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 is distributed over the entire surface of 

 the body. 



THE NOSE AND NASAL FOSS.E. 



The organ of smell consists essentially of two parts: one exter- 

 nal, the nose ; the other internal, the nasal fosses. 



The nose is the triangular pyramid projecting from the centre of 

 the face, immediately above the upper lip. Superiorly, it is con- 

 nected 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 re- 

 ceived 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 (vibrissce), 

 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. Mu- 

 cous membrane. 6. Vessels and nerves. 



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

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

 separated from the fibro-cartilage. It is furnished with a number 

 of sebaceous follicles, which by their oily secretion, protect the ex- 

 tremity of the nose in excessive alternations of temperature. The 

 sebaceous matter 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 tire integument is firmly 

 compressed, the inspissated 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. 





