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Sao Proceedings of the Royal Society of Medicine és Does

Section of Odontology President—H. T. RoPer-Harz, MB. MDS.

[October 23, 1944]

Jacobson’s Organ

PRESIDENT'S ADDRESS By H. T. Roper-Hall, M.B., M.DS., M.R.CS. L.DS. (From the Department of Anatomy, University of Birmingham)

Jacogsow’s organ (the vomeronasal organ) was fully described by Jacobson (a Danish anatomist) in 1811; although Ruysch, in 1703, showed interest in it.

It is a paired structure, lying on each side of the nasal septum in the anterior part of the nose, just above the palate and varying in size from rudimentary to large according to the animal; it exists completely in human intra-uterine life, is rudimentary in adult man and other microsomatic animals, but is always well developed and functioning in the macrosomatic animals (Lenhossek, 1912).

The organ is tubular and consists in humans of a small opening on the nasal wall which communicates by means of a short tubular portion with the body; both entrance and interior of the organ are lined with cylindrical and ciliated epithelial cells of special sensory type; its general structure is similar in most animals, but there are important variations in anatomy. Always present and usually surrounding the organ is a tube of cartilage which differs in its shape and relationship in various animals.

There are three general anatomical arrangements of its duct: (a) As in man, monkey, &c.; with the anterior opening on the nasal septum. (b) As in horse, camel, pig, &c.; within the upper part of the incisive canal. (c) As in ox, &c., and some reptiles—on the anterior part of the palate just within the orifice of the incisive canal.

The arrangements (b and c) ensure a direct relationship between the mouth and Jacobson’s organ.

From the human dental point of view Jacobson’s organ is interesting as it lies closely above the incisive canal and incisor teeth, and because it has been asserted that mid-line cysts of the premaxilla may arise from aberration of its vestiges.


In humans, Jacobson’s organ develops at a very early age in embryonic life (8 or 9 mm.) in the primitive nasal cavity, on the medial side of the olfactory pit, which corresponds to the nasal septum.

It is first a shallow depression which in embryos of larger size is gradually transformed into a groove directed backwards, and afterwards becomes gradually closed from behind forwards, and only the anterior end remains open (see later description of 12-5 mm. stage).

In early human embryÿos this epithelial tube has a fairly wide communication with the pasal cavity, and it is comparatively long; e.g. according to Paulet (1907) the length of Jacobson’s organ in a 138 mm. human embryo is 0-35 mm. (length of groove and tube in 12-5 mm. embryo is 0-220 mm.). Brandt (1938) offers some useful observations on the calculation of the size of Jacobson’s organ.


The organ (in humans) consists of a pair of epithelial, elongated sacs enclosed in a cartilaginous capsule situated on the nasal septum and extending along it above the incisive canal; it is a narrow canal in the epithelium of the nasal septum 5 to 7 mm. long and directed horizontally backwards about 10 mm. above the floor of the nose, and opening anteriorly above the nasal spine.

An illustration is to be found in Ruysch and Sômmering (Franke).

Jacogson’s CARTILAGE

Each Jacobson’s organ is partially or entirely covered by a fine cartilaginous protective lamella; this cartilage puckers the mucous membrane of the nasal septum and the resulting bulge helps to locate the organ (Lenhossek, 1912).

These cartilages are variously described as the vomerine cartilage of Huschke; the accessory nasal cartilages of Sappey; the ploughshare cartilages of Jacobson; paraseptal

Nov.—ODont. 1 42 Proceedings of the Royal Society of Medicine 2

cartilages of Tyurgat or recurrent cartilages of Parker; they should not be mistaken for Jacobson’s organ itself. Franke (1921) proves that they are the same structures in man as in other animals. |

These cartilages (in humans) far outstrip in length the remains of the organ of Jacobson on both sides, and at the anterior end run out into many spurs, but they are undoubtedly the homologues of the cartilages which enclose the organ of Jacobson (Kôlliker, see Franke).

Weber (1904) says “Jacobson’s cartilage detaches itself from the floor of the cartilaginous nasal capsule at the side of the septum; it loses its junction with the posterior part of the capsule in Marsupials (Teydel), but in mammals the anterior part usually remains in contact with the septum; it thus appears to rise from the anterior part of the septum and to extend free backwards”.

