246 ELEMENTS OF MAMMALIAN ANATOMY 



the tongue. The fungiform are l)lunt papillae scattered sparsely 

 in the midst of the numerous filiform or pointed papillae (Fig. 

 62). The special organs of taste, known a.s tasle-biids, are very 

 numerous in the fungiform and vallate 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 glosso- 

 pharyngeal 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 con- 

 junctiva, 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 oculi (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 medial or inner canthus 

 are two minute apertures, the puncta lachrymalia, leading into 

 two short canals which unite to form the nasal duct. The 

 lachrymal canal, which forms the channel for this duct, is 

 clearly visible in the lachrymal bone of the dried skull. At 

 the medial canthus there is a prominent fold of mucous mem- 

 brane, the membrana nictitans, or plica semilunaris, which is 

 a rudimentary structure in the cat, but is found well developed 

 in birds which have the power of sweeping it rapidly across 

 the eyeball, thereby removing dust. 



On the inner surface of each lid are the large sebaceous 

 tarsal glands. The lachrymal gland lies in the dorso-lateral 

 region of the orbit, and its ducts open on the ventral surface 

 of the upper lid, whence the tears flow over the conjunctiva 

 ventrad to the puncta lachrymalia. The Harderian gland is 



