A Further Contribution to the Minute Anatomy of the Organ of Jacobson in the Guinea-Pig

In my last paper on this subject (this Journal, January, 1881), I have given a detailed description of the relations and minute structure of the Organ of Jacobson in the Guinea-pig. This description, although referring to the greater part of the Jacobson’s tubes, did not embrace the relations and structure of the anterior and posterior extremity of these organs. Extended observations have placed me in the position to give now a detailed account also of these parts in the adult guinea-pig.

Jacobson, Gratiolet, Balogh, Fleischer and others, describe the organ, of Jacobson of mammals as opening into the ductus Stenonianus, and in my first paper on this subject (this Journal, January, 1881) I had also accepted this view for the guinea-pig; but on more careful examination, with a view to definitely ascertain whether this be the case, I made the unexpected observation that the tubes (organs) of Jacobson do not open into the Stenonian ducts but stand in a free and open communication with the anterior part of the nasal cavity, or more correctly speaking, with the lower nasal furrow, that is, the furrow along the bottom of the nasal septum. As is well known the organs of Jacobson develop as diverticula of the front part of the primary nasal pits. Later on, in the mammal, they are placed in communication with the Stenonian canals, while their communication with the nasal cavity is lost. But in the adult guineapig there is no such relation, since the communication with the nasal cavity persists, and this opening of the tubes of Jacobson into the latter will be spoken of below as the mouth of the organ of Jacobson. That this persistence of an open communication of the Jacobson’s organs with the nasal cavity is of great importance I need hardly say, and I would only remind the reader that it is exactly the assumed non-existence of such a communication with the nasal cavity, which made it very difficult to ascribe to these organs in the mammal a satisfactory function in conformity with their rich supply with olfactory nerve branches and with the presence of their sensory epithelium. This communication being now found in the guinea-pig¹ there is of course no difficulty whatever in ascribing to the organ of Jacobson in this animal a function similar to that of the olfactory mucous membrane, but probably of a more specific nature, as I have already hinted at in my last communication. Whether in other mammals this communication with the nasal cavity persists, will be a subject to which I soon hope to devote myself.

Examining a series of vertical transverse sections through the front part of the nasal organ of the guinea-pig, the organ having been previously suitably prepared (see my paper in this Journal for January, 1881), we meet with appearances of the several parts, very accurately shown in the figures 1 to 6 of Plates XVI and XVII.

Fig. 1 is a transverse section through the most anterior part of the nasal organ. The relation of the cartilaginous septum to the lower turbinated bone, or lower concha nasalis, and further, of this to the alveolar process of the superior maxilla, are very well illustrated, the drawings being all made with the camera lucida, the relative proportions and sizes are all very accurately preserved. It will be seen in fig. 1 that the cartilaginous septum nasale forms an unbroken continuity with the cartilage representing here, i. e. in the front part of the nasal organ, the support of the lower concha. This continuity is brought about, on each side, by a curved, more or less trough-shaped cartilage plate extending on the inner surface of the alveolar process of the superior maxilla to the angular piece of cartilage that forms the support of the lower concha. But this continuation is more or less broken as we pass a little way backwards (see fig. 2). Here we find the above-named curved cartilage plate more or less separated from the lower margin of the septum as well as from the cartilage piece of the concha.

In my former communication I have used the term “concha “of the German anatomists for the “turbinated bone “of English text books. I consider the former term preferable, because it gives to the organ a name independent of its structure. In our case, i. e. in the front part of the nasal organ where there is no bone contained in it yet, it would be incorrect to speak of a turbinated ‘bone.’

In fig. 3, which is taken a little behind fig. 2, this separation is complete, and, in addition, we find also the cartilage of the concha reduced considerably in extent, being now for the greater part replaced by bone, with the exception of an oblong angular piece, which extends above the nasolachrymal duct (see below).

In the sections still further behind that of which fig. 3 is a representation the individuality of the above curved cartilage plate is well seen. Its shape and relation to the septum are now different from that before mentioned, as is easily understood from a reference to this fig. 3, and it is, therefore, unnecessary to enter into any lengthy description. This curved cartilage plate is the front end of the cartilage surrounding the Jacobson’s organ, i. e. the Jacobson’s cartilage, and as such is referred to in the figures at 3. While in the parts delineated in figs. 1, 2, and 3 the concave surface of Jacobson’s cartilage is directed upwards, forming, at the same time, the bottom of the lower nasal furrow (see the figures), in the parts further backwards, such as are shown in figs. 4 and 5, the cartilage becomes so changed that its concave surface is directed outwards, while its convex surface is in close contact with the lower margin of the cartilage of the septum, but separated from this latter by the respective perichondrium and a small amount of loose connective tissue with fat cells (see the figures).

