23 



CHAPTER v.— The Senses. 

 Sight appears to be the only sense which is well developed 

 in snakes, at least according to the conventional standard. 

 The scaly tegument can hardly be endowed with much 

 sensibility ; from their habit of swallowing food whole, it is 

 probable that their taste cannot be very delicate ; the nasal 

 cavities are but little provided with expansions of mucous 

 membrane ; and hearing cannot be an important sense con- 

 sidering the rudimentary state of the external ear. The 

 only remaining portion of this organ is a subcutaneous 

 capsule attached to the tympanic bone ; from this a long 

 slender bone, the stapes* conducts any vibrations of air 

 that may have penetrated the scales and muscles of the head 

 tx) the expansion of the auditory nerve. There is no external 

 orifice or tympanum. 



The eye is well developed in those snakes which live above 

 ground, although it varies in size and adaptation according 

 to the mode of life which it is destined to serve. It is 

 covered by a transparent layer of epidermis, which is cast 

 along with that of the general integument. It is unprovided 

 with eyelids, and is moved to a slight extent by the usual 

 muscles. The pupil varies in shape and size ; in most 

 snakes it is round, but it is elliptical and erect in the 

 LycodontidcB, the Pythonidoe, the Viperina and some of the 

 tree-snakes ; and in one family of the latter it is elliptical 

 and horizontal.*!' 



* The stapes is not readily found as it is a mere filament of elastic 

 bone projecting backwards towards the tympano-mandibular joint, 

 lying deep below the tympanic muscles. See Plate IV, fig. 6. 



t Of the three families of colubrine tree-snakes the Dendrophidoe 

 have a round pupil, the Dryiophidce a horizontally elliptical pupil, 

 the Dipsadidce an erect pupil. It is doubtful whether an elliptical 

 pupil is a sign of specially nocturnal habits. I may mention that Mr. 

 Gerard Krefi"t considers it is ; he calls the Australian Dendrophidoe 

 'the day tree-snakes' and the Dipsadidae 'the night tree-snakes.' 

 All snakes are more or less nocturnal animals. 



