THE CRANIAL OR ENCEPHALIC NERVES. 719 



from the palpebro-nasal nerve, especially when the ganglion is rudimentary. 

 Their number is uncertain, though it is usually from 5 to 8. 



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 ra- 

 muscules that anastomose with those of the adjacent ciliary nerves, and in 

 this manner form a circular plexus. From the concavity of this nervous 

 circle arises a series of plexuous divisions, which are spread over the iris, 

 whose contractile property is submitted to their influence. 



2. SPHENO-PALATINE, OR MECKEL'S GANGLION. The largest of the 

 cephalic ganglia, nothing is more variable than the disposition of this small 

 body. 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 

 constitutes the ganglion we are about to describe. 



It is elongated and slender, irregularly fusiform, constricted at different 

 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 thrown 

 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 ganglion really forms part of the nerve of that name. 



Afferent branches. It receives, posteriorly, the Vidian nerve, a com- 

 posite 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 branches. Four series of these are recognised : 



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 whose divisions 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 reinforce 

 them. 



3. 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 suprasphenoidal canals. 



Such is the most usual arrangement of the spheno-palatine ganglion. 

 We have found it divided into three small masses connected with each 

 other by numerous filaments of a deep grey colour, and free from all ad- 

 herences with the spheno-palatine nerve. The small posterior mass in this 

 case received the Vidian nerve and the sensitive roots from the fifth pair. 

 The distribution of the emergent branches was unaltered. 