As is also well shown in the drawings, the two extremities of Jacobson’s cartilage, especially the upper one, become very bulky as we pass farther backwards; (see fig. 6). Still more backwards the Jacobson’s cartilage assumes the shape of a more or less complete capsule around the organ of Jacobson on each side, such as 1 have described and figured in my previous memoir, and for this reason I need not further enter into this subject.

Towards the posterior extremity of Jacobson’s organ the cartilage so alters that the lower part gradually altogether ceases, and only the upper plough-shaped portion (see fig. 2 in my former memoir) remains; its channels, including the large afferent branches of the vessels and nerves of the organ of Jacobson become gradually enlarged, and finally all traces of the cartilage are lost. But this total disappearance of the cartilage of Jacobson occurs long before the hind or caecal extremity of the organ of Jacobson is reached, its place being taken by the bone of the nasal crista; see figs. 7.

Another point to be noticed in figs. 4, 6, and 7 of the present memoir is the relation of the upper maxilla, or, more correctly speaking, of the nasal crista, to the Jacobson’s cartilage. Beginning with a part illustrated in fig. 4 we see at 11 the first indication of the nasal crista of the upper maxilla, in the shape of a thin lamella of bone, extending along the convex surface of Jacobson’s cartilage. It soon becomes very conspicuous, covering not only the convex surface of the cartilage, but gradually embracing the greater part of the circumference of the organ of Jacobson, as shown in figs. 1 and 2 of my paper in the January number of this Journal. In the posterior portion of the organ of Jacobson, viz. where the cartilage of Jacobson is wanting, as has been just mentioned, the former, i. e. the organ of Jacobson, is entirely enclosed in the osseous substance of the nasal crista, as is shown in fig. 7 of the present memoir.

In figs. 1,2, and 3, i. e. in the anterior portion of the nasal organ, the lower nasal furrow (4) is lined with columnar ciliated epithelium, like that of the septum; it has been minutely described in my former memoir, and need not, therefore, be referred to here any further. The very bottom of the furrow, however, is lined with stratified pavement epithelium, of which the superficial layers consist of sqamous epithelial cells, each possessing a flattened nucleus. In the preparations from which the above figures are taken these superficial layers are more or less loosely attached to the rest of the epithelium, hence appear as if desquamating. The stratified epithelium, as a whole, is stained very much deeper in these preparations than the columnar epithelium, and is therefore very conspicuous in the drawings.

Such is the state of the epithelium at the bottom of the furrow in the front part (figs. 1, 2, and 3). But, going further back, we find that this part of the furrow, viz. the one lined with stratified pavement epithelium changes its position, inasmuch as it does not now occupy the very bottom of the furrow, but gradually extends, inwards and upwards towards the concave surface of the Jacobson’s cartilage. An inspection of figs. 4 and 5 will make this easily understood. At 12 in these figures the changed position of the part covered with stratified pavement epithelium is well seen.

Now, this pit, viz. marked 12, is the commencement of the organ or tube of Jacobson, or, more correctly speaking, the anterior opening of this latter into the nasal furrow; we shall call it the mouth of Jacobson’s organ. Its diameter is about 0·05 mm., not including the lining epithelium, whose thickness is about 0·057 mm.

A little way further back (see fig. 5) we meet already with the well-formed tube of Jacobson, and we still recognise here the stratified pavement epithelium, occupying, as must be expected from what has been said before, the upper part of the tube; the lower part is lined with columnar ciliated epithelium, like that of the nasal furrow. A little further back the epithelium lining the tube is uniform on all sides, being ciliated columnar epithelium, such as has been minutely described in my former paper as lining the lateral wall of the organ of Jacobson.

Still further back (see fig. 6) we meet with this important alteration in the epithelium, that the median wall is lined with the thick sensory epithelium minutely described in my first paper. The tube, as a whole, has not, however, got yet its characteristic shape, i. e. so compressed from side to side,that its lumen is kidney shaped in transverse section (see figs. 1 and 2 in my first paper); this shape is, however, soon obtained, and the organ retains.it to near its posterior extremity. Before this, however, is reached the direction of the lumen, and consequently of the walls, is more or less oblique and slanting downwards and inwards. In this oblique position we find chiefly the epithelium and the cavernous layer.

As regards the structure of the wall of the tube of Jacobson in its commencement, it is similar to that of the nasal furrow, viz. the subepithelial membrane is connective tissue infiltrated with numerous, lymph,-corpuscles, and resembling more or less diffuse adenoid tissue.

