ORBITAL REGION. 321 



ridge ; from whence 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 

 lachrymalia. Its fibres appear to be continuous with those of the palpebral 

 portion of the Orbicularis; it is occasionally very indistinct. 



Nerves. The Orbicularis Palpebrarum, Corrugator Supercilii, and Tensor 

 Tarsi are supplied by the facial nerve. 



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 Palpebrse 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 fore- 

 head. 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 lachry- 

 mal canals 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. OKBITAL BEGION. (Fig. 216.) 



Levator Palpebrra Superioris. Rectus Internus. 

 Rectus Superior. Rectus Externus. 



Rectus Inferior. Obliquus Superior. 



Obliquus Inferior. 



Dissection. To open the cavity of the orbit, remove the skullcap and brain; then saw through 

 the frontal bone at the inner extremity of the-supraorbital ridge, and externally at its junction 

 with the malar. Break in pieces the thin roof of the orbit by a few slight blows of the hammer 

 and take it away ; drive forward the superciliary portion of the frontal bone by a smart stroke, 

 but do not remove it, as that would destroy the pulley of the Obliquus Superior. When the 

 fragments are cleared away, 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. The dissection will be facilitated by distending the globe of the eye. In order to 

 effect this, puncture the optic nerve near the eyeball, with a curved needle, and push the needle 

 onwards into the globe ; insert the point of a blowpipe through this aperture, and force a little 

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

 escaping. The globe being now drawn forwards, 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 front of the optic foramen; and is inserted, by a broad aponeurosis, into the 

 upper border of the superior tarsal cartilage. At its origin, it is narrow and 

 tendinous; but soon becomes broad and fleshy, and finally terminates in a broad 

 aponeurosis. 



Relations. By its upper surface, with the frontal nerve and artery, the perios- 

 teum of the orbit; and, in front, with the inner surface of the broad tarsal 

 ligament. By its under surface, with the Superior Rectus ; and in the lid, with 

 the conjunctiva. A small branch of the third nerve enters its under surface. 



The Rectus Superior, the thinnest and narrowest of the four Recti, arises 

 from the upper margin of the optic foramen, beneath the Levator Palpebroe 



