450 HISTORY OF THE HUMAN BODY 



tions and certain other details suggests more especially the 

 mammalian condition. The first and most striking change is 

 the loss of the special system supplying the lateral line sense- 

 organs, the entire equipment for which vanishes in amphibians 

 that become terrestrial and never reappears. This causes at 

 jfonce, among other changes to be considered later on, a loss 

 of three branches of the facial nerve, the superficial ophthalmic, 

 the buccal, and the external mandibular. There remain the 

 palatine, the internal mandibular and the motor element of 

 the hyo-mandibular, of which the first two become reduced in 

 size and fuse with Trigeminus elements, while the third loses 

 in one direction but more than compensates for it in another. 

 The palatine, under the name of N. petrosus superficialis major, 

 passes through the pterygoid \_Vidian~} canal (in Mammals) 

 and enters the spheno-palatine ganglion of the sympathetic 

 system, where it meets with fibers of the Fifth nerve, and con- 

 tinues under the name of palatinus major, usually considered as 

 a part of the Trigeminus. The internal mandibular, now 

 known as the chorda tympani, transverses the tympanic cavity, 

 running between malleus and incus. It leaves the middle ear 

 through the Glasserian fissure (in mammals) and blends with 

 the lingual branch of ramus mandibularis V., encountering in 

 its course the sub-maxillary ganglion (better, sub-mandibular) 

 of the sympathetic system. 



The explanation of these complicated relationships becomes 

 clear when we consider the history of the related parts. Mal- 

 leus and incus are primarily the condyle of the jaw and the 

 quadrate bone, respectively, and the branch in question runs 

 along the articulation between them. In the Mammalia these 

 osseous elements become drawn within the cavity of the 

 middle ear, where they undergo a transformation into auditory 

 ossicles; and the nerve, in order to preserve its original rela- 

 tionships, must follow them, thus producing a complicated 

 condition, easily explained by their morphological history, but 

 wholly inexplicable otherwise. Furthermore, with the in- 

 creased importance of the tongue, and more especially with 

 the development of the fleshy part of it in mammals, the orig- 



