stage, no one who is familiar with the practical evidence at the present day would seriously challenge the fact that from this stage onward the story is perfectly clear. That is Professor Osborn's great contribution to the study of the history of the teeth-that he assembled so much evidence; and there is also so much evidence in this museum which is not yet published, in many families and orders of mammals, tending to show that the tritubercular type is the real startingpoint of such diverse molars as, for example, a carnassial, flesh-cutting tooth on the one hand, and a crested herbivorous tooth on the other. I said nothing about the origin of the tritubercular type, because until we get more remains of mammals during the Age of Reptiles, we cannot say whether the inner or the outer cusp is the older, which is really the chief point at issue between the two different schools of paleontologists.

Secondly, as far as I can see, the correlation of upper and lower teeth is much closer and more rigid in types with an orthal jaw motion, as in some of the carnivora. That is, there is not so much opportunity for variations in the exact relations between the parts of the upper and lower teeth; every point in the lower must fit in one corresponding space or depression in the upper series; but where there is a side swing there is room for a great variety of patterns, and there is also considerable variation both in the precise placing of the cusps of the upper and lower teeth, so that possibly the orthodont relations between the cusps is much more exact in some individuals than in others.

In studying the orthodont relations of the teeth of Eocene lemurs I have found that when the lower teeth sweep across the upper there is more chance for certain parts to slide across each other; for example, in one animal a certain lower cusp (entoconid) articulates a little lower down on the internal cusp of the upper molar, and in another a little farther up. Therefore I venture to ask you, as specialists, whether the human type, with its comparatively flattened crown and milling jaw motion, may not have

wider range of possible orthodont relations than in such animals as have a rigid orthal motion, as in the carnivora?

The PRESIDENT. It is seldom that we have upon the same occasion two lectures of such great value as we have had this afternoon, and I shall be pleased to entertain a motion of thanks to Dr. Gregory and Mr. Sullivan.

Dr. HELLMAN made such a motion, and it was carried unanimously. The meeting then adjourned until 8 P.M.

EVENING SESSION.

The evening session was held at the Museum of Natural History, the president, Dr. Murlless, calling the members

to order at 8.30 o'clock.

The PRESIDENT. The next order of business is a paper "On Healthy and Diseased Conditions of the Alveolar Processes of the Jaws," by Dr. A. HOPEWELL-SMITH, Philadelphia, Pa.

[This paper is printed in full at page 426 of the present issue of the COSMOS.]

DISCUSSION.

Dr. Wm. K. Gregory. I would like to ask Dr. Hopewell-Smith about a certain point shown in one of his slides. It showed a basal cingulum on the molar teeth of the hyæna. That is a structure of great interest to the paleontologist, because the cingulum is very characteristic of the teeth of the most ancient mammals, and it is very likely that the ancestors of many living groups once possessed strongly developed cingula in both the upper and the lower molars, and that later the cingulum became atrophied, and in man has nearly disappeared. In man Carabelli's cusp seems to represent the remains of the cingulum, as shown in primitive types of human molars and in the chimpanzee. I would like to ask Dr. Hopewell-Smith what his idea would be as to the function of the cingulum in the hyæna, and also as to its minute structure.

Mr. L. R. Sullivan. Dr. HopewellSmith's paper was highly instructive. I was especially interested in his remarks on the degeneration of the molar series in modern man, and the statement that the incisor teeth are usually the last to be lost. I am wondering whether or not Dr. Hopewell-Smith can throw any light on that condition of the molar teeth known as "taurodontism." This condition is characteristic of the Neanderthal and Heidelberg molars. The roots of the teeth are shorter and less distinct than in Homo sapiens. Should this character be regarded as a specialization or a retrogression?

I

Dr. Milo Hellman. What I am particularly interested in, and what I think should be of interest to most orthodontists, is the question of the effect of anemia and hyperemia upon the tissues involved in orthodontic operations. think this question has a great bearing on the degree of response obtained during treatment. Dr. Hopewell-Smith has made it clear that under anemic conditions bone absorption is enhanced. It would therefore, account in many instances for the perverse conditions brought about in response to the mechanical stimulation by means of the orthodontic appliance. This is one point of value in the paper that has a direct bearing upon our work.

