SPECIAL ANATOMY. 143 



outwards and becomes aponeurotic, is inserted into the 

 anterior paii; of the sclerotic between the abductor and 

 depressor ; it passes externally to the depressor. 



The structures contained within the orbit receive blood 

 through the ocular branches of the internal maxillary artery 

 and through the ophthalmic artery. The former we have 

 already noticed, and of these the most remarkable, which 

 we distinguish are the lateral nasal, taking a peculiar curve 

 through the bottom of the orbit, and then passing into 

 foramen orbitale internum, and the supra-orhital, which 

 runs directly to the foramen of the same name. Ciliary 

 arteries run from the internal maxillary to the eyeball. 

 The ophthalmic artery arises in the cranial cavity from the 

 anterior communicating or from the middle cerebral 

 artery. It passes through foramen lacerum orbitale in 

 company with several nerves, and on emerging from the 

 foramen gives off branches to the lachrymal gland, and to the 

 eyelids, also arteria centralis retinae, which gains the eye- 

 ball by passing through the centre of the optic nerve. 

 Three nerves arising from the base of the brain (nominally) 

 supply the muscles of the eyeball with motor power. 

 Motores oculorum or third cranial pair of nerves, arising 

 from the centre of the under surface of the crus cerebrum, 

 each nerve passes from the cranium through foramen 

 lacerum orbitale and then gives off fibres to all the muscles 

 except the abductor and the superior oblique (and the 

 external part of retractor). From this nerve also a branch 

 passes to the ophthalmic or lenticular ganglion, a small 

 collection of nerve cells found at the point where the third 

 nerve gives off fibres to the inferior oblique muscle. It 

 receives sensory fibres from the lateral nasal branch of the 

 ophthalmic division of the fifth, and sends ciliary branches 

 to the eyeball. The ophthalmic division of the fifth 

 cranial nerve, passing from the gasserian ganglion, 

 emerges from the cranium through foramen lacerum orbi- 

 tale, it then breaks up to supply the structures of the eye 

 and its appendages with common sensation. Among 

 others, giving off the supra-orbital and lateral nasal nerves, 

 which follow the course of the arteries of the same name. 

 The lateral nasal affords the sensory root of the ophthalmic 

 ganglion. The pathetic or fourth nerve arises from the 

 valve of Yieussens, which forms the anterior part of the roof 

 of the fourth ventricle of the brain. These are the 



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