THE EYE AND ITS APPENDAGES. 



171 



or four in number. The last is called impar or azygos, being 

 situated in the median line of the coccyx, and constituting the termi- 

 nating ganglio7i of the sympathetic. 



SECTION VII. 

 ORGANS OF SENSE. 



NOSE. 



The nose consists of two portions, an external projection upon the 

 face, and an internal cavity. The external portion is formed by the 

 nasal processes of the superior maxillary bones, the nasal bones, and 

 by five cartilages, two of which are placed upon either side and one 

 in the middle. The cartilaginous septu7n is placed in the median 

 line f it is thick, flat, and triangular, uniting by its superior edge, 

 with the ethmoid, and by its inferior edge with 

 the vomer. Its anterior edge unites with the 

 lateral and alar cartilages. It frequently de- 

 viates from the median line. The lateral car- 

 tilages^ are triangular, one being placed on either 

 side, attached above and behind to the bone, in 

 front with the septum, and below with the alar 

 cartilage. The alar cartilages'* are two in 

 number ; they form the lower portion of the 

 nose, and the opening called the nostril. It is 

 an irregular, semi-elliptical cartilage, and has 

 a number of small pieces of cartilage attached 

 to it, by which the nostril is kept open. These 

 cartilages are held together by a fibrous tissue. 

 The skin which covers the nose is thick and 

 strong, and covered with numerous sebaceous 

 follicles, which are frequently recognised by 



their being discoloured. The hairs visible in the nostril are termed 

 vibrissa. 



The cavity of the nose is lined by a membrane called pituitary, or 

 Schneiclerian, which is thick, soft, and red, owing to its vascularity, 

 and largely supplied with nerves, being the seat of smell. It lines 

 the meatuses of the nose, and is continuous with the mucous mem- 

 brane of the mouth, lachrymal canal, Eustachian tube, and frontal 

 sinus. It is supplied by the first and fifth pairs of nerves. 



THE EYE AND ITS APPENDAGES. 



The eyeball is a sphere, of about one inch in diameter, antero- 

 posteriorly, and somewhat less transversely. It is surrounded 

 by a fibrous capsule, which is continuous with the sheath of the 

 optic nerve behind, and the cartilages of the eyelids in front. All 

 the muscles of the ball of the eye lie behind, and perforate it, in 

 order to be inserted into the sclerotic coat. 



