110 D. A. RHINEHART 



S. Nervus chorda tympani 



The chorda tympani arises from the ventral side of the facial 

 nerve along the posterior part of the upper wall of the tympanic 

 cavity between the origin of the nervus stapedius and the anas- 

 tomosis with the ramus auricularis vagi. It is formed by the 

 more ventral and smaller of the two bundles of fine fibers which 

 come from the interior of the geniculate ganglion and pass pe- 

 ripherally as a part of the facial stem (figs. 9, 10, 11, 12, and 13, 

 N.Ch.Ty.). It has been showni above that it contains fibers 

 which are processes of cells in the geniculate ganglion and others 

 which pass through the ganglion without interruption. 



In the mouse, soon after its origin, the chorda bends medially 

 and anteriorly and passes through a fissure-like opening into the 

 tympanic cavity. Here it extends anteriorly in a shallow groove 

 along the upper part of the lateral wall, and then along a groove 

 in a spicule of bone which projects into the cavity. At the apex 

 of this spicule the nerve crosses a small gap to reach the medial 

 surface of the head of the malleus, across which it passes lying 

 ventral to the attachment of the tendon of the tensor tympani 

 muscle. In the anterior part' of the cavity it passes along the 

 medial side of the anterior process of the malleus, accompanying 

 that process into the fissure between the tympanic and periotic 

 bones (petrotympanic fissure) through which it extends into the 

 infratemporal fossa. In the infratemporal fossa the chorda tym- 

 pani passes medially and ventrally posterior to the emerging 

 mandibular nerve. After a course of varying extent it joins the 

 posterior aspect of the lingual nerve. 



Just before joining the lingual there is usually an anastomosis 

 with a bundle of fibers from another source. This is, in a ma- 

 jority of my series, a small branch arising from the mandibular 

 nerve. In one series a branch from the auriculotemporal nerve 

 joins it; in another a branch from the lingual joins it, the two 

 then uniting with the lingual; in one series there is no anastomo- 

 sis of any sort. All of the branches which anastomose with the 

 chorda tympani are composed of fibers of larger size than those 

 in the chorda. ^\Tien followed centrally they become lost in 

 the trunk of the mandibular nerve. 



