236 Mammalia. 



fossa (on which rests the cartilaginous disc) from the remain- 

 ing part behind, which is formed by the Tympanic subdivision 

 of the Temporal bone. The rest of the course of this nerve 

 lies within the Ear : it leaves the trunk of the Facial while 

 within its canal, enters the back part of the tympanic cavity 

 through a short canal close to the membrane of the Tympanum, 

 and crosses this membrane and the handle of the Malleus to 

 gain the aperture above noted at the inner end of theGlasserian 

 fissure. Its after course, as we have seen, is downwards and 

 forwards under cover of the posterior belly of the External 

 Pterygoid, internal to the Auriculo- temporal and inferior 

 Dental nerve, to unite with the Gustatory nerve at an acute 

 angle : with this nerve it ascends, in close contact, to a point 

 about opposite the posterior molar teeth, then curves down- 

 wards and backwards to the sub-maxillary ganglion, and along 

 the course of the duct of the sub-maxillary gland to the 

 second factor of the ganglion near the gland, and there 

 it becomes too fine to trace its terminal twigs. 



!N^ext let him take the posterior belly of the External Ptery- 

 goid with the inner angle of the condyle of the jaio attached to it, 

 and pass it, beneath the internal maxillary artery , forwards between 

 the Buccal and Gustatory nerves^ in order to expose the junction 

 of the four great branches of the Inferior Maxillary sub- 

 division of the Trifacial, viz., the Buccal, Gustatory, Inferior 

 Dental, and Auriculo- Temporal : these may then be traced 

 up to the skull and cleaned ; and the united trunk noted to 

 perforate the skull at a point a little anterior and internal to 

 the site of the temporo-maxillary articulation. The Fora- 

 men thus arrived at, inasmuch as it transmits the third 

 or inferior division of the Trifacial, is homologous with the 

 so-called foramen ovale of the human skull. 



Dissection of Internal Pterygoid Nerve ; Eustachian 

 Tube ; and Otic Ganglion. Having thus two fixed points to 

 start from, vi%., the Chorda tympani and the united Inferior 



