960 



THE NERVOUS SYSTEM 



accumulated into a rounded bundle, the optic nerve. The nerve thus formed pierces 

 the chorioid and the sclerotic coats, and, at the back of the bulbus, enters the orbital 

 fat, in which it passes backwards and inwards to the optic foramen. After traversing 

 the foramen it enters the middle fossa of the cranium, and anastomoses with its 

 fellow from the opposite side, forming the optic chiasma. It may, therefore, for de- 

 scriptive purposes, be divided into four portions the intra-ocular, the Intro-orbital, 

 the intra-osseous, and the intra-cranial. The total length of the nerve varies from 

 forty-five to fifty millimetres. 



The intra-ocular part is rather less than one millimetre in length. It passes 

 backwards from the optic papilla through the chorioid and through the sclerotic. 

 As it passes through the latter coat of the bulbus oculi in many separate bundles, 

 the area it traverses has a cribriform appearance when the nerve is removed, and con- 

 sequently is known as the lamina cribrosa solera;. 



The intra-orbital part of the nerve emerges from the sclerotic about three milli- 

 metres below and to the median side of the posterior pole of the bulbus, and it is 



FIG. 699. NERVES OP THE NASAL CAVITY. 



NASAL BRANCH 

 OF ETH.VOI11AL OLFACTORY 

 FRONTAL SINUS SERVE NERVE PLE.Xl 



\ I 



XUS 



SUPERIOR NASAL CONCHA 

 SPHENOIDAL SINUS 



\*ft VIDIA N NER I 'E 

 S,*$j SPHENO-PALATIKE 

 5XOT~>r~ GANGLION 



*^- * ' PA LA TIXE NER fES 



ORIFICE OF EUSTAOHIAN 

 TUBE 



NASAL BRANCHES 



POSTERIOR 



PALATINE 

 ANTERIOR 



PALATINE 



MIDDLE PALATINE 



about thirty millimetres long. It passes backwards and medianwards, surrounded by 

 the posterior part of the fascia bulbi (Tenon's capsule) and by the orbital fat, to the 

 optic foramen. As it runs backwards it is in relation above with the naso-ciliary 

 (nasal) nerve and the ophthalmic artery which pass obliquely from behind and out- 

 side, forwards and inwards across the junction of its posterior and middle thirds, and 

 also with the superior ophthalmic vein, the superior rectus muscle, and the upper 

 branch of the oculo-motor nerve. Below it are the inferior rectus muscle, and the 

 inferior division of the oculo-motor nerve. To its outer side, near the posterior part 

 of the orbit, are the ophthalmic artery, the ciliary ganglion, the abducens nerve, and 

 the external rectus muscle. The anterior two-thirds of this portion of the optic 

 nerve are surrounded by the ciliary arteries and the ciliary nerves and it is pene- 

 trated on its medial and lower aspect by the central artery of the retina. As it 

 enters the optic foramen to become continuous with the intraosseous part, it is in 

 close relation with the ligaments of Lockwood and Zinn (annulus tendineus com- 

 munis) and with the four recti muscles which arise from them. 



The intra-osseous portion is from six to seven millimetres long. It lies be- 



