Why do some people don't have a jaw
Both humans and animals have an intermediate bone in the upper jaw
A few attempts at osteological drawings have been pinned together here with the intention of presenting to connoisseurs and friends of comparative dissection a little discovery which I believe I have made.
In animal skulls it is easy to see that the upper jaw consists of more than one pair of bones.
Its front part is connected to the rear part by very visible seams and harmonies and makes up a pair of special bones. 
This anterior division of the upper jaw has been given the name intermaxillary bone. The ancients already knew this bone1 and recently it has become particularly remarkable, since it is given as a distinguishing mark between apes and humans. It has been ascribed to that sex, denied to it2, and if natural things did not show evidence, I would be shy to come forward and say that this bone department is also found in the human being.
I want to be as brief as possible, because by simply looking at and comparing several skulls, an already very simple assertion can be quickly assessed.
The bone I am talking about got its name from the fact that it slips between the two main bones of the upper jaw. It is itself composed of two pieces that meet in the middle of the face.
It is of very different shape in different animals and changes its formation very noticeably depending on whether it stretches forwards or withdraws. Its foremost, broadest and strongest part, to which I have given the name of the body, is arranged according to the type of food that nature has determined for the animal, for it must first touch, grasp, tear off, gnaw, cut up its food with this part appropriating them in one way or another; for this reason it is now flat and provided with cartilage, now armed with blunt or sharper incisors, or takes on a different shape suitable for food.
Through an appendage on the side it connects upwards with the upper jaw, the nasal bone and sometimes with the frontal bone. 
Inward of the first incisor, or from whatever place it was supposed to occupy, a spine or spine goes backward, rests on the palatal process of the upper jaw, and forms a groove itself in which the lower and anterior portions of the vomer or ploughshare pushes in. The canals (canales incisivi or naso-palatini) through which small blood vessels and nerve branches of the second branch of the fifth pair pass are formed through this spina, the lateral part of the body of this intermediate bone and the front part of the palatal process of the upper jaw.
These three parts are clearly shown with one glance at a horse skull on the first panel.
B. Apophysis maxillaris.
C. Apophysis palatina.
In these main parts, there are again many subdivisions to be noted and described. A Latin terminology, which I prepared with the help of Hofrat Loders and which I enclose here, will serve as a guide. It had so many difficulties if it was to fit all animals. Since in some parts certain parts recede very much, flow together and in others even disappear: this table will certainly allow some improvement if one wanted to go into more detail.
a. Superficies anterior.
1. Margo superior in quo nasal spine.
2. Margo inferior seu alveolaris.
3. Angulus inferior exterior corporis.
b. Superficies posterior, qua Os intermaxillare iungitur Apophysi palatinae Ossis maxillaris superioris.
c. Superficies lateralis exterior, qua Os intermaxillare iungitur Ossi maxillari superiori.
d. Superficies lateralis interior, qua alterum Os intermaxillare iungitur alteri. 
e. Superficies superior.
Margo anterior, in quo spina nasalis. vid. 1.
4. Margo posterior sive ora superior canalis naso-palatini.
5. Pars alveolaris.
6. Pars palatina.
7. Ora inferior canalis naso-palatini.
B. Apophysis maxillaris.
G. Superficies anterior.
H. Superficies lateralis interna.
8. Eminentia linearis.
i. Superficies lateralis externa.
k. Margo exterior.
l. Margo interior.
m. Margo posterior.
n. Angulus apophyseos maxillaris.
C. Apophysis palatina.
o. Extremitas anterior.
p. Extremitas posterior.
q. Superficies superior.
r. Superficies inferior.
see Superficies lateralis interna.
t. Superficies lateralis externa.
The letters and numbers by which the parts are identified on the protruding table are attached to both outlines and to some figures as well. Perhaps it will not be immediately apparent here and there why one has established this and that classification and chosen one or the other term. Nothing has happened without a cause, and if one looks through several skulls and compares them, the difficulty of what I have already thought of above will be even more apparent.
I now go to a brief display of the panels. The consistency and clarity of the figures will surpass me from a lengthy description, which in any case would only be unnecessary and annoying to persons who are familiar with such objects. Most of all, I wish my readers would have a chance to pick up the skulls themselves as they do so.
The second panel presents the front part of the ox's upper jaw from above, rather in natural size, the flat and broad body of which does not contain any incisors.
The third panel shows the intermaxillary bone of the horse, namely n. 1st by a third, n. 2nd and 3rd by half.
Tab. IV. Is the superficies lateralis interior ossis intermaxillaris of a horse on which the front incisor had fallen out and the following tooth is still in the hollow body of the ossis intermaxillaris.
Tab. V. is a fox skull on three sides. The canales naso-palatini are elongated here and better closed than in oxen and horses.
Tab. VI. The lion's intermaxillary bone from above and below. Note especially in n. 1. the suture which separates apophysin palatinam maxillae superioris from the ossi intermaxillari.
Tab. VII. Superficies lateralis interior of the intermaxillary bone of a young Trichechus rosmarus, laid out in red for greater clarity, at the same time as most of the superior maxillae.
Table VIII. Shows a monkey skull from the front and from below. One can see in n.2 how the suture emerges from the canalibus incisivis, runs towards the canine tooth, creeps forward along its alveolus and passes between the next incisor and the canine tooth, very close to this latter, and separates the two alveoli.
Tab. IX. and X. are these parts of a human skull.