Hamlin (1930) suggests that Jacobson's cartilage has two actions; one like the thoracic wall to prevent collapse when internal pressure is reduced and the contents expelled, and a second to facilitate a rise in internal pressure by preventing expansion of the organ at the time this pressure is being developed, thus favouring a complete ejection of its contents.

Nerve supplyThe nerve supply is derived from at least threc sources: olfactory, trigeminal, and the sympathetic system.

Minett (1925-26) says that in the horse the nerve supply is from the olfactory and sphenopalatine nerves.

Olfactory filaments have been observed by Read (1908), Milne Dickie (1914), Franke (1921), Denker and Kahler (1925), and Hamlin (1930); fifth cranial (trigeminal) nerve elements by Franke (1921), Kôülliker (see Franke), and Parker (1922); sympathetic elements by Keith (1933).

Denker and Kahler (1925) say that the organ is supplied by the terminal nerve, the same sensory nerve which supplies the organ of smell in fishes, and Buchanan (1916) states that in ruminants there is a direct nerve supply to the organ from Meckel’s ganglion.

Function—Jacobson’s organ appears to have no function in man, but in other animals it assists in the selection and recognition of suitable foods and acts as an important supplementary organ of taste and smell. Animals have patent incisive canals and thus juices and odours have free access to Jacobson’s organ (Keith, 1933).

Aïthough it is joined by filaments of the olfactory nerve it can scarcely be supposed that the organ has merely the same function as the olfactory area itself; the usual theory is that it represents an accessory organ of smell; it is rather unlikely that the inspired air reaches its special sensory cells, because in several animals the organ joins the oral cavity. ‘

According to Carlier, the organ helps in touch. Cuvier says it is an organ of smell and helps animals to tell which foods are poisonous; Gratiolet that it is important in detecting sexual smells; Carlier that it enables animals to acquire a notion as to what objects surround them, and Hamlin (1930) that its function may be to distinguish whole- some from harmful substances.

Jacobson believed it to be an organ of secretion; Kôlliker, that it secretes substances which have an influence on the specific nerves and enables the organism to be aware of the constitution of its own secretions.

Parker (1922) quotes Henning; the function of Jacobson’s organ has to do with water- olfaction as contrasted with air-olfaction.

Klein (1880) says it is an accessory organ of smell especially as it is so well developed in animals and absent or rudimentary in man. Animals possess the sense of smell to such a degree that humans can hardly have a true conception of its nature, and Pearlman says Jacobson’s organ is used by animals in “tracking” by smell.

As the organ is supplied by the same sensory nerve, the terminal nerve, which supplies the organ of smell in fishes, Broman is of opinion that the vomeronasal organ is the old water-organ of smell of the vertebrates adapted for terrestrial life.

Experimental proofs.—The contents can be expelled from Jacobson’s organ in a freshly killed calf bv pressure of the finger from bchind forwards when under water

Hamilin (1930) injected stain into the nose during life and killed the animal immediately, but found no colour in Jacohson’s organ. He proves that blood-pressure is the agent for emptying Jacobson’s organ. He further shows that air and liquid are forced out of Jacobson’s organ by increasing the blood-pressure by means of adrenalin, and conversely that liquid is drawn into Jacobson’s organ when the blood-pressure falls following the disappearance of the effects of adrenalin. .

Teydel found glandular secretions in the cavity of the organ, never air, and believes that it is only by the presence of this liquid that percention takes place: Broman (1927) proved bv morphological and experimental researches that the organ always contains a serous fluid which can be sucked from the nasal or oral cavity and that some mechanism 3 Section of Odontology 43

exists which closes the incisive canal when desirable; he concludes that the organ is an accessory organ of smell and that scents come to it in a serous liquid.

In view of the powerful connexion between the olfactory receptors and the subcortical centres which exist in animals in contrast to man, Milstein (1929) concludes that odour as represented by Jacobson’s organ must be connected intimately to the subcortical centres of sexual life and with other important centres (e.g. feeding).


(a) Comparative.—Jacobson’s organ exists extensively among vertebrates, and where it is absent, there are often embryonic rudiments.