Another point is the question of hyperemia. I did not quite get the essayist's idea of its influence upon the bone changes occurring during treatment. I think, however, that it has an intensifying effect upon the calcification of the bone. If that is so, the bone would not be as responsive to pressure as normal bone.

A further statement of interest is the one Dr. Hopewell-Smith made with regard to the resorption of bone with age. If I understood him correctly, he said the absorption is not interstitial. should like him to explain that. I have seen sections of long bones, as well as of jawbones, which show that with the increase of age the thickness and number of bone spicula in the spongy bone portions decrease; for instance, the head of the femur in a young person has a great

many more and stouter spicula than that of an old individual; in the young the spicula cover a larger area than in the old, but with the increase of age the number of spicula decreases. What is true of the long bones is also true of the cancellous portions in the jawbones. If this is so, would it not constitute interstitial resorption of bone?

With regard to the intensification of the bone portions situated between the roots of the molar teeth of anthropoid apes, I would like to ask whether the essayist has observed similar sections of the same species in young individuals, and whether the tissues are of different texture. For instance, I have in mind the orang.

The orang dentition shows

a considerable amount of wear at an early age. The wear of the teeth in the upper jaw, for instance, is at the expense of the lingual cusps of the premolars and molars. In proportion as this is manifested by the teeth the apical two-thirds of the buccal roots of the molars become denuded, and are visible through the external plate of the alveolar process.

I would therefore ask Dr. HopewellSmith to tell us if he has observed any such sections of the same species in the young before the projection of the roots occurs, and if the bone tissue situated between the molar roots is of a like texture in the young as observed in the adult animals.

It would seem that the dense bone tissue referred to by Dr. Hopewell-Smith is the buccal plate of the alveolar process after such change has taken place in the Identition of the ape.

Dr. H. C. Ferris. I want to thank Dr. Hopewell-Smith for his excellent. presentation of the question. I want to ask a question or two in reference to pathological findings pertaining to our work. One is, whether he has noticed any differential pathological picture radiographically in osteomyelitis in other parts of the body than in this region of ours?

Another practical point is: We frequently have radiographic records made of cases that we are working upon, and find a very much thickened area in the region of the teeth under continuous

movement. Those pictures are often diagnosed as pathological, due to infection. At the completion of our work, that tissue seems to be rebuilt and gives a normal radiograph. If you would explain to us the histological process as compared with the pathological, I think it would be of great interest.

Dr. B. W. Weinberger. I desire to ask Dr. Hopewell-Smith his opinion concerning the absorption of the roots of teeth. This was not quite clear in his paper just read. He mentioned the noneruption of laterals, but failed to state the cause of absorption of deciduous molars where there were no premolars to take their place. Is it the vitality of the bone structure, or is there some other explanation as to the cause of absorption?

Dr. Frank Gough. Along the same line Dr. Weinberger has spoken of, I would like to first state that in my observation of radiographs, there have been many cases in which the roots of the deciduous teeth would be absorbed, and in others they would not. Even in the same mouth, an upper second deciduous molar on the right side, which was not succeeded by a permanent tooth, had fully formed roots and no absorption whatever, while on the opposite side the roots were entirely absorbed, and there was no bony attachment whatever.

Dr. B. W. Weinberger. In line with my first question and extending the question asked by Dr. Gough, we find a great many cases where either the anterior or posterior roots of a deciduous molar will absorb and the other roots of the same tooth will remain normal, thus preventing the premolar from erupting. Has the essayist any explanation to offer for these phenomena ?

Dr. Hopewell-Smith (closing the discussion). In regard to the question of Dr. Gregory, I think I might say that the structure of the cingulum is probably very much like an anatomical condition found in the deciduous teeth. The deciduous molars, for example, possess constricted necks below the enamel. There is a special bending there of the dentinal tubes, and I believe, although I have not examined particularly the cingulum of the hyæna, that we should

find the same condition there. No doubt the presence in a deciduous molar of a rather prominent cervical edge of enamel acts as a preventive of injury to the succeeding tooth. In relation to the second premolar in man, probably the internal cusp may be an elevation of the end of the cingulum. That is an interesting point, but not thoroughly determined.

