THE HEAD AND NECK. 145 



superior rectus to be inserted into the sclerotica. You will find its nerve, the fourth, 

 breaking up into a number of filaments on the ocular surface of the muscle. 



The nasal nerve crosses the optic nerve, passes under the superior rectus 

 muscle, then passes between the superior oblique muscle and the internal oblique 

 muscle. Here it gives off its infratrochlear branch to meet the supratrochlear 

 branch of the frontal nerve. These two are sensory nerves. The nerve leaves 

 the orbit by the anterior ethmoid foramen with the anterior ethmoidal artery. In 

 the cranial cavity it lies under the dura, on the cribriform plate of the ethmoid 

 bone. It passes through the nasal slit to the nasal fossae. In the nasal fossae it 



Superior reetus 

 FOURTH NERVE \ 



Lsvator palpsbree superioris 



Lachrymal and frontal vein __SjM|K (#^lL f^~ Su P erior oblique 



. d f ge e ovfA a P hen C oi U d 8 al fr fls n sur i e brOU8 ~ T^S*1^~ PT1C F RA ^'^ A * D * Eli ' ' E 

 Naso-ciliary of fifth nerve jlS*$_^ ~ Internal rectus 



SIXTH NERVED / \ 



' N Inferior reetus 



External reotus THIRD NER VE 



FIG. 101. DIAGRAMMATIC REPRESENTATION OF ORIGINS OF OCULAR MUSCLES AT THE APEX 



OF THE RIGHT ORBIT. 

 (After Schwalbe, slightly altered.) 



divides into branches : (i) Septal, to the mucous membrane of the septum ; (2) 

 turbinals, to the turbinated bones. A small twig from the latter passes between 

 the lower end of the nasal bone and its cartilage, and appears on the face as the 

 naso-lobular a nerve of sensation, of course, to the wing and tip of the nose. 



TABLE OF ORIGIN OF OCULAR MUSCLES. 

 NAME. ORIGIN. 



Levator palpebrae superioris, . Above optic foramen from lesser ala of sphenoid. 



Superior rectus, Upper margin of optic foramen. 



Inferior rectus, From ligament of Zinn. 



Internal rectus, From ligament of Zinn. 



External rectus, Upper head. Outer margin of optic foramen. 



External rectus, Lower head. From ligament of Zinn. 



Superior oblique, Above the optic foramen. 



Inferior oblique, Orbital plate of superior maxilla. 



The internal rectus and the inferior rectus may be brought into view by 

 cutting the optic nerve and pushing the eyeball and the fatty mass forward. 

 You will see these muscles taking their nerve-supply from the third nerve. 

 Trace each muscle to its insertion into the sclerotica. 



The inferior oblique muscle arises from the orbital plate of the superior 

 maxilla just external to the lower end of the lachrymal groove. It is inserted 

 into the sclerotica, on the outer surface, in such a way as to antagonize the 

 superior oblique muscle. Its nerve, the long branch of the third cranial, is of 

 large size, and gives to. the ciliary ganglion its motor root. 



The orbital fascia invests the muscles. It passes forward on the tendons. 

 In the vicinity of the globe it binds the tendons together by extending from one 

 to another, thus forming, posterior to the ball, a loose double capsule the 

 capsule of Tenon. This double layer forms a socket for the ball to move in. It 

 separates posteriorly the fatty contents of the orbit from the globe of the eye. 



Describe the Ophthalmic Artery (Fig. 103). It is a branch of the inter- 

 nal carotid artery. It enters the orbit by the optic foramen with the optic nerve. 

 It is attended by the ophthalmic vein, which leaves the orbit by the sphenoidal 



