36 DISSECTION OF THE FACE. 



Action. The fibres enlarge the nasal opening by raising and everting 

 the outer edge. 



The DEPRESSOR AL^E NASi (fig. 5, 6 ) will be seen if the upper lip is 

 everted, and the mucous membrane is removed from the side of the fraenum 

 of the lip. It arises below the nose from a depression of the upper jaw- 

 bone above the roots of the second incisor and canine teeth ; and ascends to 

 be inserted into the septum nasi and the posterior part of the ala of the nose. 



Action. By drawing down and turning in the edge of the dilated nostril, 

 it restores the aperture to its usual size. 



MUSCLES OF THE EYELIDS. The muscles of the eyelids and eyebrow 

 are four in number, viz., orbicularis palpebrarum, corrugator supercilii, 

 levator palpebrse superioris, and tensor tarsi :* the two latter are dissected 

 in the orbit, and will be described with it. 



The ORBICULARIS PALPEBRARUM (fig. 6, 2 ) is the sphincter muscle 

 closing the opening between the eyelids. It is a flat and thin layer, 

 which extends from the margin of the lids beyond the circumference of 

 the orbit. From a difference in the characters of the fibres, a division 

 has been made of them into two parts outer and inner. 



The external fibres (orbital part), the best marked, are fixed only at 

 one point, viz., the inner angle of the orbit. This attachment (origin) is 

 connected with the surface and borders of the small tendo palpebrarum ; 

 above that tendon with the nasal process of the upper maxillary, and the 

 internal angular process of the frontal bone ; and below the tendon with 

 the superior maxillary bone, and the margin of the orbit. From this 

 origin the fibres are directed outwards, giving rise to ovals, which lie side 

 by side, and increase in size towards the outer edge of the muscle where 

 they project beyond the margin of the orbit. 



The internal fibres (palpebral part), paler and finer than the outer, 

 occupy the eyelids, and are fixed at both the outer and inner angles of 

 the orbit. Internally (origin) they are united with the tendo palpebrarum, 

 and externally (insertion) with the external tarsal ligament and the malar 

 bone, and some few may blend with the orbital part. Close to the cilia 

 or eyelashes the fibres form a small pale bundle, which is sometimes called 

 ciliary. 



The muscle is subcutaneous ; and its circumference is blended above 

 with the occipito-frontalis. Beneath the upper half of the orbicularis, as 

 it lies on the margin of the orbit, is the corrugator supercilii muscle with 

 the supra-orbital vessels and nerve ; and beneath the lower half is part of 

 the elevator of the upper lip. The outer fibres are joined occasionally by 

 slips to other contiguous muscles below the orbit. 



Action. The inner fibres cause the lids to approach each other, shut- 

 ting the eye ; and in forced contraction the outer commissure is drawn 

 inwards. In closure of the eye the lids move unequally the upper being 

 much depressed, and the lower slightly elevated and moved horizontally 

 inwards. 



When the outer fibres contract, the eyebrow is depressed, and the skin 

 over the edge of the orbit is raised around the eye, so as to protect the 

 ball. Elevation of the upper lip follows contraction of the outer part of 

 the orbicularis, in consequence of fibres being prolonged to the levator 

 labii superioris. 



1 The tensor tarsi muscle (p. 59) is sometimes described as a part of the orbicu- 

 laris. 