This special area of the olfactory organ is highly developed in all herbivora, in which the incisive canals are widely open and thus the juices and odours of the mouth have free access to the organ; the incisive canal may be considered the original connexion of the primitive choanæ (Parker).

Fishes.—These have an olfactory organ of a double character which may be the fore- runner of Jacobson’s organ; in elasmobranchs a supplementary olfactory organ arises in connexion with each nasal passage and thus with the mouth (Neal and Rand).

Amphibia—McCotter (1917) says that the vomeronasal organ in frog is a cup-shaped structure that lies at the medial extremity of the inferior nasal chamber and communicates directly with it laterally.

Reptiles and birds.—In snakes and lizards the organ, which opens in the moutbh, is a finer sense organ than the olfactory organ proper and is clearly differentiated from the true organ of smell (Pearlman) (Symington, 1891). There is in birds a little recess in the nasal cavity which would correspond to Jacobson’s organ of the mammals. The organ was thought to be absent in reptiles until Howes (1891) discovered a pair of carti- lages in the anterior part of the nasal cavity which he thinks may be the cartilaginous sac of Jacobson’s organ; he concludes that the accepted principles of morphology forbid our looking upon Jacobson’s organ of reptiles and mammals as in any way distinct; Corning states that Jacobson’s organ in reptiles achieves a high degree of development; Pearson (1921) examined a late fœtus of Lygosoma species 4:8 mm. in length and found Jacobson’s organ present within its cartilage.

Monotremata.—Symington (1891) discussing Ornithorhynchus says that a bristle passed from the mouth into the incisive canal enters a cavity which extends backwards for some distance in relation to the nasal septum; this is Jacobson’s organ which is partly surrounded by a cartilaginous tube continuous with the floor of the nose. Symington thinks that Jacobson’s organ attains its highest development in Prototheria; he states that in all mammals so far investigated the opening is anterior to the cavity of the organ, but in Ornithorhynchus Jacobson’s organ extends forwards from the orifice as well as backwards.

T'ypical mammals.—In the Horse the nasal opening of Jacobson’s organ is just within the incisive canal (Minett). Camel, opens in top of incisive canal (Minett). Ox, 8 or 9 cm. long, opens within incisive canal; near nose or near palate according to breed (Minett). Pig, 2 to 3 cm. long, opens in incisive canal close to palate (Minett).

Morphological.—The organ is present with its cartilage in hyrax, and Broom (1898) suggests that this organ may prove to be a very useful study of affinities between hvyrax and rodents; he says the snout of hyrax is not of mammalian form and the palate is something like that of wombat and other Marsupials, but from his observations of Jacob- son’s organ Broom concludes that hyrax is similar to the Ungulata and nearest to sheep and ox.

From the above notes the conclusion is justified that Jacobson’s organ is widespread throughout all vertebrates.

(b) Human.—In man the organ is found some distance above the palate and opens directly into the nose.

Watson-Williams (1910) says that although a small tubular recess, corresponding with the situation of Jacobson’s organ has been stated to occur occasionally in adult man, he has never met with anything of the kind; on the other hand, Browne (1899) says Jacobson’s organ can be demonstrated in man about 1:5, but is of vestigial interest only; he quotes Kôlliker—average situation is 85 mm. above floor of nose and 24 mm. from junction of membranous septum and lip.

Franke says that Jacobson’s organ in the adult is 5 to 7 mm. long and about 10 mm. above floor of nose, opening anteriorly above the nasal spine.

Keith (“Human Embryology and Merphology”, 1933) has an illustration on page 228 showing its relation to the incisive canal; he states that in the human fœtus the organ is at its maximum at the fifth month and afterwards usually only vestigial. He also shows (1909 Edition, fig. 13) the preparation No. 169 in the Royal College of Surgeons’

Nov.—ODoxT. 2 44 Proceedings of the Royal Society of Medicine 4

collection, of the nose of a newborn child prepared by Mr. Shattock to show the normal development of Jacobson’s organ.

Noyes (1934) found Jacobson’s organ present in ten newborn infants; Kôlliker and others have shown that it is always present in the fœtus, often in voung children, and occasionally in adult man. > ‘

The organ nearly disappears in the higher mammals, and what is left of Jacobson’s organ in man, enters into the formation of the incisive canal (Neal and Rand).

