Talk:Paper - The organ of jacobson in the horse, ox, camel and pig (1925)

From Embryology


By Carr. F. C. MINETT, M.B.E., B.Sc. Royal Army Veterinary Corps


‘Tue organ of Jacobson has been carefully examined and described in a number of animals. It has been found to exist in all the mammals which have been examined (Symington (1891), von Brunn (1892), Klein (1881), Read (1908) and others), but it is not confined to this class as among reptiles the structure is present in a well-developed state in many lizards and snakes and among certain of the higher amphibians also. It reaches its highest development however in certain Monotremes such as Ornithorhynchus, Echidna, Monitor (Broom, 1895). In man it is rudimentary while in Carnivores and Herbivores it is well developed. The importance of the organ from the point of view of zoological classification has been suggested by Broom (1897). A short summary of existing knowledge on the subject will be found in a small text-book by Parker (1922).

Strange as it may appear, in the literature on the subject there is a curious lack of reference to the organ in the horse, and no very close description of it has appeared, though the structure has no doubt been examined many times. The older text-books of veterinary anatomy give hopelessly inaccurate accounts while in some of the newer works, which are of course primarily intended for students and practitioners, the accounts are usually confined to four or five lines. ,

I have not found any description of the structure in the camel.

Acting on a suggestion by Major-General Sir F. Smith, K.C.M.G., it was resolved to attempt a closer examination of the structure in certain mammals which were available.


The organs are to be found on the floor of the nasal cavity beneath the mucous lining and on each side of the base of the septum. They are tubular _ in form, ending blindly posteriorly while anteriorly they join the nasopalatine canals and in this way communicate with both the nose and the mouth. In its highest development the organ extends anteriorly beyond this canal for some distance to end blindly or it may even extend into the lateral cartilages of the nose as in some lizards (Broom, 1895). The tube is a mucous one with a sensory epithelial lining, olfactory in function, and is invested partially or The Organ of Jacobson in the Horse, Ox, Camel and Pig 111

completely by a sheath of hyaline cartilage. In section the lumen of this tube is usually found to be kidney-shaped or half-moon shaped.


The organ is comparatively well developed in the horse, being 12-13 cm. long in an animal of medium size, the posterior blind extremity being thus about level with the second premolar tooth. Its cartilaginous sheath lies in a groove formed at the junction of the vomer with the symphysis of the palatine processes of the superior maxillary bones and is closely applied to the bony tissue, especially anteriorly where the grooves deepen.

If sections be made of the organs at different levels it is seen that the lumen varies in size and shape. Thus at any point along the posterior seven-eighths the lumen is revealed as a crescentic slit about 3mm. in extent, the concavity being to the outer side. Anteriorly the lumen becomes circular and constricted


Fig. 1. Fig. 2.

to a diameter of 1 mm. where it communicates with the nasopalatine canal by an elliptical opening on its inner wall, the opening being about 1 cm. from the nasal extremity of the canal.

The nasopalatine or Stenson’s canal is about 3 cm. in length, the posterior opening being at the extreme anterior corner of the floor of the nasal fossa about 5 cm. behind the lachrymal opening, whence it is directed downwards - and forwards to end blindly in the cartilage filling the incisor cleft. The failure of this canal to form a complete channel between the nose and the palate in the horse is to be particularly noted as this is exceptional. A distance of about 1 cm. separates the blind end of the canal from the surface of the hard palate.

In the published accounts of Jacobson’s organ, a good deal of stress has been laid on the arrangement of the investing cartilage, this being essentially different in the Prototheria and in the Eutheria. In the horse for the greater 112 F.C. Minett

part of its extent the cartilaginous covering conforms to what is the usual type in Eutheria as may be seen in fig. 1, in which the relation to the vomer and the shape and position of the organ may also be noted. Posterior to this the tube in places is extremely thin or entirely absent at its floor, the outer wall being quite independent of the inner at that point. For a short distance anteriorly the cartilaginous covering becomes a complete tube (fig. 2) and here it joins a cartilaginous lamella placed on the inner wall of the superior maxilla.

Fig. 3 shows Stenson’s canal in section close to its blind extremity. Fig. 4 represents the face of a section taken about 1 cm. anterior to fig. 8; therefore, by comparing the two it will be seen that the cartilage covering Jacobson’s organ is continuous anteriorly with the expanded base of the septum nasi where this rests upon the palatine processes of the premaxillary bones and

Fig. 3 Fig. 4

with the cartilage of the incisor cleft. Posteriorly the tube first becomes incomplete as to its outer wall, the inner wall persisting for some 4 or 5 em. further back where it maintains its position in the shallow depression on the outer surface of the vomer.

