TWO SKULLS with ABSENCE of the PREMAXILLA by D

TWO SKULLS WITH ABSENCE OF THE PREMAXILLA By D. E. DERRY Anatomy Department, Egyptian University, Cairo THE condition exhibited by the two skulls to be described is uncommon and for this reason alone it is worthy to be recorded. But it has the further interest that it throws light on the remarkable embryological changes which take place in the development of this part of the face in the human embryo as compared with lower forms. Skull No. 1. This skull was found by Mr G. Brunton in a grave of the 25th Dynasty circa. 700 B.c. while excavating a cemetery on the east bank of the Nile, about 30 miles south of Assiut. The skull appears to be that of a woman and from the condition of the sutures and wearing of the teeth it seems probable that she was well past middle age. With the exception of the deformity to be described the skull is normal. The malformation in question consists in a marked reduction in size of the hard palate and on examination this is found to be due to absence of the premaxillary part of the maxilla as well as the horizontal plates of the palatine bones. Nevertheless the lower margins of the nares and the nasal spine all of which have been believed to be derived from the embryonic fronto-nasal process are well developed. There are of course no incisor teeth, these being developed in the premaxillary element of the jaw. The most centrally placed teeth in this skull should be the canines, but only one of these, the right, is present and it is lying horizontally above the two bicuspids and first molar while its crown is visible just below the anterior nares. The white area seen in PI. I, fig. 1 projecting across the middle line below the nasal spine is the tooth in question. The left canine has not developed, there being no sign of it in an X-ray photograph of the part, but there is an area of bone between the middle line and the socket for the first left bicuspid tooth which represents the site it should have occupied. A minute dental (? enamel) excrescence is present which may be the rudiment of the missing canine. It can be seen in PI. I, fig. 1 lying just to the medial side of the socket for the left bicuspid. Besides the abnormally placed canine tooth only four teeth remain in the jaw (P1. I, fig. 2). On the right side the two bicuspid teeth and the first molar are still present. On the left side the second bicuspid is the only tooth remaining. The condition of the socket for the first left bicuspid tooth indicates that this tooth has only recently fallen out. The socket for the first molar is much absorbed and probably only stumps remained at the time of death. The second 19-2 296 D. E. Derry and third molars have never developed on either side and there is no room for them. Perhaps their absence may be correlated with the non-development of the horizontal plates of the palatine bones. The greatest antero-posterior length of the palate measured from a point on the posterior margin of the socket for the canine tooth to what may be considered as the posterior nasal spine is 26*5 mm. The greatest width measured between the inner margins of the sockets for the first molar teeth is 16-5 mm. From the photograph (P1. I, fig 2) it can be seen that there is extensive (? pyor- rhoeal) absorption of the bone round the roots of the second bicuspid and first molar teeth on the right side and this has proceeded so far that perforation of the floor of the nose at the site of the abscess cavities has taken place. Owing to the extreme smallness of the palate the teeth have failed to articulate properly with those of the mandible which is normally developed and has contained its full complement of teeth. The upper teeth have been caught between the teeth of the mandible (P1. I, fig. 3) and their labial surfaces have been worn flat while the teeth themselves have been pushed upwards and inwards so that, as already said, their roots have come into communication with the floor of the nose. As might be expected, owing to absence of the premaxilla there is no incisive fossa. There is a minute foramen in the middle line immediately behind the abnormally placed canine which may have transmitted the naso-palatine nerves but it cannot be traced to the nose. Further back on the palate is a foramen which opens immediately on the nasal floor and this again may have given passage to nerves or blood vessels or both. Some idea of the appearance of this woman in life is obtained from the profile view (PI. I, fig. 3). Skull No. 2. The provenance of this skull is unknown. From the general appearance and condition of the bones it would seem to be relatively modern. Also it appears to have belonged to an adult woman. Like the case described above, the premaxilla is absent and there are therefore no incisor teeth. The sockets for all the other teeth are present although all of these except the left first molar have fallen out recently. As in Skull 1 the embryonic maxillary processes have grown across the middle line and formed the lower margins of the nares, but they have failed to meet as perfectly as in the first case described, so that the nasal spine is absent and its site is occupied by a depression (PI. II, fig. 4). It is unfortunate that the teeth have been lost as it would have been of interest to have seen whether the canines were normal. In this type of malformation they are the teeth most likely to be affected lying as they do at the junction of the embryonic fronto-nasal and maxillary processes. Actually the sockets left by the canine teeth in this skull are small and shallow, little larger in fact than would be required for milk canines and it is evident that the roots did not penetrate deeply into the jaw. It is possible therefore that the permanent canines had never developed, as is the case on the left side in Skull 1. The socket for the right first bicuspid shows that the tooth was decayed. There has been an abscess at the root which has perforated the alveolar wall. Two Skulls with Absenre of the Premaxilca 297 Both it and the second bicuspid have had insufficient room between the canine and the first molar tooth and are irregularly arranged in consequence. On the left side all the sockets are normally arranged (P1. I, fig. 5). It was remarked in Skull 1 that the horizontal plates of the palatine bones had never been developed. In the skull under review they are normal and the hard palate is correspondingly longer and wider (cf. PI. I, fig. 2). The antero- posterior length from a point in the middle line between the sockets for the canine teeth to the tip of the posterior nasal spine is 400 mm. The width between the second molar teeth is 30*5 mm. The difference between the antero- posterior diameters of the palate in the two skulls, 13-5 mm., is thus almost exactly that of the horizontal plates of the palatine bones, 14-0 mm., which are missing in Skull 1. Although there is no true incisive fossa, this being formed normally between the palatine processes of the maxillae behind and the premaxilla in front, yet the nerves and blood vessels have found their way through the suture between the palatine processes. In marked contrast to Skull 1 in which the smallness of the palate did not allow of normal articulation between the upper and lower teeth, in this second skull although most of the teeth have fallen out it is possible to satisfy oneself that during life the teeth were normally opposed so far as the molars on the left side are concerned, and probably the left bicuspid. This is not so certain for the right side owing to asymmetry of the alveolar arch which has resulted in a crowding of the right upper bicuspid teeth and a tendency for the anterior part of the arch to be pushed inwards (PI. I, fig. 1). While the molars may have articulated, the right upper and lower bicuspid teeth certainly did not. The early disappearance in the human subject of all signs of the suture between the premaxilla and maxilla is a fact of great interest associated as it is with increase in the growth of the brain and recession of the face. Although the suture can be traced on the palate in young and even some adult skulls it has always disappeared on the face long before birth. In the anthropoid apes it persists for many years. If a comparison be made of the associated parts in man and the apes the following remarkable differences will be found. The margins of the nares as seen in man are not represented in the apes. In these animals the corresponding parts are rounded and formed entirely by the premaxilla as this ascends towards the nasal bones. The medial part of each half of the premaxilla slopes steeply towards the nasal floor and passes on to the face without any inter- ruption in the form of a narial margin such as exists in the human subject. Consequently there is no incisive crest and no nasal spine in the apes. Hitherto it has been assumed that in man the whole thickness of this part of the alveolus carrying the incisor teeth and forming the anterior part of the floor of the nose with the margins of the nares and the nasal spine is formed from the premaxilla; but the skulls described above, particularly Skull 1, show that perfect narial margins and a prominent nasal spine may be developed with complete absence of the premaxilla. It is plain therefore that these have developed from 298 9 D. E. Derry the maxillary processes and are a new formation peculiar to man. Frazer, in his Manual of Embryology, p. 275, says: "The maxillary process...as already indicated forms the premaxillary alveolus and the lip, covering the facial aspect of the fronto-nasal process and hiding it completely so that it is not concerned in the formation of the facial surface." Herein lies the explanation of the early disappearance of the suture on the face in the human subject. While such a condition as that described above is rare, malformations in this region of the face are relatively common. They may be ascribed to the fact that the development of this part in man differs in important particulars from that of all other animals owing to the immense increase in the size of the brain, which has resulted in shortening and bending of the cranial base and consequent retraction of the face. These changes are peculiar to man, hence as in other parts of the body where specially human attributes have called for special adaptations, there is a marked tendency for the parts concerned with the newly acquired characters to exhibit malformations.