There has been some controversy as to whether the structure seen in man, in various stages of development, is, in fact, the same anatomical entity as that found in the same region in many animals; this is quite understandable in view of the varied anatomical arrangements already mentioned, and discussed under heading “Comparative”.

According to Gegenbaur, the organ of Jacobson has not yet been demonstrated in man (Franke, 1921) but Wiedersheim believes that the progenitors of man must have possessed an organ of Jacobson, since the existence of Jacobson’s cartilage is evidence that they did so (Franke). This is now the generally accepted opimon.

‘ Pathological importance.—As is the case with other vestigial remnants, Jacobson’s organ is occasionally the site of pathological changes. Corning states that, in man, degeneration of Jacobson’s organ commences during the fourth month of life. Kôlliker (see Franke) is of the opinion that the lumen of the organ may be obliterated by excessive epithelial growth and that calcareous material may be dcposited in its walls.

L. Browne (1899) says that Jacobson’s organ predisposes to inflammation as it is a blind sac and favours accumulation of bacteria. Jacobson’s organ is of clinical interest as it corresponds with the seat of certain morbid changes: perforating ulcers and neuritic lesions, as seen in lupus, typhoid, leprosy and typhus.

Peter (see Franke) expresses the view that its disappearance in childhood is a result of the multiple inflammations which occurs in the nasal cavity.

It is also stated that exostoses of the nasal septum are due to hypertrophy of Jacobson’s organ; such exostoses occur only in this region, but although Jacobson’s organ is large and active in childhood, exostoses of this type occur only in adults; on the contrary, Onodi, suggests that they are due to Jacobson’s cartilage; he is supported by Franke (1921) who suggests that thickening of the septum in this area may be due to a thickening of the spur of the septal cartilage at the edge of the vomer (which is closely associated with Jacobson’s cartilage). Mihalcovics concludes that the organ can only be considered as a rudiment when present, and not as a defect when it js absent (Denker and Kahler, 1925).

The present writer (with Brandt, 1940) described a cyst in the posterior portion of Jacob- son’s organ in a human fœtus of 124 mm. (80 mm. cr.l.). As this part of Jacobson’s organ lies above the nasal opening of the incisive canal it is possible that increase in size of the cyst might be downward into the lumen of the canal and cause a cyst of the latter. This is one of the suggested explanations of cysts in this region.


During the investigation which preceded the writing of this paper dissections were made as follows:

Human, 3 (Jacobson’s organ found in one).

Monkeys, 4; sheep, 9; pigs, 7; cows, 5; calves, 4 (Jacobson’s organ found in all).

The writer acknowledges the fact that strictly scientifically these specimens are listed in the reverse order, but the importance of the findings in man and monkey appears to justify this departure for the special purpose of this paper.

Human—Twenty adult specimens were examined (visually only) for Jacobson’s organ without success. Three specimens were dissected thoroughly with the result that Jacobson’s organ was found in one specimen. L

Human specimen No. 3.—Jacobson's organ and cartilage were present and incisive canal was patent. | |

Description.—This specimen shows bilateral Jacobson’s organ, neither of which was patent nor could an ostium be found; both Jacobson's organs were covered by well- defined cartilage 1 cm. in length; length of the organ was 0-8 cm., width was 0:2 cm.; Jacobson’s organ was firmly attached to the mucous membrane anteriorly; the relationship to the incisive canal is shown in diagrams. The impression gained was that a cyst of Jacobson’s organ could not easily bulge into the canal. |

The centre of Jacobson’s organ is 1 cm. above the nasal orifice of the incisive canal, and the blood-vessels pass beneath it.

Laterally.—On removing the mucous membrane of the nasal septum about 1 cm. above the floor of the nose a small elongated cartilaginous mass was found lying antero- posteriorly practically parallel with the palate. ÿ Section of Odontology 45

From above.—When viewed from above it was seen that the oïgan lies above the incisive canal-—one-third of the organ anterior to the canal and two-thirds posterior. Monkeys (Rhesus).—Four specimens were dissected-—two young and two older specimens.

sn NAL

Frd0R 0 Was a LÉ OT Pi D m ° — /TAxILLA --M,or ROSES FACE. F ZE G FIG. 1. FIG. 2.

