552 CRANIAL NERVES. 



pin's head, situated at the back part of the orbit between the optic nerve and the 

 External rectus muscle, generally lying on the outer side of the ophthalmic artery. 

 It is inclosed in a quantity of loose fat, which makes its dissection somewhat 

 difficult. 



Its branches of communication, or its roots, are three, all of which enter its 

 posterior border. One, the long root, is derived from the nasal branch of the 

 ophthalmic, and joins its superior angle. Another branch, the short root, is a short 

 thick nerve, occasionally divided into two parts ; it is derived from that branch 

 of the third nerve which supplies the Inferior oblique muscle, and is connected 

 with the inferior angle of the ganglion. A third branch, the sympathetic root, is a 

 slender filament from the cavernous plexus of the sympathetic. This is occasion- 

 ally blended with the long root, and sometimes passes to the ganglion separately. 

 According to Tiedemann, this ganglion receives a filament of communication from 

 the spheno-palatine ganglion. 



Its branches of distribution are the short ciliary nerves. These consist of from 

 ten to twelve delicate filaments, which arise from the fore part of the ganglion in 

 two bundles, connected with its superior and inferior angles ; the upper bundle 

 consisting of four filaments, and the lower of six or seven. They run forwards 

 with the ciliary arteries in a wavy course, one set above and the other below the 

 optic nerve, pierce the sclerotic at the back part of the globe, pass forwards in 

 delicate grooves on its inner surface, and are distributed to the Ciliary muscle and 

 iris. A small filament is described by Tiedemann, penetrating the optic nerve 

 with the arteria centralis retina?. 



(2.) SPHENO-PALATINE GANGLION. 



The SPHENO-PALATINE GANGLION or MECKEL'S GANGLION (fig. 281), the largest 

 of the cranial ganglia, is deeply placed in the spheno-maxillary fossa, close to the 

 spheno-palatine foramen. It is triangular or heart-shaped in form, of a reddish- 

 gray color, and placed mainly behind the palatine branches of the superior maxil- 

 lary nerve, at the point where the sympathetic root joins the ganglion^ It conse- 

 quently does not involve those nerves which pass to the palate and nose. Like 

 other ganglia, it possesses a motor, a sensory, and a sympathetic root. Its motor 

 root is derived from the facial, through the Vidian ; its sensory root from the fifth ; 

 and its sympathetic root from the carotid plexus, through the Vidian. Its branches 

 are divisible into four groups ; ascending, which pass to the orbit ; descending, to 

 the palate ; internal, to the nose ; and posterior branches to the pharynx. 



The Ascending branches are two or three delicate filaments, which enter the orbit 

 by the spheno-maxillary fissure, and supply the periosteum. Arnold describes and 

 delineates these branches as descending to the optic nerve ; one, to the sixth nerve 

 (Bock) ; and one, to the ophthalmic ganglion (Tiedemann). 



The Descending or Palatine branches are distributed to the 1 roof of the mouth, 

 the soft palate, tonsil, and lining membrane of the nose. They are almost a direct 

 continuation of the spheno-palatine branches of the superior maxillary nerve, and 

 are three in number, anterior, middle, and posterior. 



The anterior or large palatine nerve descends through the posterior palatine 

 canal, emerges upon the hard palate, at the posterior palatine foramen, and passes 

 forwards through a groove in the hard palate, nearly as far as the incisor teeth. 

 It supplies the gums, the mucous membrane and glands of the hard palate, and com- 

 municates in front with the termination of the naso-palatine nerve. While in the 

 posterior palatine canal, it gives off inferior nasal branches, which enter the nose 

 through openings in the palate-bone,, and ramify over the middle meatus, and the 

 middle and inferior spongy bones; and, at its exit from the canal, a palatine 

 branch is distributed to both surfaces of the soft palate. 



The middle or external palatine nerve, descends in the same canal as the pre- 

 ceding, to the posterior palatine foramen, distributing branches to the uvula, 

 tonsil, and soft palate. It is occasionally wanting. 