The most visible part of the human eye is the intermaxillary bone in n. 1.. One can clearly see the suture that separates the intermaxillary bone from the apophysi palatina maxillae superioris. It emerges from the canalibus incisivis, the lower opening of which converges into a common hole that leads to the name of the foraminis incisivi or palatini anterioris or gustativi, and is lost between the canine and second incisors.
In n.2 it is a little harder to notice how the same suture shows itself in the base of the nose. This drawing is not the happiest; but on most  skulls, especially younger ones, one can see it very clearly.
Vesallus had already noticed that first suture3 and clearly indicated it in his figures. He says it reaches to the front of the dog's teeth, but nowhere does it penetrate so deeply that it can be assumed that it divides the upper jaw bone in two. In order to explain Galen, who had made his description only after an animal, he refers to the first figure on page 46, where he has added a dog's skull to the human skull in order to counteract the lapel of the medal, which is as it were more clearly pronounced on the animal To put readers in mind. He did not notice the second suture, which appears in the base of the nose, emerges from the canalibus naso-palatinis and can be followed as far as the area of the conchae inferioris. On the other hand, both can be found in the great osteology of albine on panel I with the letter M. He calls them Suturas maxillae superiori proprias.
They are not to be found in Cheselden's Osteographia, and there is no trace of them in John Hunter's Natural history of the human teeth; and yet they are more or less visible on every skull and, if one observes carefully, cannot be mistaken at all.
Tab. X. is half the upper jaw of a blown human skull, namely its inner side, through which both halves are connected to one another. The bone for which it was drawn was missing two front teeth, the canine and first molar. I did not want to have them supplemented, especially since what was missing was of no importance here; rather, one can see the intermaxillary bone quite freely. On the Pictura lineari I have washed what is undisputedly the intermaxillary bone with red. One can follow the suture from the alveoli of the incisor and dog's teeth to through the canals.
Beyond the spinae or Apophysis palatinae, which makes a kind of ridge here, it comes out again and is visible up to the eminentiam linear, where the concha inferior is located.
I drew a red asterisk in the pictura lineari.
Hold this table against Tab. VII. And you will find it admirable how the shape of the ossis intermaxillaris of such a monster as the Trichechus rosmarus must teach us to recognize and explain the same bone in humans. Also Tab. VI. n. 1., against Table IX. held n. 1. shows the same suture in the lion as in the human being most clearly. I am not saying anything about the monkey because the agreement is too conspicuous with this one.
So there will probably be no doubt that this bone division is found in both humans and animals, even though we can only determine exactly part of the boundaries of this bone in our sex, since the rest are fused and connected with the upper jaw in the most exact way . Thus there is not the slightest suture or harmony in the outer parts of the facial bones, which might lead one to the conjecture that this bone is separate in man.
It seems to me that the cause lies mainly in this.
This bone, which is so extraordinarily advanced in animals, retreats to a very small extent in humans. Take the skull of a child, or embryos, in front of you, and you will see how the germinating teeth cause such an urge on these parts and how tense the cuticles so that nature has to use all its forces to weave these parts together most intimately . Hold an animal skull against it, where the incisors have advanced so far and the urge against one another and against the dog's tooth is not so strong. It is the same inside the nasal cavity. As already noted above, the suture of the ossis intermaxillaris can be traced from the canalibus incisivis to the point where the ossa turbinata or conchae inferiores are attached. Here, then, the growth instinct of three  different bones acts against one another and connects them more precisely.
I am convinced that those who dig deeper into this science will find this point even more explainable. I have noticed various cases in which this bone is partly or completely fused in animals, and it will perhaps be possible to say more about it in the following. There are also several cases in which bones which can easily be separated in adult animals can no longer be separated even in children.
The tables that I enclose are mostly just the first attempt at work by a young artist who has improved with the work. Only the third and seventh panels are actually worked entirely according to the Camperian method; but afterwards I had the intermaxillary bone of various animals drawn according to the same in the most definite way; and if such a contribution to the comparative bone theory should be of interest to those in the know, I would not be averse to having a series of these illustrations engraved in copper.
In the cetaceis, amphibians, birds, and fish I have partly discovered this bone, partly found its traces.
The extraordinary variety in which it shows itself in the various creatures really deserves a detailed consideration and will also be striking even to persons who otherwise find no interest in this seemingly arid science.
One could then go into more detail and, with a more precise step-by-step comparison of several animals, proceed from the simplest to the more complex, from the small and narrow to the monstrous and extensive.
What a chasm between the intermaxillary bone of the turtle and the elephant, and yet a series of shapes can be interposed, connecting the two. What nobody denies in whole bodies could be shown here in a small part.
One may overlook the living effects of nature as a whole  and large ones, or one may dissect the remnants of its escaped spirits: it always remains the same, more and more admirable.
It would also give natural history some determinations. Since it is a main characteristic of our bone that it contains the incisors: conversely, the teeth that are inserted into them must also count as incisors. They have been denied Trichechus rosmarus and camels up to now, and I would have to be very mistaken if one could not suit those four and these two.
And so I close this little experiment with the wish that it will not displease connoisseurs and friends of natural science and that it will give me the opportunity to be more closely connected with them in this charming science, as far as circumstances allow, to make further progress.
Galen, Lib. De ossibus. Cap. III.
Campers all smaller writings edited by Herbell. First volume, second piece, pp. 93 and 94. Blumenbach de varietate generis humani nativa, p. 33.
Vesalius de humani corporis fabrica (Basil. 1555) Libr. I. Cap. IX. Fig. II. P. 48, 52, 53
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