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tissue between the layers. The inner nose or nasal cavities are separated by a septum, which is seldom quite median and is covered in its lower two-thirds by thick, highly vascular mucous membrane composed of columnar ciliated epithelium with masses of acinous glands (see See also:

EPITHELIAL, ENDOTHELIAL

EPITHELIAL TISSUES) embedded in it, while in its upper part it is covered by the less vascular but more specialized olfactory membrane. Near the front of the lower part of the septum a slight opening into a See also:

SHORT, FRANCIS JOB (1857– )

short See also:

BLIND, MATHILDE (1841—1896)

blind See also:

TUBE (Lat. tuba)

tube, which runs upward and backward, may sometimes be found; this is the vestigial remnant of " Jacobson's See also:

ORGAN

organ," which will be noticed later. The supporting framework of the septum is made up of ethmoid above, vomer below, and the " septal cartilage " in front. The outer See also:

wall. of each nasal cavity is divided into three meatus by the overhanging turbinated 1. See also:

VESTIBULE (from Lat. vestibulum)

Vestibule. 6.

Opening of anterior ethmoidal cells. 2. Opening of antrum of Highmore. 7. Cut edge of See also:

SUPERIOR

superior turbinated bone. 3. See also:

HIATUS (Lat. for gaping, or gap)

Hiatus semilunaris. 8. Cut edge of See also:

MIDDLE

middle turbinated bone. 4. Bulla ethmoidalis. 9.

Pharyngeal orifice of Eustachian tube. 5. Agger See also:

NASI, JOSEPH (16th century)

nasi. between it and the roof known as the " recessus spheno-ethmoidalis," into the back of which the " sphenoidal See also:

air sinus " opens. Between the superior and middle turbinated bones is the " superior meatus," containing the openings of the " posterior ethmoidal air cells," while between the middle and inferior turbinateds is the "middle meatus," which is the largest of the three and contains a rounded See also:

ELEVATION

elevation known as the " bulls ethmoidalis." Above and behind this is often an opening for the "middle ethmoidal cells," while below and in front a deep sickle-shaped See also:

GUTTER (O. Fr. goutiere, mod. gouttiere, from Lat. gutta, drop)

gutter runs, the " hiatus semilunaris," which communicates above with the " frontal air sinus " and below with the opening into the " antrum of Highmore " or " maxillary antrum." So deep is this hiatus semilunaris that if, in the dead subject, See also:

WATER

water is poured into the frontal sinus it all passes into the "7 8 OLFACTORY SYSTEM bones (see fig. 2). Above the superior turbinated is a space the sphenoidal turbinated bone separates the nasal cavity from the sphenoidal sinus above, and below there is an opening into the naso-pharynx known as the " posterior nasal See also:

APERTURE (from Lat. aperire, to open)

aperture " or " choana." The mucous membrane of the outer wall is characteristic of the respiratory See also:

TRACT (from Lat. tractare, to treat of a matter, through Provencal tractat and Ital. trattato)

tract as high as the superior turbinated bone; it is ciliated all over and very vascular where it covers the inferior turbinated ; superficial to and above the superior turbinated the olfactory tract is reached and the specialized olfactory epithelium begins. See also:

EMBRYOLOGY

Embryology. In the third See also:

WEEK (from A.S. wicu, Germanic *wikon, probably=change, turn)

week of See also:

INTRA

intra-uterine See also:

LIFE

life two pits make their appear- ance on the under side of the front of the See also:

head, and are known as the olfactory or nasal pits; they are the first See also:

APPEARANCE (from Lat. apparere, to appear)

appearance of the true olfactory region of the nose, and some of their epithelial lining cells send off axons (see See also:

NERVOUS

NERVOUS SYSTEM) which arborize with the dendrites of the cells of the olfactory See also:

LOBE

lobe Opening of middle ethmoidal cells of the See also:

BRAIN (A.S. braegen)

brain and so See also:

FORM (Lat. forma)

form the olfactory Openings of posterior ethmoidal cells nerves (see J. Disse, Anat. Hefte, 1897; Recessus spheno•ethmoidalis also P. Anat.

