Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/264

 ANATOMY. Part II. Quadratus Lumeorum five Lumbaris Externus. Uses cf the Mufcles ’which move the Vertebra'. This is a-fmall, oblong, fiat mufcle, irregularly The fealeni, when they adt on each fide at the fame fquare, narrower at its upper than at its lower part, ly- time, may aflift in bringing the neck forward, when we ing along the fides of the vertebrae lumborum, between lean back in any refpedt. When thofe of one fide adl the laft faife rib and the os ilium. by themfelves, a lateral infledHon, either of all It is fixed below to the external labium of almoft all the vertebra oftheythemake neck together, as in bending the the poRerior half of the crifta offis ilium, to the ligamen- middle of the neck ; or. of fome only, as in bending the tum facro-iliacuifi, and a little to the os facrum, by a lower part of the neck alone. fiefhy plane, the fibres whereof run obliquely backward. The longi colli bring the neck forward by the lower From thence it runs up between the facro-lumbaris and of their inferior portions. When one of them adls pfoas, by both which it is partly hid, and is inferted in part or adfs more than the other, this motion is more the extremities of all the tranfverfe apophyfes of the alone, or lefs loins by oblique tendinous digitations. It is likewife fix- By theoblique. upper and gfeateft part of the lowCft portion, ed by a bread infertion in the twelfth rib, on the infide they counterbalance the pofterior mufcles of thefe verteof the ligament that lies between it and the longiflimus bra, and hinder neck from bending backward by the dorfi, by which that rib is connedted to the firft vertebra contradHon of thethefterno-maftoidsi, when, lying on the of the loins. back, we raife the head. The tranfverfalis major, tranfverfalis gracilis, and the little tranfverfales, adting on one fide, can have no other MUSCULI OSSIS COCCYGIS. life but to bend the neck laterally, and to hinder thefe These are fmall, thin, radiated mufcles, lying on inflexions when they adt on both fides. the inner- or concave fide of the os facrum, and neigh- The femi-fpinales of both fides bouring parts of the pelvis. They are four in number, adling together, extendorthetranfverfo-fpinales upon the trunk, to keep two on each fide, whereof one is placed more forward; it from inclining forward in neck Handing or fitting, bend the other more backward; for which reafon the firft backward. The femi-fpinales of one fide adtingandalone, may be termed coccygaus anterior, five ifchio-coccygaut; itproduce the fame motions in an oblique diredtion; and the other coccygaiu pofterior, five facro-coccygaits. that cafe they are aflifted by the inferior or vertebral The coccygceus anterior is fixed by a broad infertion inportion of the neighbouring fplenius, under which they in the anterior portion of the fmall tranfverfe ligament, crofs. at the upper part of the foramen ovale of the os innomifemi-fpinales of both fides may likewife ferVe for natum, which is no more than a particular fold of the theThe of the neck, but then the inferior fplenius of great tranfverfe ligament of the pelvis. From thence it the rotation oppofite fide muft aflift them. runs between this great ligament and the mufculus. obtu- The inter-fpinales are afliftants to the femi-fpinales in rator internus, and, contradiing in breadth, it is inferted their mutual adtion, and may likewife ferve to bring back in the lower part of the os coccygis. neck to its natural fituation, after fmall motions of The coccygaeus pofterior, or facro-coccygseus, is fix- the rotation. ed to the inner or concave edge of the two firlt vertebra The vertebra of the back are moved by being bent of the os facrum, to the inner and lower edge of the li- forward, by being extended or ftraightened, and by being gamentum facro-feiaticum, and to thfe fpine of the os if- infledted diredHy or obliquely toward each fide. The chium. From thence, contradling in breadth, it is in- motion of rotation has no place here, becaufe of the parferted in the infide of the os coccygis above the former ticular ftructure of the joints of thefe vertebra, and their mufcle. connexion with the ribs, which likewife hinder the flexion backward. Flexion and extenfion are the two principal PSOAS PARVUS. motions, and much more apparent than the others. flexion of the back forward is not performed by This is a long flender mufcle, lying upon the pfoas anyTheparticular mufcles, but depends, both in (landing major. and fitting, relaxation of the mufcles that extend It is fixed above by a Ihort tendon, fometimes to the ftraightenonit, the and keep it in that eredt pofture. laft tranfverfe^pophyiis of the back, or higher; fometimes or The two facro-lumbares maintain the back and the to the firft of the loins, and fometimes to both. From regio-lumbaris in their natural when we ftand thence it runs down wholly fiefhy, and more or lefs com- or fit; and by the relaxation offituation fibres more or lefs> plexion the great pfoas, in a diredtion a little oblique. the trunk is proportionably benttheir forward by the weight Having reached the middle of the regio-lumbaris, or bread. They likewife extend the back thereabouts, it forms a flender flat tendon, which gra- ofandtheloinsheadin and all poftures, keep them fteady fixed undually increafing in breadth; like a thin aponeurofis, runs the weight of burdens, and bend the loinsandbackward. over the pfoas major and iliacus internus, at their union, derThe longiflimus dorfi is an afliftant to the facro-lumbaand from thence down to the fymphyfis of the os pubis ris, efpecially to the vertebral portion of that mufcle, and os ilium, and is inferted chiefly in the crifta of the it helps very powerfully, both by the multiplicity os pubis, above the infertion of the pedtineus, fometimes which and infertion of its fibres, in fuftaining the vertebratheof fending an aponeurotic lamina further down.