No essential differences are to be observed in the structure in the ass and mule.


This is from two sources, olfactory and sphenopalatine, the innervation thus being similar in part to that of the nasal mucous membrane as a whole. Read (1908) describes in the dog the anterior ethmoidal nerve as supplying the organ also. This nerve no doubt corresponds with the nasal branch of the ophthalmic (M‘Fadyean). I have not been able to trace the fibres of the latter nerve as far as the organ in any of the animals here examined.

Olfactory. These can mostly be seen without dissection on the deep face of the septal mucous membrane (beneath a thin fibrous sheet) on carefully stripping this from the cartilage, where they appear as thin ‘greyish bands descending downwards and forwards from the region of the lateral masses. Many of these are extremely fine and are lost in the mucous membrane. The fibres however which reach Jacobson’s organ are mostly derived from one rather broad band which takes its origin from the posterior surface of the The Organ of Jacobson in the Horse, Ox, Camel and Pig 113

olfactory lobe. This branch passes inwards to enter a bony canal in the crista galli process, on emerging from which it lies for 2 or 8 cm. in a groove on the surface of the mesial ethmoidal plate. It enters the organ 2 or 3 cm. from its upper extremity and its fibres can be traced nearly as far as its nasal opening.

Sphenopalatine. This nerve issues from the sphenopalatine foramen in company with the artery and vein of the same name, and immediately divides into an outer and inner branch. The latter passes to the deep surface of the septal membrane where 3-5 cm. from its origin it divides into a number of small trunks which gradually diverge. Of the more superior of these one or more penetrate the organ, the others being distributed to the septal mem- brane. A larger inferior branch enters a bony canal in the side of the symphysis of the hard palate (where it accompanies branches of the palatolabial artery) whence it is eventually distributed to the palatal membrane behind the incisor teeth.

Bioop Surry

No vessels of any considerable size are to be found entering the organ. No doubt blood is received from at least two of the sources which supply the nasal cavity, viz., sphenopalatine and palatolabial.

Text-books of veterinary anatomy do not refer to the latter vessel supplying blood to the nasal cavity. It does so however through a branch which is usually given off from the left, though sometimes from the right, palatolabial artery about 4 cm. below the first premolar tooth. This branch passes obliquely upward to enter a bony canal in the symphysis of the palatine plates of the superior maxillae at their junction with the vomer, where it subsequently divides into two. Twigs from these two branches are to be found embracing the cartilage of the organ at intervals of its length—usually on its outer aspect—where they are distributed in the septal mucous membrane. It seems that ‘‘nasopalatolabial” would be a better designation for this artery in the horse.

Accompanying the organ are constantly to be found one or two veins which increase in calibre as they pass backwards to join the sphenopalatine vein.


The organ measures 15-16 cm. in length in the adult, and so is relatively longer than that in the horse which it resembles in general arrangement.

The tube is narrowest in its anterior third where its lining is black pig- mented; posteriorly it is more dilated and in section presents the usual reniform appearance (fig. 5). Anteriorly it opens into the nasal cavity above but in close proximity to the nasal opening of Stenson’s canal. It does not- open clearly into the canal of Stenson as in the horse. The nasal orifice of Sténson’s canal is oval and about 6 mm. in its long vertical diameter (fig. 6) The canal is continued downwards and forwards through the incisor cleft for 2-8 cm. where it ends blindly about 1 cm. from the surface of the hard palate.

Anatomy Lx 8 114 F.C. Minett

The investing cartilage is roughly similar to that in the horse but differs from it in being complete inferiorly and incomplete superiorly throughout its whole extent. Posteriorly its inner portion extends 1-2 cm. further back than

the outer and the blind extremity of the organ. Anteriorly the outer portion of the tube is again lost before the inner and from fig. 6 it may be seen that the wall of Stenson’s canal is supported outwardly by a cartilaginous lamella lining the inner wall of the premaxillary bone. At about this point too the persisting inner wall is connected to the base of the septum nasi.


Two bands of grey olfactory fibres can be seen passing forwards on the deep surface of the septal membrane from the region of the lateral masses, the lower of these being the larger. Both bands pass through the cleft at the upper border of the cartilage sheath and can be traced to the anterior third of the organ which they supply.

