252 HEAD AND NECK 



ciliary nerve. It leaves 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 forwards, under the dura mater, and 

 almost immediately 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. 30). 



Ganglion Ciliare (Fig. 97). 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 is given off by the naso-ciliary, and is called 

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

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

 goes to the inferior oblique muscle. The sympathetic root is 

 derived 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 

 five to seven in number. As they 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. They 

 form two groups, superior and inferior, and the lower nerves 

 are generally more numerous than the upper. 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 forwards along the medial 