CONCLUSIONS 1. That the lower margins of the nares with nasal spine and the bone on the face immediately below the spine are exclusively human and overlie the true premaxillary part, thus forming a floor to the anterior part of the nose which is absent in the apes as are also the nasal spine and narial margins. 2. That the growth of this new part which is derived from the maxillary process (Frazer) covers over the nasal portion of the premaxilla, obliterating the suture between it and the maxillary part.

EXPLANATION OF PLATE I Fig. 1. Face view of Skull 1 showing perfectly formed narial margins and nasal spine. The crown of the right permanent canine tooth is exposed below the nasal spine and its root is visible as an elevation of the bone on the front of the maxilla. Fig. 2. To show palate and teeth of Skull 1 with abscess cavities at roots ofsecond bicuspid and first molar. Note absence of horizontal plates of palatine bones, and second and third molars. Fig. 3. Profile view of Skull 1 with mandible in position. Fig. 4. Face view of Skull 2. The union of the maxillary processes has been less complete than in Skull 1. Note absence of nasal spine and cleft in middle line between sockets for canine teeth. Fig. 5. To show asymmetry of palate. Compare with corresponding view in Skull 1. Note presence of palatine bones and sockets for all molar teeth. Fig. 6. Profile view of Skull 2 and mandible. Journal of Anatomy, Vol. LXXII, Part 2 Plate I

Fig. 1. Fig. 2. _i=_...... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... ~~~~~~~~~~~~~~~~~~~~...... ;.1

3. F Fig -Fig..6. 4.-

Fig. 5. Fig. 6.

DERRY-Two SKULLS WITH ABSENCE OF THE PREMAXILLA.