DISSECTION OF THE ORBIT 341 



the orbit by the anterior ethmoidal canal, and is conducted to 

 the interior of the cranium, in which it appears at the lateral 

 margin of the cribriform plate of the ethmoid. The canal 

 in which it runs can readily be opened up with the bone- 

 forceps to expose the nerve. Upon the cribriform plate it 

 turns anteriorly, under the dura mater, and almost immedi- 

 ately disappears, through a slit-like aperture at the side of the 

 crista galli, into the nasal cavity. There it gives internal 

 nasal branches to the mucous membrane, and is continued 

 downwards upon the posterior aspect of the nasal bone. 

 Finally, it emerges upon the face, as the external nasal nerve, 

 by passing between the lower margin of the nasal bone and 

 the lateral cartilage of the nose. Its terminal filaments have 

 been described already (p. 140). 



Ganglion Ciliare (Fig. 138). The ciliary ganglion is a 

 small quadrangular body, not much larger than the head 

 of a large pin. It is placed in the posterior part of the orbit, 

 between the optic nerve and the lateral rectus muscle, and 

 very commonly on the lateral side of the ophthalmic artery. 

 At its posterior border it receives its three roots ; whilst from 

 its anterior border the short ciliary nerves are given off. 



The sensory root comes from the naso-ciliary, and is called 

 the long root. The short or motor root is a short, stout trunk ; 

 it comes from the branch of the oculo-motor nerve which 

 goes to the inferior oblique muscle. The sympathetic root 

 comes from the internal carotid plexus, it joins the ganglion, 

 close to the entrance of the long root from the naso-ciliary 

 nerve. In some cases it joins the long root before it reaches 

 the ganglion. 



Nervi Ciliares Breves. The short ciliary nerves are from 

 four to six in number. They come off in two groups, superior 

 and inferior. The lower nerves are generally more numerous 

 than the upper. As these fine nerves pass along the optic 

 nerve they divide and thus increase in number ; at the back 

 of the eyeball from twelve to eighteen may be counted. 

 Finally they pierce the sclera by a series of apertures which 

 are placed around the entrance of the optic nerve. 



Arteria Ophthalmica. The ophthalmic artery is a branch 

 of the internal carotid. It accompanies the optic nerve 

 into the orbit through the optic foramen. At first it lies 

 below the optic nerve, but soon winds round its lateral side, 

 and, crossing above it, passes anteriorly along the medial 

 ii 22 a 



