412 



PRACTICAL ANATOMY. 



part of the bulb. The nerves are about twenty in number on each side. They 

 pass through the olfactory foramina in the cribriform plate of the ethmoid bone. 

 In their course through the foramina, the nerves are invested by a sheath of 

 dura mater. (Fig. 87.) The olfactory nerve filaments are distributed to the 

 mucous membrane of the upper and middle turbinated bones, and to a corre- 

 sponding part of the septum nasi. (Fig. 75.) 



Describe tJie optic nerve. 



This nerve is the special nerve of sight, being distributed solely to the eye- 

 ball. The commissure is the place on the sphenoid bone where the two sides 



ffulA 



Ot feretory filaments 



FIG. 286. FIRST CRANIAL NERVE, OLFACTORY. 



are connected. The optic nerve proper is between the commissure and the eye- 

 ball ; the optic tract is between the commissure and the brain. 



Describe the optic tract. 



It arises (Fig. 92) : (i) From the pulvinar of the optic thalamus ; (2) from 

 the geniculate body ; (3) from the upper quadrigeminal body. The tract crosses 

 the crus cerebri (Fig. 92), being closely attached thereto, and terminates in the 

 optic chiasma or commissure. The student will recall the fact that the optic 

 chiasma and the optic tracts assist the crura cerebri and pons Varolii in forming 

 the boundaries of the interpeduncular space. (Fig. 92.) 



Longitudinal Fibers- 

 Decussating Fibers 

 Intcrcerehral Fibers 

 Inter-retinal Fibers 



FIG. 287. SECOND CRANIAL NIRVK, Orru. 



Describe the optic ncri'c proper. 



This nerve extends from the chiasma to the eyeball. It leaves the cranium 

 by the optic foramen, in the sphenoid bone, in company with the ophthalmic 

 artery. The nerve has a cranial part and an orbital part ; the latter is flexuous, 

 to accommodate the movements of the eyeball, and is surrounded by ciliary 

 vessels and nerves. 



/// practical anatomy i^Iicrc do you find tJic artcria ccntralis retuuc / 



This must In- seen in a dissection of the contents of the orbit. (Fig. 103.) 

 You will find this artery piercing the under part ojf the nerve, and about midway 

 between the optic forair.en and the globe. 