FIG. 1.—Human. From above (nasal septum bent slightly away from centre) showing Jacobson’s organ. FIG. 2.—Monkey (rhesus). Showing Jacobson’s organ. \

In an adult specimen Jacobson’s organ was found on both sides. The organ is placed high up on the lateral surface of the septal cartilage. It is pear-shaped, higher up the septum than in man, and lies at approximately an angle of 30° to the floor of the nose. It is noteworthy that the organ is placed so high as compared. with humans and other animals. In all specimens each Jacobson’s organ opened by a single orifice just within the anterior nares. -

Sheep Nine specimens were dissected. ‘

Jacobson’s organ passes nearly horizontally to the soft palate to the floor of the nasal cavity through the anterior-lateral part of the incisive canal where the orifice of the organ opens; medially are the naso-palatine nerves and greater palatine artery.

Composition and constitution.—The organ lies in a fibrous cartilaginous tube about 0-5 cm. in external diameter; the internal diameter being about 2 mm.; mucous membrane lining shaped like a test tube with a concave upper border following the lower border of the premaxilla. ‘

Size.—The length is usually described as from 2-5 to 4 cm. long and this was the case with all specimens dissected except one in which the length of the organ (including orifice) was 6 cm. with Jacobson’s cartilage another 1 cm. in length.

Jacobson’s cartilage lies within the shallow groove of the cartilaginous nasal septum with a thin layer of fibrous tissue between; it covers Jacobson’s organ from end to end, being somewhat thicker at its lower surface and accompanies the orifice of the organ to its opening, completely surrounding and protecting it, just within the incisive canal.

Pig (seven specimens).—Jacobson’s organ lies parallel to the floor of the nose and the palate and runs forward to the incisive canal where it opens a short distance within the

FIG. 3. FIG. 4. FIG. 3.—Sheep. Showing orifice of Jacobson’s organ high up in incisive canal. FIG. 4—Pig. Showing relationship to incisive canal. 46 Proceedings of the Royal Society of Medicine 6

canal with a small rounded tube-like opening in approximately the same plane as that of the organ.

Jacobson’s cartilage covers it completely above and within the canal, anteriorly there is a layer of “erectile” tissue at the region where the organ enters the canal.

At its anterior end Jacobson's cartilage becomes attached to the septal cartilage which flows with it within the incisive canal to the orifice of the organ, i.e. cartilage surrounds the organ to its orifice. The organ and its cartilage lie free at its posterior end—merely lying in a groove at the lower part of the nasal septum.

The anterior orifice of the organ lies at the level of the middle of the second incisor tooth, at a distance above the palatal orifice of the incisive canal. The canal is similar in angle and layout to that of the sheep.

Size of the organ: Old pig.—Length of organ 5 cm. Cartilage is 1 cm. longer. Organ is 2 to 3 mm. at widest. Young pig.—-Length of organ 3-5 cm. Cartilage is 0-5 cm. longer. Organ is 2 to 3 mm. at widest.

Relationship within the incisive canal: Jacobson’s organ lateral, blood-vessels medial.

Cow and calf.—Laterally Jacobson’s organ is a lengthy structure about 9 cm. long and 1 cm. wide, lying roughly horizontal and parallel with the palate.

The anterior portion of the organ passes within the incisive canal to the under surface of the bony palate in the same plane as the organ and then turns abruptly inwards and forwards within the thickness of the fibrous covering of the anterior portion of the palate where the incisive canal opens at the papilla palatina on either side.

FIG. 5.—Cow. Dissection showing body and orifice of Jacobson’s organ, anterior portion of palate cut away at an angle.

The anterior orifice of Jacobson’s organ opens as a narrow slit just before the incisive canal opens on the palate; it is therefore necessarÿ to dissect obliquely across the thickness of the palate to see the anterior portion of Jacobson’s organ.

