motions of the a ftrong enough origin to the obturator mufcles, and trunk, which are commonly thought to be performed by fufficient fpace for lodging their bellies, that there may the bones of the fpine. be no danger of difturbing the fun&ions of the contained The pelvis then has a large opep above where it is vifcera of the pelvis by the adKons of the internal, nor continued with the abdomea, is ftrongly fenced by bones of the external being bruifed by the thigh-bone, efpecial- on the fides, back, and fore-part, and appears with a ly by its lefler trochanter, in the motions of the thigh wide opening below, in the Ikeleton; but, in the recent inwards.' -The bowels fometimes- make their way fubjedi, a confiderable part of the opening is filled by through the nitch for the veffels, at the upper, part of the facrofciatic ligaments, pyriform, internal obturator, this thyroid hole, which caufes a hernia in this place. levatores ani, gemini, and coccyg.xi mufcles, which fupIn the external furface of the ofl’a innominata, near port and protedf the contained parts better than bones the outfide of the great hole, a large deep cavity is form- could have done; fo that fpace is only left at the loweft ed by all the three bones conjunftly: For the os pubis part of it, for thd large excretories, the vefica urinaria, conllitutes about one fifth ; the os ilium makes fomething inteftinum redtum, and in females, the uterus, to diflefs than two fifths, and the os ifchium*as much more charge themfelves. than two fifths. The brims of this cavity are very high, The T,hor ax, or chejl, reaches from below the neck and are (till much more enlarged by the ligamentous car- to the belly; and, by means of<the bones that guard it, tilage, with which t^iey are tipped in a recent fubjedt. is formed into a large cavity : The figure of which is From this form of the cavity it has been called acetabu- fomewhat conoidal. lum ; and, for a diftinguilhing charadter, the name of the The bones which form the thorax are the twelve dorbone that conflitutes the largeft fhare of it is added; fal vertebra; behind, the rihs on the fides, and the Jlertherefore acetabulum oflis ifchii is the name this cavity num before. commonly bears.——Round the bafe of the fupercilia The vertebra have already been deferibed as part of the bone is rough and unequal, where the capfular liga- the fpine. ment of the articulation is fixed. The brims at the The- Ribs, or cofia, (as if they were cujlodei, or upper and back-part of the acetabulum are much larger guards, to thofe principal organs of the animal machine, and higher than any where elfe ; which is very necefl’ary the heart and lungs), are the long crooked bones placed to prevent the head of the femur froth flipping out of its at the fide of the cheft, *in an oblique diredfion downcavity at this place, where the whole weight of the bo- wards in refpedt of the back-bone. Their number is dy bears upon it, add confequently would otherwife be generally twelve on each fide; though frequently eleven conftantly in danger of thrufting it out. As thefe or thirteen have been found. brims are extended downwards and forwards,, they be- The ribs are all concave internally ; where they come lefs; and at their internal lower part a breach is are alfo made fmooth by the adtion of the containmade in them; from the one fide of which to the other, ed parts, which, on this account, are in no dangef of a ligament is placed in the recent fubjedt; under which a being hurt by them; and they are convex externally, large hole is left, which contains a fatty cellular fubftance that they might refift that part of the preflure of the atand vefidls. Befides this difference in the height of mofphere, which- is not balanced by the air within the •the brims, the acetabulum i§ otherwife unequal: For lungs, during infpiration. The ends of the ribs next the lower internal part of it is deprefled below the carti- the vertebrae are rounder than they are after thefe bones laginous furface of the upper-part, and is not covered have advanced forwards, when they become flatter and with cartilage; into the upper-part of this particular de- broader, and have an upper and lower edge, each of preflion, where it is deepelt and of a femilunar form, the which is made rough by the addon of the intercoftal mufligament of the thigh-bone, commonly called the round cles, inferted into them.—The upper edge of the ribs is one, is inferted; while in its more fuperficial lower part morei obtufe and rounder than the lower, which is deprefthe large mucilaginous gland of this-joint is lodged. The fed on its internal fide by a long fofla, for lodging the largeft: fhare of this feparate depreflion is formed in the intercoftal veflels and nerves; on each fide of which os ifehium. to which the intercoftal mufcles are
- The ofla innominata are joined at their back-part to there isThea ridge,
fofla is not obfervahle however at either end each fide of the os facrum by a fort of future, with a Very fixed. of the ribs: for, at pofterior or root, the veflels have thin intervening cartilage, which ferves as fo much glue not yet reached the the ribs ; and, at the fore-end, they are to cement thefe bones together ; and ftrong ligaments go fplit away into branches, to ferve the parts between the from the circumference of this unequal furface to connedt them more firmly. The offa innominata are con- ribs.At the pofterior end of each rib, a little head is nedted together at their fore-part by the ligamentous car- formed, which is divided by a middle ridge into two tilage^interpofed between the two ofla pubis.—Thefe bones plain or hollow furfaces ; the loweft of which is the can therefore have no, motion in a natural ftate, except broadeft and deepeft in moft of them. The two plains what is common to the trunk of the body, or to the os are joined to the bodies of two different vertebra, and facrum. the ridge foroes itfelf into the intervening cartilage.— • Voi.. I. No. 8. 3
