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 Part I!. A N A T O M Y. 2 14' The fibres that come from the left ala, crofs over The fcalenus fecundus is fixed a little more backward thofe from the right ala, and this again fends a fmali in the external labium of the upper edge of the lecond fafciculu^ of fibres over thofe of the left ala ; afterwards rib, fometimes by two feparate portions, and fometimes without any divifion. The anterior portion is fixed imthe two crura part from each other. The right crus is larger and longer than the left, and mediately under the pofterior portion of the firft fcaleis always inferted in the four upper vertebrae of the loins, nus, by a fhort flat tendon, united a little with the firft and often in the fifth likewife, by the fame number of intercoftal mufcle. From thence it runs up over the podigitations, which become more and more tendinous as fterior portion of the firft fcalenus, communicating likethey defcend, and at length are expanded in form of an; wife with that mufcle, and is fixed by infertions, partly aponeurofis. This crus lies more on the middle of the tendinous and partly flefliy, in the tranfverfe apophyfes of the four firft vertebne of the neck. bodies of the vertebras than on the right fide. The left crus is fmaller and Ihorter, and lies more on The pofterior portion is fixed in the fecond rib, more the fides of the vertebras. It is fixed by digitations to backward than the other. From thence it runs up, bethe three upper vertebra of the loins, feldom reaching ing divided into two portions, whereof one is inferted in lower. The lower part of it is expanded in the fame the tranfverfe apophyfes of the three firft vertebrae of the manner as the other ; and the two expanfions fometimes neck, behind the fcalenus primus. The other portion runs up behind the former, and is inferted in the tranfmeet together. The oval opening of this inferior mufcle of the dia- verfe apophyfes of the two firft vertebrae. phragm, gives paflage to the extremity of the osfophagus, and the aorta lies in the interftice between* the two SERRATUS POSTICUS SUPERIOR. crura. Immediately above the opening or hole, a thin fafciculus of fibres is fent off to the ftomach. This is a flat thin mufcle, fituated on the upper part In the middle aponeurofis of the gieat mufcles, a little of the back. It is fixed on one fide, by a broad ato the right of the anterior part of the Hope, near the poneurofis, to the lower part of the pofterior cervical •fmall mufcle, is a round opening, which tranfmits the ligament, and to the fpinal apophyfes of the two laft trunk of the lower vena cava. The border or circum- vertebrae of tfie neck, and two firft of the back. ference of this opening is very artfully formed by an ob- From thence it runs down a little obliquely forward, lique and fucceffive intertexture of tendinous fibres, al- and is inferted, by broad flelhy digitations, in tlje poftemolt like the edge of a wicker balket; and is, confequent- rior part of the fecond, third, fourth, and fometimes of ly, incapable either of dilatation or contradtion, by the the fifth true ribs, neai their angles; but fometimes it adtion of the diaphragm. has no infertion in the fecond rib. We find therefore three confiderable openings in the diaphragm; one round and tendinous, for the paffage of SERRATUS POSTICUS INFERIOR. the vena cava; one oval and flelhy, for the extremity of the cefophagus ; and one forked, partly flefhy, and part- This is a flat thin mufcle, lying on the lower part of ly tendinous, for the aorta. The round opening is to the back. It is fixed in the laft fpinal apophyfis of the the right-hand, clofe to the upper part of the right ala back, and in the three firft of the loins, by a broad apoof the fmall mufcle ; the oval opening is a little to the neurofis. From thence it runs up a little obliquely, and left; fo that the right ala, which is between thefe two is fixed, by flefhy broad digitations', in the laft fourfalfe holes, lies almoft diredly over againlt the middle of the ribs. Its infertions, in the loweft rib, is near the cartibody of the eleventh vertebra of the back; the tendi- lage, and, in the other three, near their angles. nous fr*k is under the oval opening, but a little more toward the middle. INTERCOSTALES. The intercoftal mufcles are thin, flelhy planes, lying S C A L E N I. in the interftices between the ribs, their fibres running These are compound mufcles, irregularly triangular. obliquely from one rib to another. In each interftice lie The fcalenus primus is fixed to the upper part of the two planes, an external and an internal, clofdy joined tooutfide of the firft rib, by two dillindl portions, called gether, nothing but a thin, fine, cellular, membranous coming between them. commonly branches; one anterior, the other pofterior. webAccording to this natural divifion, there muft be forThe anterior branch is fixed to the middle portion of the rib, about an inch from the cartilage. From thence ty-four intercoftal mufcles in the twenty-two interftices it runs obliquely upward, and is inferted in the tranf- left between the twenty-four ribs ; and of thefe there verfe apophyfis of the fixth, fifth, and fometimes of the are eleven external, and eleven internal, on each fide. The fibres of the external intercoftals run down from third vertebra of the neck. • The pofterior branch is fixed more backward in the behind forward, and, thofe of the internal intercoftals firft rib, an interllice of about an inch Feing left be- from before backward; fo that the fibres of thefe two tween it and the other branch, through which the axil- feries of mufcles crofs each other. lary artery •and brachial nerves are tranfmitted. From The external intercoftals extend commonly from the thence it runs up obliquely behind the former, and is in- vertebrae to the extremity of the upper labium of the bony portion of each rib, and go no further. Theternal inferted in all the tranfverfe apophyfes of the neck.