Jacobson’s cartilage completely surrounds the organ and advances with it within the incisive canal as far as the opening of the organ. It is quite tightly apposed to the lower border of the cartilaginous nasal septum and appears to be closely attached thereto; careful dissection, however, shows that there is a thin layer of fibrous tissue intervening. Thus the relationship, as viewed from behind, is centrally the cartilaginous nasal septum, then a layer of fibrous tissue—thin at upper region and thicker below—-then Jacobson’s organ (oval in section) completely surrounded by Jacobson’s cartilage which is thicker

ow. Finally and laterally a thick layer of mucous membrane which is the mucous membrane of the septum and is continuous over the nasal floor—a prolongation sweeps as a tube into the incisive canal as previously described.

Contents of the incisive canal.—There is a small artery posteriorly, then nerve and a larger artery, and then Jacobson’s organ anteriorly, the arrangement within the canal from without in being—Jacobson's organ, nerve and artery.

Calf—The organ is nearly as long and as wide as in adult cow. It is interesting to see in calf that Jacobson’s cartilage is not adjacent to the side of nasal septal cartilage, but is suspended immediately below it by a fibrous ligament running the full length of the organ. Anteriorly, however, the cartilage becomes more firmly attached.

Cow, sheep and pig.—The incisive canal is very wide from front to back—narrow from side to side and runs at an angle of about 30 degrees from front to back, so that the premaxilla finishes, anteriorly to the canal, at an acute angle and the palate commences posteriorly also very sharply. The effect of the incisive canal is that of a sweep forwards and downwards of the mucous membrane into a narrow elongated tunnel opening by means of a very small orifice at the papilla palatina. 7 | Section of Odontology 47

Human Embryos Examined

Human specimens of the following crown rump lengths were examined in serial section.—12:5, 32, 35 (sagittal), 35, 37, 70, 80, 124 mm. (eight in all); seven in frontal section and one in sagittal section.

FIG. 6. FIG. 7. FIG. 6.—Human embryo (frontal section). 12°5 mm. c.r.l. Showing Jacobson’s organ just forming on left and lumen fully formed on right. Note absence of Jacobson’s cartilage. X 46.

FIG. Tr Haman embryo (sagittal section). 35 mm. c.r.l. Showing Jacobson’s organ in full. Anterior orifice to eft. x 46.

. 8.—Human embryo frontal section). 37 mm. c.r.l. Showing lumen of Jacobson’s organ. Note Jacobson’s cartilage just beginning. X 59.

+ 9.—Human embryo (frontal section) 70 mm. c.r.l. Beginning of Jacobson’s organ. Jacobson’s cartilages well shown. x 46.

Embryo 12-5 mm. c.r.l.—Jacobson’s organ lies in its usuai position and begins 600% from the tip of the embryo (nose). It consists of three definite portions: (a) a furrow in the mucous membrane 1004 long; (b) a tubular opening 204 long; (c) a body 100u long. Total length 220u.

In this specimen the “tail”, i.e. posterior tapering end, is very short. 48 Proceedings of the Royal Society of Medicine 8

There is no septal cartilage or Jacobson’s cartilage in this specimen. There is no trace of the tooth band, which confirms Meyer’s (Churchill) statement that this structure does not appear until 13 mm. stage.

Embryo 35 mm. c.r.l.—It is fortunately possible to study the embryology of the organ in embryos of this length—both frontally and sagittally.

Jacobson’s organ frontally—The first invagination of Jacobson’s organ begins as a furrow in the edge of nasal mucous membrane for three sections and then a fine tube within the mucous membrane for three sections, opening at 2.4.10 into the body.

Length of Jacobson’s organ in this specimen is furrow 304, tube 30u, body 350u, tail 140u. Total length 550.

Jacobson’s cartilage in its total length is 870x. It is 320u longer than Jacobson’s organ, appearing 50 before and ending 270y behind the “tail” of the organ.

Shape and description of Jacobson’s cartilage.—The structure varies very much in shape throughout its length; in general it forms a complete protection to the lower aspect of Jacobson’s organ. It is mainly free at its anterior end, but becomes closely apposed to the cartilage of the nasal septum posteriorly; at no time does Jacobson’s cartilage become merged into the nasal septum; there is always a layer of tissue between—only one cell in thickness in much of its length.

It first appears as an isolated ovoid piece of cartilage below and some distance away from the septal cartilage.