Already at the mouth of Jacobson’s tube (12 in figs. 4 and 5) we find large veins forming a plexus and representing the rudiment, of. the cavernous tissue described in my first paper. This plexus becomes more developed as we pass backwards, and from its first appearance, i. e. at the mouth of Jacobson’s organ, to the posterior extremity of this (see below), does not encroach on the median wall, i.e. the wall nearest the septum. In the parts from which fig. 6 is taken-, but not further in front, we find between the vessels of the cavernous tissue already bundles of non-striped muscular tissue.

Longitudinal sections through the organ of Jacobson prove that a considerable posterior portion is without any cartilage, and is enclosed altogether in the bone of the crista nasalis, as mentioned above.

The posterior cæcal extremity of the organ is slightly curved inwards and upwards; it is smaller in diameter than the rest of the organ; its lumen is circular in cross section. The median wall of this extremity is not lined with any sensory epithelium, this having previously suddenly come to an end; we find here everywhere only columnar epithelium, similar to that of the lateral wall of the preceding parts.

In my first paper I have shown that the layer of (serous) glands is situated outside the cavernous layer, and extends in the lateral wall from the lower sulcus to the upper sulcus, but its bulk lies about the lower sulcus, into which the ducts chiefly’ open (see figs. 1 and 2 of my former paper). As we pass backwards, but long before the extremity of the organ is reached, we find the area in which the glands extend considerably increased, for many glands are now found also about the upper sulcus, and their ducts open into this latter. In the part which we just before described as the posterior extremity, viz. the narrow hind part with the cylindrical lumen, and without any sensory epithelium on the median wall, we find the layer of glands forming a complete investment and occupying almost the whole periphery of the organ (see fig. 7).

Another difference between the posterior section of the organ and the rest lies in the change the cavernous tissue undergoes in that extremity. As is shown in fig. 7, its position is not the same that it was before (compare figs. I and 2 of my first memoir), viz. occupying the lateral wall only, for, owing to the altered position of the lumen—this latter being not vertically but obliquely placed—the cavernous tissue now occupies the lower wall. At the same time the number of vessels and the amount of non-striped muscle tissue are greatly increased, although the individual vessels are not of so large a size as in preceding portions of the organ.

The plexus of non-striped muscular tissue forming the matrix of the cavernous layer is best developed in the extremity itself, and, together with the plexus of veins of the cavernous layer and the gland layer outside, extends for some little distance behind the caecal end. In longitudinal sections comprising the posterior portion of the organ of Jacobson, these plexuses of bundles of non-striped muscular cells, and of veins between them, is very finely seen.

The tube which I described and figured in fig. I¹ in my first memoir was there named the “accessory organ of Jacobson.” But this is the naso-lachrymal duct; this was suggested to me through the kindness of Dr. Allen Thomson, by Prof. Kölliker, of Würzburg, and on careful dissection I have convinced myself that this is really the case.

It extends anteriorly and posteriorly considerably beyond the region of the organ of Jacobson. Anteriorly the nasolachrymal ducts are met with, in vertical transverse sections through the nasal organ, some distance in front of Jacobson’s organs, as minute tubes, in the same position and of the same nature as described in my first memoir, as will be easily understood on comparing the figures 1, 2, 3, and 4 accompanying the present paper. Also backwards for a very long distance beyond the region of the organ of Jacobson about 10·12 mm.; the naso-lachrymal ducts retain the same position, viz. between the nasal furrow and the alveolar process of the upper maxilla. As I mentioned in my first paper, this duct is slightly flattened from side to side, and the diameter enlarges considerably posteriorly; in the region of the hind extremity of the organ of Jacobson the diameters of the naso-lachrymal duct (5 in fig. 7) are these:

Behind the region of the organ of Jacobson the nasolachrymal ducts increase still more in diameter, the transverse diameter of the lumen alone amounting in the broadest part of the tube to 1·125 mm.; they become at the same time cylindrical, i.e. less flattened from side to side. As regards the structure of the naso-lachrymal duct I have little to add to my previous description as far as that part is concerned, that belongs to the region of the organ of Jacobson. In the whole extent of the duct I find in close proximity to the epithelium lining the interior of the duct, and described minutely in my first memoir, but separated from it (epithelium) by a thin fibrous layer, i. e. the subepithelial fibrous layer, a plexus of large veins, most of these running a longitudinal course. The wall of these veins is exceedingly thin and appears to consist almost entirely of the endothelial membrane lining the lumen. Had I not seen the blood capillaries in connection with them, and had I not found some of them containing blood, I might easily have mistaken them for lymphatics. This plexus, which I will call the “subepithelial venous plexus,” is well seen n the region of the posterior extremity of the organ of Jacobson (see figs. 9, 10); it reaches its greatest development in the region behind the organ of Jacobson. In fig. 7 it is also noticed that the rest of the wall of the naso-lachrymal duct is made up of a very loose fibrous connective tissue; the thickness of the wall is greatest in an upward and downward vertical direction. Scattered lymph-corpuscles and more or less well-defined accumulations of them, i.e. true lymph-follicles, are met with in the upper wall of the duct close to the epithelium (see figs. 7 and 8).

