ORGANA SENSUUM ET INTEGU- 

 MENTUM COMMUNE. 



By ROBERT HOWDEN, M.B., F.R.S.E. 



Professor of Anatomy in the University of Durham. 



ORGANA SENSUUM. 



THE organs of the senses are derived from cells of the ectoderm and constitute the 

 apparatus by which man is made acquainted with his surroundings. 



Every sense organ consists of three parts : (a) a peripheral or receptive portion, 

 capable of responding to external stimuli, (6) an intermediate or conductive part, 

 along which the impulses are conveyed, and (c) a central or perceptive portion, where 

 the impulses are collected and transformed into sensations. The intermediate and 

 central parts have been described in the section on the Nervous System; the 

 peripheral parts form the subject matter of this chapter, and may be grouped under 

 two headings : (a) those connected with the special senses of smell, sight, hearing, 

 and taste, and located in the nose, eye, ear, and mouth, respectively; and (ft) 

 those of general sensations (pressure, heat, cold, pain, etc.), which are widely dis- 

 tributed throughout the body. 



ORGANON OLFACTUS. 



The nose is the peripheral olfactory organ and consists of the nasus externus, 

 which projects from the face, and the cavum nasi, which is divided by a vertical 

 septum into right and left cavities. 



Nasus Externus. The external nose forms a more or less triangular pyramid, 

 of which the upper angle is termed the root, and is usually separated from the fore- 

 head by a depression, while its base, directed downwards, is perforated by the nares 

 or nostrils. Its free angle is named the apex ; and the anterior border, joining 

 root and apex, is termed the dorsum ; the upper part of the dorsum is supported by 

 : the nasal bones, and is named the bridge. Each side of the nose forms an open 

 angle (naso-facial angle) with the cheek, and ends below in a mobile expanded 

 ( portion, the ala nasi, which forms the lateral boundary of the naris, and is limited 

 . above by a furrow, the alar sulcus. The skin of the nose is thin and movable 

 i over the root, but thick and adherent over the apex and alee, where it contains 

 ; numerous large sebaceous glands. 



The arterial supply of the external nose is derived from the external maxillary and ophthalmic 

 arteries, and its veins open into the anterior facial vein and communicate with the ophthalmic 

 i vein. Its principal lymph vessels follow the course of the anterior facial vein and open into the 

 submaxillary lymph glands. From the root of the nose one or two vessels run laterally in the 

 upper eyelid and end in the upper anterior auricular lymph glands, while a third group runs 

 below the orbit to the lower anterior auricular lymph glands. Its muscles are supplied by the 

 facial nerve, and the skin covering it is supplied by the infra-trochlear and naso- ciliary branches 

 of the ophthalmic nerve and the infra-orbital branch of the maxillary nerve. 



The external nose presents great variety as to its size and shape, and certain well-defined 

 I types, such as aquiline, Grecian, etc., are described. The relation which its breadth, measured 

 across the alae, bears to its length, measured from root to apex, is termed the nasal index, and is 

 expressed thus : 



greatest breadth x 100 



greatest length. 



799 