It approximates the tip of the septal cartilage as an upright oblong cartilage at 3.1.9, 210 later, and remains in close contact here, but varying in shape, oblong to triangular, “L” shaped, crescent shaped and ovoid again until section 4.1.12, ï.e. 510u in length, when it is again separate from the septal cartilage as a small ovoid cartilage and dis- appears at section 4.3.2; so that the relationship of Jacobson’s cartilage to the septal cartilage is: Anterior portion free of septal cartilage 210u; middle portion in contact with septal cartilage 510u; posterior portion free of septal cartilage 150w.

Relationship to incisor teeth—-The first incisor tooth first arises at 2.2.4 and ends at 2.3.10 where the tooth band immediately gives rise to the second incisor, i.e. 704 before the beginning of Jacobson’s organ and practically the same level as beginning of Jacobson’s cartilage.

Embryo 35 mm. Cut in sagittal section.—Crown rump length 35,000u; width of head 6,500u; width of nasal cavitv proper one side 550u. There is, in addition, a narrow prolongation of the nasal cavity outwards of 130x (? antrum or other sinus); total width of nasal septum 370u; width of Jacobson’s organ at its widest (one side) 80u; width of Jacobson’s organ at its widest (other side) 90. From this measurement it will be seen that the two Jacobson’s organs occupy approximately one-half of the width of the septum. Total length of organ is 550u.

Jacobson’s cartilage is a total width of 120u and lies underneath Jacobson’s organ over- lapping both sides of the organ about 104 or 20u. In shape longitudinally it varies from nearly round, through crescent shape to club shape, when in the middle of its width and at its posterior end it becomes closely apposed to the cartilaginous septum. Length of cartilage is 870y.

Relationship to the incisor teeth—The whole of the organ, including its orifice, is just behind the forming second incisor.

Embryo 37 mm. c.r.l. Frontally.—Jacobson's organ begins at 121 sections (1,210u) from tip of nose. Jacobson’s organ is present in 37 sections = length 3704 and Jacobson's cartilage is 570u.

This specimen is interesting because Jacobson’s cartilage begins 1004 behind the first invagination of Jacobson’s organ.

Size of organ invagination, furrow and tubular entrance 90u; body 250; tail 304.

In this specimen Jacobson’s organ begins and ends at the same levels on both sides. In the other specimens examined, Jacobson’s organ is not symmetrical, but begins and ends several u later on one side than the other.

Jacobson’s cartilage shows much the same course and variations in size as in the 35 mm. specimen described above; it is first attached to the septal cartilage at its commencement and becomes free at section 5.2.8, i.e. there is a posterior unattached portion of Jacobson’s cartilage of 70u, i.e. length of Jacobson’s cartilage = 570.

Relationship to incisor teeth.—The first invagination of Jacobson’s organ coincides with the first heaping up of epithelium of the tooth band in the formation of the first incisor tooth and its “tail” terminates just at the plane where the epithelium is heaping up to form the primordium of the second incisor, i.e. rather more forward than in the others described. °

Embryo 70 mm. c.r.l.—In this specimen both Jacobson’s organs begin at section 8.1.3; one ends at 9.4.3; i.e. length (a) 650u, (b) 750p. 9 Section of Odontology 49

Jacobson'’s cartilage begins at section 5.3.1 as small outgrowths laterally at the tip of the nasal septum (i.e. a small separate anterior portion of 80u) at 5.4.1 the outgrowths become isolated, slightly smaller, then nearly horizontal—split into smaller portions and after changes in shape similar to those dissected in the 35 mm. specimen; the cartilage becomes closely apposed to the septal cartilage at 8.1.1, i.e. just before first invagination of Jacobson’s organ and settles down to a long thin downward projection of cartilage curving slightly outward at its lower end. Unfortunately the specimen ends at section 10.6.6 and as the cartilage is still present there, no length can be given for it.

Relationship to incisor teeth.—The first incisor tooth germ ends and second begins at 7.4.1. The latter is well shaped at section 8.1.3 where Jacobson’s organ commences (this is about half-way through the tooth germ); at section 8.4.5 the shape of the second incisor is just ended and the tooth band is continuing towards the canine tooth.


Jacobson’s organ is found in its typical arrangement in all of eight human embryos examined; Jacobson’s cartilage is present as a protective covering in all except the smallest (12-5 mm.).