Henle¹ mentions in the lower portion of the human naso-lachrymal ducts the richness of its wall in lymphatic tissue and in a cavernous tissue, this latter being a continuation of the cavernous tissue of the lower nasal concha.

In fig. 8 I have given an accurate representation of the wall of the naso-lachrymal duct, and it will be here _;seen that the stratified columnar epithelium, with the vascular intraepithelial vesicles or cavities,. the subepithelial fibrous layer, and the subepithelial venous plex.us are well.marked.

I cannot ascertain whether the superficial cells bear cilia or not. In my last paper I have given several reasons why I think, that they are ciliated but 1 have not been able to get further in this matter. Henle³ maintains that in man the epithelium lining the duct is simple columnar ciliated epithelium as against R. Maier,³ who describes it as stratified columnar non-ciliated epithelium.

The thickness of the epithelium is here about 0·068, the thickness of the sub-epithelial fibrous layer is 0·012—0·016 mm., and the diameter of the veins of the sub-epithelial plexus is between 0·028 and 0·04 mm.

The rest of the wall of the duct, in fig. 8, shows an artery ascending towards the internal surface and connected at its capillary end with a lymph-follicle.

The lymph-follicle, which I described and figured in fig. 1 of my first memoir, is not in reality a solitary follicle but is one of a patch of lymph-follicles extending in a longitudinal direction, and therefore seen in the figure in transverse section. Besides these follicles I find one large patch of lymph-follicles on each side of, and close to the epithelium lining the lateral wall of the lower nasal furrow a little behind the region of the organ of Jacobson. The long diameter of this patch, i. e. anterio-posteriorly, is about 3’4 mm., the thickness diameter, i.e. from side to side is about 0·45 mm. The individual follicles of the patch are spherical, closely placed side by side, and in some places their outlines are indistinct; the diameter of the largest folliclesis about 0·3—0·45 mm.

Both the upper and lower wall of the duct contains a great many wavy and more or less convoluted arterial vessels connected with one another; in fig. 7 they are seen cut in various directions. The capillaries proceeding from these arteries are contained in the subepithelial fibrous layer above mentioned, and some of the capillaries enter the intraepithelial spaces described in my first memoir. The capillaries lead into the subepithelial venous plexus, and small veins come out from this plexus and pass into the outer portion of the wall of the naso-lachrymal duct.

In the embryo guinea-pig that I have examined hitherto, at a time when the organ of Jacobson is well developed, also the naso-lachrymal ducts are distinctly visible, bearing the same position and relation to the surrounding parts as in the adult animal. ‘

An embryo guinea-pig, whose total length from vertex of the head to the tail was 4 centimètres, while the long diameter of the head, i. e. from the tip of the nose to the occiput was 2 centimètres, has been the material from which I have made vertical transverse sections through the nasal organ. In a section through the anterior parts, containing the Jacobson’s organ as closed tubes, it is noticed that the cartilage of Jacobson forms almost a complete capsule round the organ of Jacobson, the lateral and median wall of the latter being easily distinguishable. Sections made of parts a little further back show, the cartilage capsule of Jacobson open on the upper part, so as to allow the entrance of the nervous and vascular branches; the inner or median lamella of the capsule is at the same time much higher than the outer one, and in this state the shape of the cartilage resembles very much that of the adult rabbit, as I shall have soon an opportunity of showing.

The relations of Jacobson’s cartilage to the nasal septum in the front part of the nasal organ and the opening of the anterior extremity of the organ of Jacobson into the nasal furrow, are exactly the same in this embryo as described above of the adult animal. There is, however, this interesting condition of the lower nasal furrow throughout the front part of the nasal organ, viz. that the furrow itself is not formed yet, but the stratified epithelium lining the median and lateral wall of the septum is fused into one solid membrane. But there are smaller or larger cavities visible in this membrane; by confluence of these along a definite middle plane the furrow becomes gradually established.

