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CHAPTER IX. 

 ORGANS OF SENSE. 



THE organs of sense, the instruments by which the animal frame 

 is brought into relation with surrounding nature, are five in number. 

 Four of these organs are situated within the head, viz. the apparatus 

 of smell, sight, hearing, and taste, and the remaining organ, of touch, 

 is resident in the skin, and distributed over the surface of the body. 



THE NOSE AND NASAL FOSS.E. 



The organ of smell consists essentially of two parts : one external, 

 tlie nose; the other internal, the nasal fossae. 



The nose is the triangular pyramid projecting from the centre of the 

 face, immediately above the upper lip. Superiorly, it is connected 

 with the forehead, by means of a narrow bridge ; inferiorly, it presents 

 two openings, the nostrils, which overhang the mouth, and are so 

 constructed that the odour of all substances must be received by the 

 nose before they can be introduced within the lips. The septum 

 between the openings of the nostrils is called the columna. Their 

 entrance is guarded by a number of stiff hairs (vibrissae) which project 

 across the openings, and act as a filter in preventing the introduction 

 of foreign substances, such as dust or insects, with the current of air 

 intended for respiration. 



The anatomical elements of which the nose is composed are, 1, 

 Integument. 2. Muscles. 3. Bones. 4. Fibro-cartilages. 5. Mucous 

 membrane. 6. Vessels and nerves. 



1. The Integument forming the tip (lobulus) and wings (alee) of the 

 nose is extremely thick and dense, so as to be with difficulty separated 

 from the fibre-cartilage. It is furnished with an abundance of seba- 

 ceous follicles, which by their oily secretion, protect the extremity of 

 the nose in excessive alternations of temperature. The sebaceous mat- 

 ter of these follicles becomes of a dark colour upon the surface, from 

 the attraction of the carbonaceous matter floating in the atmosphere ; 

 hence the spotted appearance which the tip of the nose presents in 

 large cities. When the integument is firmly compressed, the inspis- 

 sated sebaceous secretion is squeezed out from the follicles, and, taking 

 the cylindrical form of their excretory ducts, has the appearance of 

 small white maggots with black heads. 