A question was asked as to the late retention of the mandibular incisors in a certain picture I showed on the screen. I have not examined the jaw microscopically, but I believe the alveolar process is retained, because of its resemblance to compact bone elsewhere. There would seem to be a condition of the bone here which has a different structure from other portions of the alveolar process.

I should regard bone absorption as a retrogressive step. I think it must be considered so, because I am of the opinion that the teeth themselves are degenerate as well as their sockets. Man is anatomically a degenerate being.

Dr. Hellman asked about hyperemia. There is not very much known about its effects on the subject under discussion, because there are not sufficient data. We can only surmise that anemia favors absorption, and hyperemia, I think I said, favors a consolidation of the bone. If it remains a hyperemia, well and good; but if it goes on to an acute inflammation, an absorption of the alveolar processes occurs at the same time. It is not quite clear which is better-anemia or hyperemia; both are bad.

Osteo

There is simply a change in which the medullary spaces become enlarged, and the bone becomes osteoporous-thinner and fragile and breaks easily. porosis is frequently found in old people who have been bedridden for years, and even the moving of the person from one bed to another may cause the fracture of, say, the femur because of that condition. Patients in hospitals frequently have fractures of the femur from just that

cause.

As far as I know, the sockets are very closely allied in man and the anthropoid apes. I have not studied that point very extensively.

Dr. Ferris. At the present time, the study of pathological conditions in mouths being treated by the general practitioner is being severely criticized by the medical fraternity at large; they are trying to put the burden of infection upon the dentist. The medical man is also closely observing the orthodontist, and once in a while, when examining mouths where there are a dozen pictures taken, for instance, of one jaw, he finds conditions in the region of our work which appear to be a thickening of the area, and immediately marks that as a pathological area. Then he immediately asks us for an explanation. In several instances I have claimed that the condition was due to a normal-or rather a traumatic disturbance due to the pressure of my apparatus. The slow, continuous pressure I believe has set up a minute multiple fracture in all the lacunæ of the bone, and I think that was the cause for the thickening shown in the picture. After the case has been retained and functions restored for six or eight months, other pictures have been taken, and they show the region cleared up. I would like to know whether I was right or wrong in my conclusion.

Dr. Hopewell-Smith. I think with a slow movement you are causing a hyperemic condition of the parts. You also get probably some hyperplasia of the parts. You do not mean rarification?

Dr. Ferris. No; where absorption has taken place, of course there is a rarefied area.

Dr. Hopewell-Smith. My opinion is that it is exceedingly difficult to tell just what is going on there. You may see an area where the rays pass through more clearly, and that may be an alveolar abscess, a dental cyst, or a sarcoma. I had a case of a man with a fractured maxilla, which was properly treated. An X-ray was taken. Six weeks after, when union was established, another X-ray photograph was taken, and showed no formation of callus, in spite of the fact that it existed. We have not yet learned to always interpret X-ray photographs correctly.

Dr. Ferris. If pressure is applied to a root, is a hyperemic condition stimu

Dr. Ferris. In cases of arrested development, or sclerosis, we determine by the X-ray whether the process was underdeveloped, or whether it was natural.

Dr. Hopewell-Smith. I do not think I can enlighten you further on that.

In regard to the question about absorption, someone asked why the tooth. should remain longer on one side than on the other. I think it depends largely on the vitality of the tooth. If it is a "dead" tooth, I do not think it absorbs as readily as a vital tooth, and the fact of the tooth being vital or devitalized I think would account for the absorption of one root and not another. At times part of the pulp may die, and part of it remain vital; and when absorption is going on, the part containing the vital tissue would absorb much more readily than the other part which was not vital.

I am sorry I have not been able to clear up all the questions, but I thank you very much for your kind attention.

Dr. HELLMAN moved a vote of thanks to Dr. Hopewell-Smith for his very excellent paper. The motion was unanimously carried.

Dr. HELLMAN also moved that the secretary write a letter of thanks to the president of the Museum for the very courteous treatment accorded the society. The motion was carried.

Dr. LAWRENCE BAKER of Boston then showed a number of lantern slides of skulls illustrating the harmonious relation between arch form and head form, after which the society adjourned.