206 THE HEAD AND NECK 



lateral to the termination of the external maxillary artery 

 (Stiles). The upper end of the sac is blind, but below it narrows 

 to form the naso-lacrimal duct, which opens into the inferior 

 meatus of the nose. This duct is about half an inch long, and 

 its lower end is protected by a fold of mucous membrane (the 

 plica lacrimalis). In cases of epiphora where a blockage of the 

 naso-lacrimal duct is suspected, a probe may be passed along it 

 from its upper end. The lower lid is everted, and the probe is 

 entered at the punctum and passed in for a short distance. It 

 is then passed medially along the duct into the lacrimal sac until 

 its medial wall is encountered. The hand is then elevated so 

 that the point of the probe is made to pass downwards and 

 slightly backwards and laterally into the nose. The direction 

 of the naso-lacrimal duct is indicated by a line joining the medial 

 palpebral commissure (inner canthus) to the interval between 

 the first molar and the second premolar tooth. 



The Orbit and Eyeball. The Fascia Bulbi (Capsule of 

 Tenon) is a layer of fascia which almost completely surrounds 

 the eyeball, and is continuous with the sheath of the optic 

 nerve behind. Anteriorly, it lies deep to the conjunctiva and 

 terminates at the corneo-scleral junction. The bellies of the 

 orbital muscles lie outside the fascia, but their tendons pierce 

 it to gain insertion into the sclera, and the fascia is prolonged 

 backwards upon them to fuse with the muscle sheaths. These 

 prolongations are particularly strong in relation to the lateral 

 and medial rectus muscles, and they are connected to the walls 

 of the orbit, an arrangement which checks lateral and medial 

 rotation of the eye (check ligaments}. They are connected to 

 one another by a thickened part of the fascia bulbi which lies 

 below the eye, forming the suspensory ligament of Lockwood. 

 It is this band, together with the orbital periosteum, which 

 supports the eyeball after excision of the maxilla (p. 198). 



The Muscles of the Orbit. The Levator Palpebrce Superioris 

 lies immediately under the orbital roof. It is supplied by the 

 oculo-motor nerve, and when that nerve is paralysed the con- 

 dition of ptosis results. The Superior Rectus rotates the eyeball 

 upwards and medially. It acts in unison with the Inferior 

 Oblique, which rotates the eyeball upwards and laterally. Both 

 are supplied by the oculo-motor nerve. The Inferior Rectus 

 rotates the eyeball downwards and medially, and acts in unison 

 with the Superior Oblique, which rotates it downwards and 

 laterally. The former is supplied by the oculo-motor and the 