The shape and relation of the naso-lachrymal ducts to the cartilage of the concha and to the upper maxilla is the same as in the adult animal. The epithelium lining itis stratified epithelium composed of a deep layer of columnar cells, and inside these are a good many layers of polyhedral cells.

In the front part the lumen of the duct is not at all distinct; in the posterior portion of the duct the lumen becomes very conspicuous, and the epithelium resembles, in all respects, stratified pavement epithelium, the superficial cells being, however, not much flattened.

I measured the thickness of the epithelium lining the naso-lachrymal duct in this embryo, and I find it to be about 0·068 mm., the lumen of the duct being 0 22—0’03 mm. In a part behind the region of the organ of Jacobson the thickness of the epithelium is smaller, being 0·056, while the lumen is 012 mm. ‘

For the sake of completeness I append here a few points concerning the structure of the Stenonian ducts, which, as is well known, pass closely side by side, and in the median line, from the nasal to the oral cavity.

In the adult guinea-pig the nasal extremity of each of these ducts is an oblong cleft lined with a continuation of the mucous membrane of the lower nasal furrow; the epithelium is ciliated columnar epithelium, and underneath this is a membrane very vascular and infiltrated with lymphcorpuscles. There are no secreting glands, mucous or other, visible in this part, and the mucous membrane is in immediate contact with the bone of the palate.

As the ducts approach the oral cavity, but while still in the bone of the palate, they become much smaller, but in a transverse section are still cleft-like, and lined with stratified pavement epithelium, whose superficial cells are polyhedral. Having passed the bone and approaching the oral cavity, the ducts become still smaller, they remain cleftlike, and are lined with stratified pavement epithelium, whose superficial cells are as much flattened as those of the palatine mucous membrane. The mucosa underneath the epithelium of the ducts is dense fibrous tissue, and there are indications of minute papillæ. There is now already to be seen a trace of the Stenonian cartilage in the periphery of the wall of the ducts.

Still nearer towards the oral cavity, while the ducts enlarge in diameter, and while their shape becomes more cylindrical, the above rudiment of the cartilage forms now for each duct a curved plate, semicircular in transverse section, whose concave surface embraces the outer part of the wall of the duct.

The two ducts being close side by side, it follows that the two semilunar cartilages meet at their extremities, and thus form nearly a complete capsule for the two ducts (see figures 9 and 10). There is a smaller or larger apparently isolated nodule of cartilage found between the two ducts.

Just before the ducts open into the oral cavity the lumen becomes a little smaller, cylindrical, and there are here well-developed papillae, such as those of the palatine mucous membrane. The Stenonian cartilages have become confluent with their extremities, and present themselves now in transverse section as a beautiful heart-shaped capsule, in each of whose cavities lies one of the ducts, the apex of the heart being directed forwards, the notch backwards (see fig. 10). In connection with the apex one or more small pieces of cartilage are seen extending into the tissue separating the two ducts.

As regards its structure, the Stenonian cartilage differs widely from that of the cartilage of the nasal septum and of Jacobson’s cartilage, the Stenonian cartilage being elastic cartilage, i. e. dense networks of elastic fibrils, forming a sort of capsule around the individual cartilage cells. These latter are remarkable for being identical in appearance with well-formed fat-cells. Of the cartilage of the septum I have mentioned, in my first paper, that in many places the cartilage-cells are filled with numbers of minute fat globules, an appearance well known of some other hyaline cartilages; but here, i. e. in the Stenonian cartilages, we find each cartilage cell filled with one large oil globule. Being elastic or reticular cartilage there is then, a great similarity between the Stenonian cartilage of the guinea-pig and the cartilage of the epiglottis of some animals (rabbit, cat, dog), where the cells are likewise transformed into fat-cells.

According to Balogh¹, the Stenonian cartilage in the sheep is hyaline, and the epithelium lining the duct, speaking of the Stenonian duct only as situated in the mucous membrane of the palatum durum, is stratified and composed of flattened and more or less hexagonal cells.

Kolliker³ found, in the adult human subject, the duct lined with ciliated columnar epithelium. Both Balogh, for the Stenonian duct of the sheep, and Kolliker, for that of man, mention mucous glands embedded in the wall of the duct and opening into its lumen.

In the guinea-pig I have searched in vain for these glands; except an occasional fold-like unevenness, I cannot find anything of glands.

The measurements which I made of transverse sections through the Stenonian ducts iu the guinea-pig are these:

In all these measurements it must be understood that the transverse diameters, i.e. the anterio-posterior as well as that from side to side, comprise the lumen and the lining epithelium only, the fibrous coat forming the proper wall of the ducts not being included.