Encyclopaedia of the medical sciences ... forming a portion of the Encyclopaedia Metropolitana.

Date:
1847
Catalogue details

Licence: Public Domain Mark

Credit: Encyclopaedia of the medical sciences ... forming a portion of the Encyclopaedia Metropolitana. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    62/590 (page 428)
    SECTION III. OF THE SENSES. Anatomy. The general properties and functions of the Brain ~j and Nerves having been already considered,* the Ana- tomy and appropriate or specific Physiology of the Or- gans of Sense remain to be treated of under the present head. The senses may be defined as those organs by which external impressions are received and conducted to the Sensorium ; each sense, therefore, consists of a recipient surface and propagating medium. To the constitution of a perfect organ the following essentials must be present:—1. A special nerve; 2. An appropriate stimulus from without; 8. A capacity on the part of the former (the nerve) to appreciate the specific influence of the latter (the stimulus). Thus it will be perceived that the Nerve is the fundamental part of the sense, whilst the so-called organ merely presents a surface for the extension of the nervous matter, and a mechanism more or less complex for the modification of external impressions. It is not difficult to trace the operation of appropriate impressions on the various Organs of Sense, but it is quite beyond the limit of our present knowledge to follow them further ; and all the theories which have been broached to throw light on this sub- ject amount to little else than idle speculation. Obser- vation and experiment have enabled the physiologist to isolate (or nearly so) those parts of the brain which are associated with the external senses (see Anatomy ok the Brain); but this knowledge affords him no clue to the intricate problem above alluded to. Before con- cluding these introductory observations, the reader should be reminded that what we denominate Sound and Light, Odours and Tastes, have no ab- stract existence : the conditions necessary for the pro- duction of these effects may exist, but the effects them- selves are recognized only in connexion with appropriate organs to receive and communicate the impressions: thus, no words can convey the idea of what light is to the blind; nor can the deaf man form an adequate notion of what is meant by sound. Lastly, it may be remarked that all impressions made on the Senses are more or less transient in themselves, i. e., the material effect does not long survive the cause. It is only when the mysterious boundary is passed, and impressions become acknowledged and associated by the immaterial part of our nature, that they assume a permanency which converts them into materials that constitute the fabric of all our knowledge. The Senses are five in number: they will be de- scribed in the order of enumeration ;—Smell, Taste, Touch, Hearing, and Sight. In each instance the de- scription of the mechanism of the organ will be suc- ceeded by that of its nervous and vascular organization, and its physiology. * 'Nervous System,—Structure and Physiology,' p. 151. 428 Organ of Smell.—The Nose, properly so called, Anatom constitutes but a small portion of the organ by which odours are perceived. It is more or less prominent and pyramidal in form, projecting from the face between and below the eyea and above the mouth It is com- posed of bones, cartilage, mucous membrane, and common integument The external aperture is divided, not always symmetrically, by a central cartilaginous septum. The back of the nose is formed by the junc- tion of the nasal bones above, and of the lateral carti- lages below : it is upon the development of these bones that the form of the organ is chiefly dependent.* The AIcp or wings constitute the lateral boundaries of the nostrils, and are prolonged into the lobe or extremity of the nose. These alar cartilages are two in number on each side, the superior being triangular and flattened, the inferior curved and convex externally. The Septum of the nose is formed by a fifth cartilage, which is tri- angular and flat, and continuous with the bony plate which divides the nostrils behind. It meets the alar cartilages below in the lobe, and is here covered by a thick fold of the common integument called the Co- lumnar which connects the tip of the nose to the upper lip. The lobe and columnaare moulded on a separate pair of cartilages. The Nostrils are a pair, oval in form, and bounded by the septum and columna internally, and by the alar cartilages externally. Their inner surface is furnished with strong hairs, which are of use to arrest the intro- duction of extraneous bodies during the act of inspira- tion. The Nasal Cavity presents an extended surface covered throughout by mucous membrane, and is in communication with several Siriuses which are likewise invested by productions of the same continuous mem- brane. The bones which constitute the nasal cavity are fourteen in number, of which four are single bones and five are pairs. A central partition divides this cavity into two portions: this septum is vertical and continuous with the anterior cartilaginous septum of the nostrils already alluded to. It consists of the vomer, joining before with the nasal plate of the ethmoid bone, below with the palate and superior maxillary bones, and above with the sphenoid. The lateral boundaries consist of the superior maxillary, palate, sphenoid, ethmoid, turbinated, and lachrymal bones; the roof being formed by the frontal, ethmoid, and sphenoid bones, and the floor by the palate and superior maxillary bones. Lastly, the circumference of the common posterior aperture is formed by the sphe- noid and palate bones: this outlet communicates, in * For the description of these and other bones to which it will be necessary to allude, the reader is referred to the ' Osseoui System.'