The organ is relatively large in the 12:5 mm. specimen and is of diminishing size, relatively, as the size of the embryo increases.

There is no constant relationship between length of embrvo—length of Jacobson's organ—length of Jacobson’s cartilage—position of Jacobson’s organ vis-à-vis Jacobson's cartilage, and to position of developing incisor teeth.

Sizes.—In 12-5 mm. specimen Jacobson's organ is 2204 long; 35 mm. specimen Jacobson's organ is 550u long; 37 mm. specimen Jacobson’s organ is 370x long; 70 mm. specimen Jacobson’s organ is (a) 650u long, (b) 750u long.

In 12:5 mm. specimen Jacobson's cartilage is not present; 35 mm. specimen Jacobson's cartilage is 870u long; 37 mm. specimen Jacobson’s cartilage is 570u long; 70 mm. specimen Jacobson’s cartilage is 19504 present on the slides + an unknown further length.


It is rather remarkable as à result of study of the literature to find that many anatomists and embryologists confuse the incisive canal with the tubular part of Jacobson’s organ, thus clouding the fact that there are two general patterns of Jacobson’s organ: (a) As in human—opening in anterior nares (i.e. remote from the incisive canal); (b) as in most mammals—opening within Stenson’s canal (i.e. within the incisive canal).

A similar misunderstanding occurs in regard to the association of Jacobson's organ with Jacobson’s cartilage; there äppear to have been three general views: (a) Jacobson's organ and Jacobson’s cartilage are the same structure; (b) Jacobson’s organ is associated with and protected by Jacobson’s cartilage; (c) that the two structures are quite unrelated.

In spite of these contrary views the general view among embryologists is that the close and intimate association with a protecting cartilage is evidence that the organ is Jacobson’s organ. Possession of Jacobson’s cartilage may be taken as confirming the presence or pre- vious existence of Jacobson’s organ, as the cartilage is developed merely as a protection to the organ.

In calf, dissection shows Jacobson’s cartilage to be in the same dependent position as is the case in human embryos.

As to the opening of the anterior orifice of the organ there can be no doubt that in some animals the organ opens anteriorly remote from the incisive canal; nevertheless, it is apparent that the typical animal has the duct opening within the incisive canal.

The statement bv Watson-Williams is confirmed. It is not usually possible to see Jacobson’s organ in human adults, and onlv by a careful dissection is an occasional one found.

It must be granted that Jacobson’s organ, even in humans, had some original importance -—Franke quotes Keibel finding the organ in an embryo of 8 mm. and Peter in one of 9-2 mm., and the present writer shows it extremely well developed in one of 12:5 mm.

In adult humans the length as described by various authors is from 2-28 to 8:43 mm.— a human specimen is described possessing Jacobson’s organ of 8 mm. length.

Franke describes the organ as being about 1 cm. above the floor of the nose, Külliker 8-5 mm. In the specimen described in this paper the distance was 1 cm.

The interior of the organ is highly specialized, with columnar cells on the innermost layer (i.e. lining the lumen of the organ) and a glandular type of epithelium on the medial aspect of its cavity.

The investigation of Broom into the morphology of hyrax shows how the possession 50 Proceedings of the Royal Society of Medicine 10

of a typical Jacobson’s organ and its position and structure can aid in the exact allocation of animals whose species is doubtful. Weber's statement that in mammals the anterior part of Jacobson’s cartilage usually remains in contact with the septum, and appears to rise from the anterior part of the septum and to extend free backwards is confirmed in the case of pig.

The statement by Neal and Rand that what is left of Jacobson’s organ in man enters into the formation of the incisive canal is not confirmed. Gegenbaur finds difficulty in accepting the fact that Jacobson’s organ is the same structure in man as in other animals, but dissection shows it to be in approximately the same position in human as in other mammals, and embryological study shows the human organ developing much the same as in the lower animals.

The writer acknowledges the kindness of Professor Smout and Dr. Brandt for advice and encouragement and for permission to use specimens; to Mr. Bond, F.R.CS., for help in dissections; to Mr. Allan, Veterinary Surgeon, for specimens; to Mr. Pardoe for photo- graphs and illustrations, and to all others who have helped by providing specimens, references and other assistance.

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