The sphenopalatine nerve can be distinguished as being whiter than the olfactory bands. It has much the same disposition as in the horse. A larger portion of the inner branch descends below the cartilage of the organ to supply the palatal membrane, the remainder supplies the nasal mucous membrane, and one small branch enters the organ.

Boop Supriy From the sphenopalatine artery. An important branch of this artery accompanies the inner branch of the nerve of the same name to be finally distributed to the palatal membrane. Branches from this vessel, which include one to the organ, supply a large part of the septal membrane where some appear to anastomose with descending branches of the nasal branch of the ophthalmic artery. No large vein accompanies the organ as in the horse.


Specimens were examined from adult cattle of the native Egyptian and Cyprus breeds, in both of which the structures were very similar. The organ The Organ of Jacobson in the Horse, Ox, Camel and Pig 115

is comparatively short and broad, the length being only 8 or 9cm. The lumen in transverse section appears as a crescentic slit as much as 7 mm. in extent, the concavity being outwards. Posteriorly the tube maintains this shape as far as the blind end but in the anterior third it becomes considerably con- stricted (about 8mm.). In the Egyptian ox it opens into the nasopalatine canal about 1 cm. from the nasal opening as in the horse, but in the Cyprus ox this opening is slit-like and only about 1 cm. from the palate. In one ox the length of the organ from the blind end to the anterior opening was nearly



Fig. 7

12 cm. the organ running in company with the nasopalatine canal for 3-5 cm. before opening into it. The nasopalatine canal in these species forms a complete tube (5 or 6 cm. long) between the nose and the mouth, the nasal opening, which is widely dilated, being situated in the extreme anterior corner of the floor of the cavity. The buccal opening, which is very constricted, is located at the bottom of a groove which encloses a heart-shaped area on the dental pad at the position shown in fig. 7.

The arrangement of the investing cartilage is as follows. At its centre it forms a complete tube, posteriorly it becomes more and more incomplete along its upper aspect to gradually disappear at a point 4 or 5 cm. above the blind end. Towards the anterior extremity the cartilage becomes incomplete on its outer side.

The nerve supply is similar to that in the horse.


The specimen examined was that of a very young pig, the head measuring 14 cm. long, while the organ was 2-3 cm. long, extending as far back as the level of the first premolar tooth.

The general arrangement of the organ and its cartilage may be seen in fig. 9. The lumen in section about its middle is slit-like, the slit being concave on its outer side. The cartilage is incomplete throughout; anteriorly it blends with that of the septum nasi; posteriorly its inner wall persists alone for a few millimetres beyond the blind end of the organ. The opening into the nagopalatine canal is relatively close to the palate, and the common ducts open on the palate in the positions shown in fig. 8. A fine bristle may be passed into each of these openings.

Two fine olfactory nerves may be seen coursing on the deep face of the 116 F.C. Minett

septal membrane to enter the organ which is also supplied with a small branch from the sphenopalatine. 4. HISTOLOGICAL In a transverse section as seen under the low power (displayed diagram- matically in fig. 10), the position of the parts is as follows. The lumen of the organ is slit-like with the outer portion of the lining pushed into a concavity of the inner, this lying in close proximity to the cartilage sheath. The olfactory


Fig. 9

nerve bundles are situated beneath the inner lining towards the upper aspect, while the sphenopalatine nerves and vessels are embedded in the connective tissue to the outer side of the tube. Numerous glands of the racemose type are also present in this connective tissue and are largely congregated around the extremities of the slit.

In sections from almost any part of the organ (except perhaps the anterior fifth) it is possible to distinguish the outer portion of the lining from the inner, that being respiratory and this olfactory in type. In the horse the inner lining, which is rather thicker than the outer, is formed of a layer of columnar The Organ of Jacobson in the Horse, Ox, Camel and Pig 117

cells the protoplasm of which in haematein and eosin preparations stains rather faintly in comparison with that of the outer. Between these may be seen a good many goblet cells and small lymphocytoid cells set on a deeper stratified layer. The surface of this portion always shows a quantity of adherent mucus.

In the outer lining the superficial cells are ciliated and set upon a layer of stratified cells with somewhat elongated nuclei. The distinction between the two classes of epithelium may be seen very clearly in eosin-Léffler methy- lene blue preparations in which the proper degree of differentiation with weak acid-alcohol has been attained. In the outer portion the nuclei of the basal cells stain rather diffusely and of a deep purple tint and are in sharp contrast to the nuclei of the ciliated cells, the nucleoli of which alone retain a distinct blue tint. In the inner lining the purple-staining basal cells are not present, the nuclei of the whole layer staining blue and not diffusely.