See also:

Soc., J. Anat. and Phys., 1897, p. 12). Between the olfactory pits the broad median See also:

FRONTO, MARCUS CORNELIUS (c. A.D. 100–170)

fronto-nasal See also:

PROCESS

process grows down from the forehead region to form the dorsum of the nose (see fig. 3), and the anterior part of the nasal septum, while outside them the lateral nasal processes grow down, and later on meet the maxillary processes from the first visceral See also:

arch. In this way the nasal cavities are formed, but for some See also:

time they are separated from the mouth by a thin bucconasal membrane which eventually is broken through; after this the mouth and nose are one cavity until the formation of the See also:

PALATE (Lat. palatum, possibly from the root of pascere, to feed)

palate in the third See also:

month (see MOUTH AND SALIVARY GLANDS). In the third month Jacobson's organ may be seen as a well-marked tube lined with respiratory mucous membrane and See also:

RUNNING

running upward and back-See also:

ward, See also:

close to the septum, from its orifice, which is just above the foramen of Stensen in the anterior See also:

PALATINE (from Lat. palatium, a palace,)

palatine See also:

canal. In See also:

man it never has any connexion with the olfaotory membrane or olfactory nerves. Internally and below it is surrounded by a delicate See also:

SHEET

sheet of cartilage, which is distinct from that of the nasal septum. No explanation of the See also:

FUNCTION

function of Jacobson's organ in man is known, and it is probably entirely atavistic. At See also:

BIRTH (a word common in various forms to Teutonic languages from the root of the verb " to bear ")

birth the nasal cavities are very shallow from above downward, but they rapidly deepen till the See also:

AGE (Fr. age, through late Lat. aetaticum, from aetas)

age of See also:

PUBERTY (Lat. pubertas, from pubes, puber, mature, adult)

puberty. The See also:

EXTERNAL

external nose at birth projects very little from the See also:

PLANE

plane of the face except at the tip, the See also:

BUTTON (Fr. bouton, O. Fr. boton, apparently from the same root as bouter, to push)

button-like shape of which in babies is well known.

In the second and third See also:

YEAR

year the See also:

BRIDGE

bridge becomes more prominent, but after puberty the nasal bones tend to tilt upward at their lower ends to form the See also:

EMINENCE (Lat. eminentia)

eminence which is seen at its best in the See also:

ROMAN

Roman nose. (For further details see See also:

QUAIN, SIR RICHARD, BART

Quain's Anatomy, vol. i., See also:

LONDON

London, 1908.) Cut edge of inferior turbinated bone Bristle passed into opening of nasal duct Sphenoidal air-sinus antrum and none escapes through the nostrils until that cavity is full. The passage from the frontal sinus to the hiatus semilunaris is known as the " infundibulum," and into this open the " anterior ethmoidal cells," so that the antrum acts as a sink for the secretion of these cells and of the frontal sinus. Running downward and forward from the front of the middle turbinated bone is a curved See also:

ridge known as the " agger nasi," which forms the anterior boundary of a slightly depressed See also:

AREA

area called the " See also:

ATRIUM (either from ater, black, referring to the blackening of the walls from the smoke of the hearth, or from the Greek aiOpeov, open to the sky, or from an Etruscan town, Atria, where the style of building is supposed to have originated)

atrium." The " inferior meatus " is below the inferior turbinated bone, and, when that is lifted up, the valvular opening of the nasal duct (see See also:

EYE) is seen. In front of the inferior meatus there is a depression just above the nostril which is lined with skin instead of mucous membrane and from which short hairs grow; this is called the " vestibule." The roof of the nose is very narrow, and here the olfactory nerves pass in through the cribriform See also:

PLATE

plate. The See also:

FLOOR (from O. Eng. flor, a word common to many Teutonic languages, cf. Dutch vloer, and Ger. Flur, a field, in the feminine, and a floor, masculine)

floor is a See also:

GOOD, JOHN MASON (1764-1827)

good See also:

DEAL

deal wider so that a coronal See also:

section through each nasal cavity has roughly the appearance of a right-angled triangle. The anterior wall is formed by the nasal bones and the upper and lower lateral cartilages, while posteriorly See also:

COMPARATIVE

Comparative Anatomy. In See also:

AMPHIOXUS, or LANCELET

Amphioxus among the See also:

ACRANIA

Acrania there is a ciliated See also:

PIT (O. E. pytt, cognate with Du. put, Ger. Pfutze, &c., all ultimately adaptations of Lat. puteus, well, formed from root pu-, to cleanse, whence gurus, clean, pure)

pit above the anterior end of the central nervous system, which is probably a rudiment of an unpaired olfactory organ. In the See also:

CYCLOSTOMATA, or MARSIPOBRANCHII

Cyclostomata (lampreys and hags) the pit is at first ventral, but later becomes dorsal and shares a See also:

COMMON

common opening with the pituitary invagination. It furthermore becomes divided internally into two lateral halves. In fishes there are also two lateral pits, the nostrils of which open sometimes, as in the elasmobranchs (sharks and rays), on to the ventral See also:

SURFACE

surface of the snout, and sometimes, as in the higher fishes, on to the dorsal surface. Up to this See also:

STAGE (Fr. 6/age; from Lat. stare, to stand)

stage the olfactory See also:

ORGANS

organs are See also:

mere pits, but in the Dipnoi (mud-See also:

fish) an opening is established from them into the front of the roof of the mouth, and so they serve as respiratory passages as well as organs for the sense of smell.

