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 Part II. A N A T O M Y. 215 ternal begia forward near the itemum, and end back- fixed, by their upper extremities, fo near the articulation of the ribs with the vertebras, that they cannot deprefs ward at the angle of each rib. that rib in which they are fo inferted ; whereas the infertions of their lower extremities in the following SUPR A-COSTALES. rib being at a greater diftance from the articulation, These mufcles are irregularly triangular, and fituated they may move that rib upward. And from thence it on the back-part of the ribs, near the vertebras. follows, that all the remaining part of each external inEach of thefe mufcles is fixed, by one tendinous ex- tercoftal which terminates at the bony extremity of each tremity, in the tta.nfverfe apophyfis, which lies above the rib, can only ferve to raife the Wer rib toward the articulation of each rib, and to the neighbouring liga- upper. inefit; the firft being inferted in the tranfverfe apophyfis The anterior fibres of the internal intercoftals are fa of the lafl: vertebra of the neck ; and the lad, in that of near the articulation of the ribs with the fternum, that the eleventh vertebra of the back. they cannot deprefs drat cartilage in which each of them From thence the flefiiy fibres run down obliquely, in- is inferted ; whereas the inferior infertions,of thefe fibres, creafing in breadth as they defeend, and are inferted in being at a greater diftance from the articulation, they are the back part of the outfideof the following rib. in a condition to raife the cartilages in which they are fo inferted. From whence it fellows, that all the internal intercoftal mufcles have the fame ufe with the external, S U B-C O S TALE S. and that they can have no other. These are fleihy planes, of different breadths, and The fupra-coftales are powerful afliftants to the intervery thin, fituated more or lefs obliquely on the infides coftals in their common adtion, and are therefore very of the ribs, near the bony angles, and running in the juftly termed levatores coflarum. fame direflion with the external intercoftals. The fterno-coftales deprefs the cartilaginous portions, They are fixed by both extremities in the ribs; the and anterior extitmities die ribs, efpecially the fupeinferior extremity being always at a greater diftance from rior ribs, except the firft;of and the fame time draw the vqrtebrae than the fuperior, and feveral ribs lying be- the cartilages of the inferior ribsat near the fternum, by tween the two infertions. reafon of the curvature. They may therefore very well be called depreffores cojlarum, as the fupra-coftales are StE RNO-Co ST ALE S VlllgO TRIANGULARIS StERNI. named levatores. fub-coftales having the fuperior extremities of These are five pairs of flefliy planes, difpofed more theirThefibres much more diftant from the vertebral articuor lefs obliquely on each fide the fternum, and on the in- lation of ribs than the lower extremities, it follows, fide of the cartilages of the fecond, third, fourth; fifth, that they the' can more eafily move the upper than the Jower andfixth true ribs. ribs, and confequently that they are afiiftants to the They are inferted, by one extremity, in the edges of fterno-coftales. the infide of all the lower half of the fternum. From The diaphragm, together with the intercoftal mufcles, thence the firft miifcle on each fide runs up obliquely, and the ribs, fternum, and vertebras of the back, forms the is fixed in the cartilage of the fecond rib. The fecond cavity of the thorax, and it divides this cavity from that runs Jefs obliquely to its infer tion in the cartilage of the abdomen. third rib. The refi are inferted, in tire fame manner, in of Itstheparticular ufe is to be the principal organ of refpithe cartilages of the following ribs. ration, is, of the alternate expanfioh and contradion This laft mufcle is fixed, by one extremity, in the of the that thorax. The other mufcles already mentioned cartilage of the fixth true rib, near the bone, and feems are to be confidered only as afliftants and direftors, in to pafs the appendix enfiformis, immediately above the order to facilitate thefe motions, which, in infertion of the diaphragm in that appendix, and to join the ordinary ftate, andare regulate perpetual, but which may, by the the mufcle on the other fide. adlion.of thefe other mufcles, be accekrated, retarded,' or even befufpended for fome fpace of time. Uses of the Mnfcles employed in Refpiration. The diaphragm may move when the ribs are at reft,, and confequently without the afliftance of the mufcles The fealeni are fometimes ranked among thefe which which the ribs ; and this motion may be fufficient ferve for refpiration; but they ought rather to be rank- to keepmove ed among the mufcles which move the vertebras of the thorax. up the alternate dilatation and contraction of the neck; becaufe the articulation of the firft rib on both fides, with the firft vertebra of the back, feems to ferve only for the motion of that vertebra on the rib, and not Sect. XIV. The Muscles which move the. of the rib on the vertebra. Head <tn the Trunk. The ferrates pofticus fiiperior is difpofed to move upwards the three or four upper ribs next the firft. The ferratus pofticus inferior is. ftili better difpofed for Sterno-Mastoidasus five M-astoid-zeus Anterior, deprefiing and keeping down the laft three or four falfe This is a long, narrow, pretty thick, and rncftly. ribs. The pofterior fibres of the external intercoftals are fleihy mufcle, fituated obliquely between the back part