THE CRANIAL OR ENCEPHALIC NERVES. 823 



nerve ; it is usually through the medium of this root that the ophthalmic 

 ganglion communicates with the superior cervical ganglion, by means of a thin 

 tilament it receives from the cavernous plexus. 



The emergent filaments leave the anterior part of the ganglion, and arrange 

 themselves in a flexuous manner around the optic nerve to reach the sclerotica, 

 hearing the name of ciliary nerves. Some emanate directly from tiie palpebro- 

 nasal nerve, especially when the ganglion is rudimentary. Their number is 

 uncertain, though it is usually from live to eight. 



Reaching the sclerotica at the bottom of the eye, they traverse that membrane, 

 and pass between its inner surface and choroid coat to the ciliary circle (or 

 ligament), where each divides into two or three ramuscules that anastomose with 

 those of the adjacent ciliary nerves, and in this manner they form a circular 

 plexus. From the concavity of this nerve-circle arises a series of plexuous 

 divisions, which are spread over the iris, influencing its contractile property. 



•2. Spheno-palatine, or Meckel's Ganglion. — The largest of the cranial 

 ganglia, nothing is more variable than its arrangement. The following appears 

 to be the most constant : in raising the superior maxillary nerve in its course 

 across the space separating the orbital from the maxillary hiatus, we discover, 

 lying on the upper border of the spheno-palatine nerve, a long, grey-coloured 

 enlargement ; this is the ganglion we are about to describe. 



It is elongated and slender, iiTegularly fusiform, constricted at diiTerent 

 points of its extent and dilated in others ; it is not attached to the spheno- 

 palatine nerve by simple cellular adhesions or by some branches thro\\'n from one 

 cord to the other, but is intimately united to it by means of a most complicated 

 intercrossing of fibres, in such a way that the spheno-palatine ganghon really 

 forms part of the nerve of that name. 



Afferent branches. — It receives, posteriorly, the Vidian nerve — a composite 

 ramuscule which constitutes its motor root, and connects it with the superior 

 cervical ganglion. This nerve will be described with the facial, as that trunk 

 furnishes its principal portion. Its sensitive roots naturally come from the 

 spheno-palatine nerve ; they are as remarkable for their number as their volume, 

 and also enter the posterior part of the ganglion. 



Emergent bra?iches. — Four series of these are recognized : 



(1) A very numerous series which is detached at a right angle from the 

 superior border of the ganglion, and proceeds towards the ocular sheath. The 

 majority appear to be lost in that fibrous membrane, but we have seen some pass 

 through it, creep on the lower and inner wall of the orbit, and arrive at the 

 margin of the orbital foramen. There they were manifestly united to the other 

 filaments coming from the palpebro-nasal nerve, and formed a small plexus, the 

 divisions of which seemed destined to the ophthalmic vessels, and even to some of 

 the muscles of the eye — more especially the oblique ones. Among these divisions, 

 we have observed some which went to join the nerve of the membrana nictitans. 



(2) A second series proceeding from the opposite border, and establishing a 

 union between the ganglion and the spheno-palatine nerve, or passing to the 

 palatine nerves in a more or less complicated plexiform manner, to increase them. 



(8) A group arising from the anterior extremity and immediately passing to 

 the spheno-palatine nerve. 



(4) A last fasciculus detached from the posterior extremity, to enter the two 

 great supra-sphenoidal canals. 



Such is the usual arrangement of the spheno-palatine ganglion. We have 