In the higher See also:

AMPHIBIA

Amphibia the nasal organ becomes included in the skull and respiratory and olfactory parts are distinguished. In this class, too, turbinal ingrowths are found, aad the naso-lachrymal duct appears. In the lizards, among the Reptilia, the olfactory and respiratory parts are very distinct, the latter being lined only by stratified epithelium unconnected with the olfactory nerves. There is one true turbinal bone growing from the outer wall, and close to this is a large nasal gland. In crocodiles the hard palate is formed, and there is henceforward a considerable distance between the openings of the external and See also:

INTERNAL

internal See also:

NARES, SIR GEORGE STRONG (1831– )

nares. In this See also:

order, too (Crocodilia) air sinuses are first found extending from the olfactory cavities into the skull-bones. The birds' arrangement is very like that of the See also:

REPTILES (Lat. Reptilia, creeping things, from reptilis; ref ere, to creep; Gr. Ep7rety, whence the term " herpetology," for the science dealing with them)

reptiles; olfactory and respiratory See also:

chambers are See also:

PRESENT

present, and into the latter projects the true turbinal, though there is a pseudo-turbinal in the upper or olfactory chamber. In mammals the olfactory chamber of the nose is variously See also:

DEVELOPED

developed ; most of them are " macrosmatic," and have a large area of olfactory mucous membrane; some, like the See also:

SEALS

seals, See also:

WHALEBONE

whalebone whales, monkeys and man are microsmatic," while the toothed whales have the olfactory region practically suppressed in the adult, and are said to be " anosmatic." There are generally five turbinal bones in macrosmatic mammals, so that man has a reduced number. The lowest of the See also:

SERIES (a Latin word from serere, to join)

series or " maxillo-turbinal " is the See also:

EQUIVALENT

equivalent of the single true turbinal bone of birds and reptiles, and in most mammals is a See also:

double See also:

SCROLL

scroll, one Maxillary process Mandibular arch f / III From A. H. See also:

Young and A. See also:

Robinson, in Cunningham's Text-Book of Anatomy.

FIG. 3. I. Side view of the head of human embryo about 27 days old, showing the olfactory pit and the visceral See also:

ARCHES, COURT OF

arches and clefts (from His). II. Transverse section through the head of an embryo, showing the relation of the olfactory pits to the forebrain and to the roof of the stomatodaeal space. See also:

LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf turning upward and the other down. Jacobson's organ first appears in amphibians, where it is found as an anteroposterior gutter in the floor of the nasal cavity, sometimes being close to the septum, at other times far away, though the former position is the more See also:

PRIMITIVE

primitive. In reptiles the roof of the gutter closes in on each side, and a tube is formed lying below and internal to the nasal cavity, opening anteriorly into the mouth and ending by a blind extremity, posteriorly to which branches of the olfactory and trigeminal nerves are distributed. In the higher reptiles (crocodiles and chelonians) the organ is suppressed in the adult, and the same applies to birds; but in the lower mammals, especially the monotremes, it is very well developed, and is enclosed in a cartilaginous sheath, from which a turbinal process projects into its interior. In other mammals, with the exception of the See also:

Primates and perhaps the See also:

CHIROPTERA (Greek for " hand-wings ")

Chiroptera, the organ is quite distinct, though even in man, as has been shown, its presence can be demonstrated in the embryo. The See also:

SPECIAL

special opening through which it communicates with the mouth is the foramen of Stensen in the anterior palatine canal.

See J. Symington on the organ of Jacobson in the Ornithorynchus,'P. Zoo!. Soc. (1891), and in the See also:

KANGAROO

kangaroo, J. Anat. and Phys., vol. 26 (1891); also G. See also:

Eliot See also:

Smith on Jacobson's organ, Anatom. Anzeiger, xi. See also:

BAND

Band No. 6 (1895). For See also:

general literature on the comparative anatomy of the olfactory system up to 1906, see R.

Wiedersheim's Comparative Anatomy of Vertebrates, translated and adapted by W. N. See also:

Parker (London, 1907). (F. G.

End of Article: OLFACTORY SYSTEM

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