812 MAMMALIA. 



respect, excepting that in the lower orders a remnant of the nictitating 

 membrane is still met with ; but it is of small dimensions, and unpro- 

 vided with muscles. 



(2381.) The lacrymal apparatus exists in all quadrupeds ; and the 

 lacrymal gland occupies the same situation as in Man, the tears being 

 poured on to the conjunctiva near the external canthus of the eyelids. 

 The lacrymal ducts, likewise, whereby the tears are conveyed into the 

 nose, so nearly resemble the human as to require no particular descrip- 

 tion. The carunculce lacrymales are also met with at the inner canthus 

 of the eyelids. In some quadrupeds, indeed, an additional gland exists, 

 called the glandula Harderi ; this is situated behind the internal angle 

 of the eye, and secretes a lubricating fluid, that is discharged beneath 

 the rudiment of the third or nictitating eyelid. 



(2382.) In Whales, as might be expected from their aquatic habits, 

 no vestige of a lacrymal apparatus is to be seen. 



(2383.) Behind the optic lobes of the encephalon the nervous centres, 

 from whence the other cerebral nerves take their origin, are so inti- 

 mately blended together that the anatomist is no longer able to distin- 

 guish them from each other. They form, in fact, the " medulla ob- 

 fangata" and are the commencement of that long series of sentient and 

 of motor ganglia that forms the spinal cord. 



(2384.) All the nerves derived from the medulla oblongata and from 

 the spinal cord are throughout the Mammiferous class exactly com- 

 parable to those met with in our own species, and therefore will require 

 but brief notice. 



(2385.) The third, fourth, and sixth pairs are destined to the muscles 

 of the eye, and their distribution is the same as in Man. 



(2386.) The fifth pair, or trigeminal nerves, consist of both motor 

 and sentient fasciculi, both of which are distributed to the different parts 

 of the face exactly as in the human subject, allowance of course being 

 made for the varying form of the jaws, and for the proportionate size of 

 the different organs connected with mastication. 



(2387.) The seventh, or facial nerve, as also the glosso-pharyngeal, 

 the pneumogastric, and the lingual, have the same origin and general 

 distribution throughout the whole class. 



(2388.) The eighth pair of nerves are here, as in all the Vertebrata, 

 devoted to the sense of hearing, which in the Mammifera attains its 

 highest development and perfection. The sensitive portion of the auditory 

 apparatus, or the internal ear, is now enclosed in the petrous portion of 

 the temporal bone, and imbedded in osseous substance of such stony 

 hardness that, except in very young subjects, it is by no means easy to 

 display its different parts. 



(2389.) As in Fishes and Reptiles, it consists of several membranous 

 chambers or canals, filled with a limpid fluid, over which the filaments of 

 the auditory nerve spread out. The whole apparatus, indeed, except in 