At the junctions between the two portions the lining is gradually thinned, the epithelium becoming cubical and finally almost flattened. It is in this situation that most of the ducts of the racemose glands open.

The lining of the nasopalatine canal is formed of two or three layers of flattened, pavement-like cells with oval nuclei and in the supporting connective tissue racemose glands are abundantly present.

In the other animals examined the histological features were essentially similar. In all the olfactory function appeared to be confined to the inner portion of the lining. In the bovine the organ becomes considerably constricted anteriorly where the whole lining seemed to be olfactory in type. The naso- palatine canal in this species is lined by stratified, squamous epithelium resembling that of the mouth. This epithelium is papillated, the papillae containing a network of capillaries, and in the connective tissue wall are numerous glands with ducts opening on the surface.


As nothing very precise is known regarding the physiology of the organ, a few words on the subject will not be out of place.

Firstly, there can be no doubt but that the function of the organ is olfactory. . The difficulty about the matter however is to understand how this function is exercised when one bears in mind that the anterior part of the tube is constricted and that the orifice is usually placed in a comparatively inaccessible position in the nasal cavity. Again it may be asked, what is the necessity for the provision of such a specialised organ of smell?

It was suggested (1) to measure the pressure required to bring about inflation of the tube, (2) to search for the mechanism which during life might lead to such inflation and so bring air into contact with the olfactory cells.

By introducing a small cannula into the nasal opening of Stenson’s canal in a fresh specimen (horse) and exerting gentle air pressure it was found to be quite an easy matter to inflate the organ, a pressure of about 40 mm. mercury 118 F. C. Minett

sufficing. The degree of inflation could be appreciated by noting the rise and fall of the nasal mucosa covering the cartilage sheath when the air pressure was varied. It should be noted that the end of the cannula was inserted into the nasal orifice of Stenson’s canal and not actually into the orifice of the organ of Jacobson. A careful search in the organ in the horse was made for striped or unstriped muscular tissue which presumably might cause dilatation of the tube during life. Attention was especially directed to the anterior portion of the organ since it is here that one might expect any dilating mech- anism to be best developed. While it can certainly be said that no striped muscle was encountered, one cannot be quite so dogmatic as to the presence or absence of unstriped muscle. However, except in one instance and apart from vessels there was no obvious stratification of these muscle cells, though no doubt they exist in the abundant connective tissue on the outer aspect of the organ. While therefore the organ may be easily inflated from the nasal cavity by artificial means, the exact manner in which air is brought into contact with its lining cells during life remains uncertain.

My sincere acknowledgments are due to Dr W. H. Wilson, Professor of Physiology in the School of Medicine, Cairo, for helpful advice respecting the concluding section of the work. It is unfortunate that for certain reasons I was unable to carry out all his suggested experiments.


Broom. Journ. Anat. vol. xxx, p. 70. 1895.

Journ. Anat. vol. Xxxt, p. 711. 1897.

Brunn, V. Archiv f. Mikr. Anat. Bd. xxx1x. 1892.

Kiem. Quart. Jour. Micr. Sc. vol. xx1. 1881.

—— Quart. Journ. Micr. Sc. vol. xxtt. 1882.

M‘FapyEan. Anatomy of the Horse. W. & A. K. Johnston.

PaRrkER. Monographs on Experimental Biology. Smell, Taste and Allied Senses in the Vertebrates. Lippincott, 1922.

Reap. Amer, Journ, Anat, vol. vim, p. 37. 1908.

Symineton. Journ. Anat. vol. xxvi, p. 371. 1891.


O=Organ of Jacobson. CP =Cartilaginous prolongation of septum nasi CS =Cartilaginous sheath. HP=Hard palate. ST.C =Stenson’s canal. DP=Dental pad. SN =Septum nasi. O.ST.C = Opening of Stenson’s canal. NMM =Nasal mucous membrane. GT =Gland tissue. V =Vein. MN =Medullated nerves. VOM =Vomer. ON = Olfactory nerves. CL =Cartilaginous lamella. ILO =Inner lining of organ. SM =Superior maxilla OLO = Outer lining of organ.

PM =Premaxilla.