THE NERVOUS SYSTEM. 233 



tongue, the soft palate, the pillars of the fauces, epi- 

 glottis, and part of the cheek. On the dorsum of the 

 tongue are seen four kinds of papillae the circumvallate, 

 the fungiform, the filiform, and flat. The circumvallate 

 papillae are from eight to twelve in number, forming two 

 sides of a triangle on the caudal portion of the dorsum 

 of the tongue. The fungiform are blunt papillae scattered 

 sparsely in the midst of the numerous filiform or pointed 

 papillae (Fig. 55). The special organs of taste, known 

 as taste-buds, are very numerous in the fungiform and 

 circumvallate papillae of most mammals, but in the cat 

 they are few and not well differentiated. These taste- 

 buds occur in many parts of the mucous membrane of 

 the mouth cavity, each being supplied with a branch 

 of the glossopharyngeal nerve. 



The Visual Organ.- -The special organ of sight is 

 the eye, which occupies the orbital cavity of the skull. 

 The ball of the eye is protected above and below by 

 extensions of skin called the eyelids or palpebrae, which 

 are lined with mucous membrane, a transparent layer 

 of which, known as the conjunctiva, extends over the 

 front of the eyeball between the two lids. The dorsal 

 lid is raised by the levator palpebrae muscle, which 

 has its origin in the occipitofrontalis muscle. A sphincter 

 muscle, the orbicularis palpebrarum, lies on the margin 

 of the lids, and by its contraction closes the eye. 



The point on either side where the two eyelids meet 

 is termed the canthus or angle. At the mesal or inner 

 canthus are two minute apertures, the puncta lachry- 

 malia, leading into two short canals which unite to 

 form the nasal duct. The lachrymal canal, w r hich forms 

 the channel for this duct, is clearly visible in the lach- 

 rymal bone of the dried skull. At the mesal canthus 

 there is a prominent fold of mucous membrane, the 



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