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 22 1 O M Y. fes, and is inferred by its other extremity in the middle of the infide of the ramus of the lower jaw, near the infertion of the external portion with which it mixes. The third portion, which is leaft and mod internal, is fixed by one extremity to the inner labium of the low'er edge, and alfo to the infide of ahnoft all the zygomatic arch; and by the other, to the root or bafis of the coronoid apophyfis, where it mixes wholly flefliy with the infertion of the middle portion. TEMPORALIS. This is a broad flat mufcle, refembling the quadrant of a circle in figure. It occupies all the femi-circular or femi-oval plane of the lateral region of the cranium, the temporal fofla, and part of the zygomatic foffa. From this fituation it has its name. To conceive,- juftly the infertions of this mufcle, it muft be obferved, that the pericranium is divided into, two laminae. The internal lamina, fometimes taken for a particular periofteum, covers immediately all the bony parts of this region. The external lamina fe.parated from the other, is fpread out like an aponeurotic or ligamentary tent, by means of its adhefions to the external angular apophyfis of the os frontis, to the pofterior edge of the fuperior apophyfis of the os malse, and to the upper edge of all the zygomatic arch, all the way to the root of the maftoid apophyfis. This mufcle is compofed of two planes of flefliy fibres, fixed to the two fides of a tendinous plane nearly of the fame breadth with them, like a concealed middle tendon ; as may be plainly feen by dividing the mufcle all the way to the bone, according to the direftion of its fibres. The body of the mufcle thus formed is inclofed between the two aponeurotic or ligamentary laminse in the follow'ing manner. The internal fleftiy plane is fixed, by a broad radiated infertion, to all the femi-circular plane of the cranium, by the intervention of the internal lamina of the Sect. XVI. .The Muscles which move the periofteum. Thus it is fixed to the lateraF external part of the os Lower Jaw. frontis, and to its external ahgular apophyfis, to the lower part of the os parietale, to the fquamous portion of the os temporis, to the great ala or temporal apophyfis MASSETER. of the fphenoidal bone, by which the temporal fofla is This is a very thick flelhy mufcle, fituated at the formed; and a little to the backfide of the internal orbiback part of the cheek. It feems to be made up of three tary apophyfia portions, like a triceps, viz. one large and external por- zygomatic fdfla.of the os malae, which forms part of the tion, one middle, and one fmall and internal. The external portion is fixed by one tendinous extremity to all the inferior edge of the os malae, and a little •PTERYGOIDj£US MAJOR five INTERNES. to the neighbouring parts of the os maxillare and apo- This mufcle lies on the infide of the lower jaw, alphylis zygomatica of the os temporum. From thence it in the fame manner as the mafleter does on the outruns down obliquely backward, being wholly flelhy, and moft being of the fame figure with that mufcle, only is inferred by the other extremity in the rough impreflion fide, fmaller and narrower. on the outfide of the angle of the lower jaw. The middle portion is fixed by one end to the lower It is fixed above in the pterygoid cavity, chiefly to edge of the whole apophyfis zygomatica of the os tem- the infide of the external ala of the apophyfis pteryporum, and a very little to that of the os malae. From goides. thence it runs down a little obliquely forward in an op- It runs down obliquely toward the angle of the lower pofite diredlion to the firft portion, under which it crof- jaw, and is infsrted a little tendinous in the inequaliVot. 1. No. 10. 3 3K ties

Part II. A N A T the back and loins while extended, whether in fitting or Handing, and' in preventing their linking under the weight of the bod3', or of any additional burdenr It aifilts in performing and in counterbalancing all the motions and inflexions of which thefe vertebrae, efpecially thofe of the loins, are capable in all pollutes of the body. All the fpinales and tranfverfales of the back and loins belonging to the clafs of the vertebrales red!, the fpinales to the middle mufcles, and the tranfverfales to the lateral, their chief ufes mull be to allift, moderate, and maintain the motions of extenfion and lateral inflexion, whether fimple and dired, or oblique and compound. The femi-fpinales, or ..tranfverfo-fpinales, being oblique, converging, vertebral mufcles, are allillants to the facro-lumbaris and longiflimus dorfi, which they crofs on each fide. The quadratus lumborum and pfoas parvus are of the fame ufe to the vertebras of the loins, as the fcaleni to thofe of the neck. When both quadrati ad, they keep the lumbar pillar llraight, that is, fo as not to incline to either fide, and then they may allift the redi of the abdomen in the inflexions forward, and the fuperior portions of the obliqui in lateral inflexions. They may likewife ferve to fupport the haunches alternately in walking; and, in Handing on one foot, the quadratus of the oppofite fide may fupport the haunch of that fide. The pfoas parvus, ferves to fuftain.the pelvis much in the fame manner with the mufculi redi of the abdomen, in climbing, &c. The coccygaeus anterior may fuftaip the coccyx in aequilibrio, and hinder it from being bent backward, ami from being luxated in great drains, as in the excretion of hardened faeces, &c. The coccygasus polterior can only ferve to replace the os coccygis when it has been forced backward, and to hinder it from being luxated backward.