Some branches both proceed from and join that portion of the nerve occupied by this gan glion petrosum. The most important of these is a small branch which proceeds from the ganglion into the tympanum (remus tympani cus nervi glosso-pharyngei ; nerve of Jacobson). The course and distribution of this branch were partly known to Schmiedal, Anderseh, Ehren ritter, and Comparetti,l1 but were more fully described by Jacobson.* The nervus tympa nicus enters a canal in the petrnus portion of the temporal bone, and there anastomoses with the Vidian and the carotid plexus of the sym pathetic. The orifice of this canal is placed between the jugular fossa and carotid canal, and external to the termination of the aqueduct of the cochlea. The ramus tympanicus is figured and described by Arnoldt as dividing into six filaments a filament to the fenestra rotunda ; 2. one to the fenestra ovalis ; 3. one which anastomoses with the sympathetic; 4. one distributed upon the Eustachian tube; 5. one, which he terms nervus petrosus profundus minor, anastomosing with the spheno-palatine ganglion ; 6. one, the nervus petrosus superfi cialis minor, which anastomoses with a branch from the otic ganglion or ganglion Arnold'. The nerve of Jacobson thus forms an anasto mosis among the glosso-pharyngeal, the second and third branches of the fifth pair, and the superior ganglion of the sympathetic. A small branch arises from the ganglion petrosum, as delineated by Arnold,§ which unites itself to the auricular branch of the par vagum.II Two other filaments are generally found con nected with that part of the trunk of the nerve occupied by the ganglion petrosum. These are a communicating twig between the ganglion petrosum and ganglion of the par vagum, and an anastomosing filament of the sympathetic. As these filaments are very minute, and lie in a dense fibrous sheath, they can only be displayed by an exceedingly careful dissection. The communicating filament between these two ganglia of the glosso-pharyngeal and par vagum is short, and passes directly from the one gan glion to the other. The communicating filament from the sympathetic conies from the superior cervical ganglion, mounts up between the trunks of the par vagum and glosso-pharyngeal, and divides into two portions,---one of these connecting itself to the ganglion petrosum, the other to the ganglion of the par vagum. The course and mode of termination of this com municating filament of the sympathetic is re presented differently by Wutzert from the de scription here given. I have adopted that given by Arnold," since it exactly agrees with my own dissections. Another branch has been described as arising from the ganglion petrosum immediately below the ramus tympanicus, and passing backwards behind the styloid process, to anastomose with the trunk of the facial after its exit from the stylo-mastoid foramen.* We here see that the anatomy of that portion of the glosso-pharyugeal nerve which lies within the foramen lacerum is very complicated, but it must be at the same time obvious that it em braces considerations of great interest in a phy siological point of view.
What the true nature of these two ganglia is, we cannot at present venture positively to de cide. I may mention, however, that Miillert states that he is satisfied, that the superior gan glion or ganglion jugulare resembles the Casse rian ganglion upon the trigeminus or fifth pair, and those upon the posterior roots of the spinal nerves, for while one portion of the nerve swells into a ganglion, the other passes by without assisting in its formation. On the other hand, he believes that the inferior gan glion differs decidedly from those upon the posterior roots of the spinal nerves, and resem bles the swelling which is occasionally found upon a nerve where it is joined by branches from the sympathetic. The ramus tympanicus, according to his view, belongs to the sympa thetic system of nerves.t On escaping from the foramen lacerum the glosso -pharyngeal occasionally forms direct anastomoses with the par vagum, spinal acces sory, and superior ganglion of the sympathetic ; at other times it only anastomoses with these through its branches.
Digastric and stylo-hyoid branch. — The origin of this branch is far from being regular. It frequently arises from the external side of the nerve soon after its exit from the foramen lace rum. It ramifies, name implies, in the digastric and stylo-hyoid muscles. The fila ments of this nerve anastomose in the substance of the digastric muscle with the digastric branch of the portio dura.§
Carotid branches are two or more in num ber, and pass from the convexity of the nerve or from some of its pharyngeal branches, and proceed upon the surface of the internal carotid, where they form a very evident anastomosis with the sympathetic, with the pharyngeal, and other branches of the par vagum, and assist in form ing the plexuses around the carotid arteries. They have been traced downwards for a consi derable extent, and found to anastomose with the superior and even with the middle cardiac nerves.
Pharyngeal branches.—The nerve next fur nishes the pharyngeal branches, which are from two to four in number. The largest of these proceed downwards, and their ramifications can be traced over the whole of the pharynx, but more particularly over its upper and middle portions. One or generally more of these pha ryngeal branches perforate the stylo-pharyngeus muscle, aml can be traced partly downwards up on the middle constrictor, partly upwards upon the superior constrictor and mucous membrane of the fauces, and also partly forwards upon the suffice of the tonsils. I have traced one of these pharyngeal branches through the posterior part of the hyo-glussus muscle into the mucous membrane at the side of the posterior part of the tongue. These pharyngeal branches, by their anastomoses with the pharyngeal branches of the par vaguni and pharyngeal branches of the sympathetic, form what is called the pha ryngeal plexus of nerves.* A distinct swelling is frequently found over the internal carotid artery, formed by the confluence of the princi pal pharyngeal branches of the glosso-pharyn geus, of the superior pharyngeal branch of the par vagum, and the pharyngeal branches of the superior ganglion of the sympathetic. This swelling varies considerably in size and appear ance. Huber,- describes a small ganglion in the pharyngeal plexus. Haase/ shortly de scribes this swelling as a gangliform enlarge ment. Wrisberg6 states that a ganglion, of the size of the ophthalmic, is placed at the conflu ence of these nerves. Scarpall describes and figures it as a gangliform plexus more particu larly connected with the pharyngeal branch of the par vagum. Wutzer5 states that he has been unable to detect this pharyngeal ganglion. Kilian" and Amold,-H- but more particularly Kilian, figure it as a plexus. Though I would not deny the occasional existence of a small ganglion in this region, yet I believe it will be found that this swelling is generally formed by the cellular tissue binding together these branches as they anastomose with and cross each other4t Lingual branches.—After the trunk of the nerve has furnished the pharyngeal branches, it sends off from its concave side some small twigs upon the surface of the tonsils. It then forms the lingual portion of the nerve, passes into the base of the tongue below the stylo glossus and posterior margin of the hyo-glossus muscle, where it divides into three or four branches. The superior of these is principally distributed upon the posterior part of the sides of the tongue, and sends some twigs backwards upon the palato-glossus muscle and mucous membrane of the fauces, where they anastomose with the other tonsillitic twigs. The middle part of the termination of the nerve passes through the lingualis and hyo-glossus muscles to reach the mucous membrane and papillw at the side of the base of the tongue. The re minder of the nerve perforates the genio-hyo glossus to reach the mucous membrane and papillae in the middle of the base of the tongue. The distribution of these twigs is confined to the mucous surface at the base of the tongue, and do not extend beyond au inch in front of the foramen cceeum. They pass through the muscles of the tongue without giving any fila ments to them.* Tonsillitis twigs.—The different twigs of this nerve which we have described as passing to the tonsils, form an intricate plexus, posterior to and around these bodies, which has been called the eireulus tonsillaris. These tonsillitic twigs are ultimately intermixed with the as cending filaments of the pharyngeal branch of the par vagum, and pass in considerable num bers to the isthmus of the fauces and soft palate. They anastomose also with the pos terior palatine branches of the second branch of the fifth pair, and, according to Wrisberg,t with a filament from the third branch of the fifth.