The phenomena of dentition before the period of cutting are these; the jaws of the fœtus are closed the whole length of their upper edge; they appear to be homogeneous at first view; but examined in their interior, they exhibit a row of small membranous follicles, separated by delicate partitions, disposed like the teeth of which they are to serve as the germ, and having the following arrangement.

The membrane which serves as a covering to the follicle forms a sac without an opening, which lines at first all the parietes of the socket, to which it is attached by elongations. At the place where the vessels and nerves enter, this sac leaves the socket, becomes detached, is folded into the form of a canal which accompanies the vascular and nervous bundle, and afterwards spreads out upon the marrow of the tooth which is the termination of the bundle.

It follows from this that this membrane has the general conformation of the serous membranes, in the shape of some kinds of night-caps. It has two portions, the one attached and lining the socket, the other loose and covering the marrow, as for example, the pleura has a costal and a pulmonary portion. The marrow and the vessels, though contained in its duplicature, are in truth found without the cavity, which is lubricated by a simple exhalation. I have found that this exhalation was like that of the serous membranes, essentially of an albuminous nature; the action of the nitric acid, that of alkohol and of fire incontestably prove it. Subjected to the action of one of these agents, especially the first, the membrane whitens immediately. The layer of albumen which covers it becomes concrete and coagulated, as when we make a similar experiment upon a serous surface.

The marrow, very considerable at this period, is found suspended, like a bunch of grapes, from the extremity of the vessels and the nerves.

It is upon the medullary portion of the membrane of the follicle, and upon the surface of its loose extremity, that the first osseous point is developed; it soon extends, and takes precisely the form of the top of the crown, which it is afterwards to form, that is to say, that it is quadrilateral in the molar teeth, pointed in the canine, and wedge shaped in the incisors. Developed at first nearest the gums, it extends afterwards along the vascular and nervous stem, it is moulded upon it as it approaches the part of the alveolus where it enters; so that it exhibits on this side a concave surface which embraces the pulpy portion of the membrane, and adheres by several vascular elongations; and as this portion is loose, the first rudiment of the tooth floats also in the cavity of the membrane, as we can see very well by cutting the alveolar portion of this membrane, after having destroyed the corresponding part of the alveolus.

The following consequences result from this kind of development; 1st. The crown is first formed, and the root is not produced but as the ossification in length advances upon the portion of membrane lining the vascular and nervous bundle. 2d. As all the vessels that come to the tooth enter at its internal surface, and as the external is entirely free in the cavity of the membrane, the ossification in thickness is made especially at the expense of the internal cavity which is constantly contracting, as well as the marrow, an arrangement, the reverse of that of the other bones, the ossification of which commences at a point placed in the centre of the cartilage, and which at first solid in the middle, afterwards become hollow for the medullary cavities and those of the cells, which are always enlarging. 3d. After the ossification of the tooth, the portion of the membrane of the follicle which lined the alveolus, remains the same, whilst that its portion corresponding with the marrow, originally free at the other side, becomes adherent on this side to the whole dental cavity which it lines, of which it forms the membrane noticed above in the article on the structure of the teeth, and which is thus found between the marrow and the osseous substance. 4th. The marrow of the tooth is the part first formed, and the most considerable in the first periods of life. It appears that the osseous substance is next formed, and that the enamel afterwards arises on the exterior of this. I have not yet been able to make evident the manner of its origin.

It is difficult to ascertain at what period the membraneous follicle is formed; that of the first ossification appears to be from the fourth to the fifth month. At the time of birth, we find the twenty teeth of the first dentition already advanced; the whole crown is formed; the beginning of the root appears also in the form of a broad tube, with extremely delicate parietes, and which is constantly becoming longer and thicker; when it reaches the bottom of the socket, the tooth immediately appears externally as this is too narrow to contain it.

The number of teeth, less in the first than in the second dentition, gives a peculiar form to the jaws of the fœtus and the infant, especially to the lower one, which is less elongated in front, and consequently wider in proportion than in the adult, in whom in order to receive all the teeth, the alveolar border must necessarily be more extended. This arrangement of the lower jaw has a great influence in the expression of the physiognomy.

First Dentition considered at the period of Cutting.

The following phenomena take place about the sixth or seventh month after birth, very rarely sooner, still more rarely before birth, though there are examples of this, as is proved by the history of Louis XIV. At first the two small incisor teeth of the lower jaw appear, sometimes together, sometimes separately; soon after the corresponding incisors of the superior jaw. A month or two later, the four other incisors are cut. At the end of the first year, the four canine teeth usually appear. At the end of the second, or often later, two molar are cut in each jaw and two others soon follow. Each cutting almost always begins in the lower jaw. At the age of four years, four and a half, sometimes five or six, always at a very uncertain period, there appear below two other molars and then two above, which complete the number of twenty-four teeth forming the first dentition; all these except the last four fall out and are replaced by new ones.