ORBITAL REGION. 243 



the lachrymal sac, and the origin of the Levator labii superioris, and the Levator 

 labii superioris alaeque nasi muscles. Internally, it is occasionally blended with 

 the Pyramidalis nasi. Externally, it lies on the temporal fascia. On the eyelids, 

 it is separated from the conjunctiva by a fibrous membrane and the tarsal car- 

 tilages. 



The Corrugator Supercilii is a small, narrow, pyramidal muscle, placed at the 

 inner extremity of the eyebrow beneath the Occipito-frontalis and Orbicularis 

 palpebrarum muscles. It arises from the inner extremity of the superciliary ridge ; 

 its fibres pass upwards and outwards, to be inserted into the under surface of the 

 orbicularis, opposite the middle of the orbital arch. 



Relations. By its anterior surface, with the Occipito-frontalis and Orbicularis 

 palpebrarum muscles. By its posterior surface, with the frontal bone and supra- 

 trochlear nerve. 



The Levator Palpebrse will be described with the muscles of the orbital 

 region. 



The Tensor Tarsi is a small thin muscle, about three lines in breadth and six in 

 length, situated at the inner side of the orbit, behind the tendo oculi. It arises 

 from the crest and adjacent part of the orbital surface of the lachrymal bone, and, 

 passing across the lachrymal sac, divides into two slips, which cover the lachrymal 

 canals, and are inserted into the tarsal cartilages near the puncta lacrymalia. 

 Its fibres appear to be continuous with those of the palpebral portion of the Orbi- 

 cularis; it is occasionally very indistinct. 



Nerves. The Orbicularis palpebrarum and Corrugator supercilii are supplied by 

 the facial and supra-orbital nerves ; the Tensor tarsi by the facial. 



Actions. The Orbicularis palpebrarum is the sphincter muscle of the eyelids. 

 The palpebral portion acts involuntarily in closing the lids, and independently of 

 the orbicular portion, which is subject to the will. When the entire muscle is 

 brought into action, the integument of the forehead, temple, and cheek is drawn 

 inwards towards the inner angle of the eye, and the eyelids are firmly closed. 

 The Levator palpebras is the direct antagonist of this muscle ; it raises the upper 

 eyelid, and exposes the globe. The Corrugator supercilii draws the eyebrow 

 downwards and inwards, producing the vertical wrinkles of the forehead. This 

 muscle may be regarded as the principal agent in the expression of grief. The 

 Tensor tarsi draws the eyelids and the extremities of the Tachrymal canal inwards, 

 and compresses them against the surface of the globe of the eye ; thus placing 

 them in the most favorable situation for receiving the tears. It serves, also, to 

 compress the lachrymal sac. 



4. OEBITAL EEGION (fig. 149). 



Levator Palpebras. Kectus Internus. 



Bectus Superior. Rectus Externus. 



Kectus Inferior. Obliquus Superior. 

 Obliquus Inferior. 



Dissection. To open the cavity of the orbit, the skull-cap and brain should be first removed ; 

 then saw through the frontal bone at the inner extremity of the supra-orbital ridge, and externally 

 at its junction with the malar. The thin roof of the orbit should then be comminuted by a few 

 slight blows with the hammer, and the superciliary portion of the frontal bone driven forwards 

 by a smart stroke ; but it must not be removed. The several fragments may then be detached, 

 when the periosteum of the orbit will be exposed : this being removed, together with the fat 

 which fills the cavity of the orbit, the several muscles of this region can be examined. To facili- 

 tate their dissection, the globe of the eye should be distended ; this may be effected by puncturing 

 the optic nerve near the eyeball, with a curved needle, and pushing it onwards into the globe. 

 Through this aperture the point of a blow-pipe should be inserted, and a little air forced into 

 the cavity of the eyeball ; then apply a ligature round the nerve, so as to prevent the air escaping. 

 The globe should now be drawn forwards, when the muscles will be put upon the stretch. 



The Levator Palpebrse Superioris is thin, flat, and triangular in shape. It 

 arises from the under surface of the lesser wing of the sphenoid, immediately in 



