THE DEVELOPMENT OF THE HUMAN MAXILLA, VOMER, AND PARASEPTAL CARTILAGES. By Professor FAWCETT, M.D., University of Bristol. THE usually accepted descriptions of the development of the maxilla of man state that it arises by a number of separate centres-the number varying somewhat with the authority, likewise the situation of these centres. No description of the maxilla can be considered complete unless at the same time notice is taken of the manner of development of the premaxilla, which, of course, forms the anterior segment of the adult bone as usually interpreted. But the consideration of the development of the premaxilla may be left until that of the maxilla has been fully dealt with. Before breaking new ground, it may be well to state what are the usual statements with reference to the ossification of the maxilla. These statements are apparently for the most part based on work done by Callender, Toldt, Rambaud and Renault, and Bland Sutton, so far as concerns human anatomy. More recently Franklin Mall has given his views on the subject in the American Jouarnal of Anatomy, views based on observation of specimens treated by the "clearing" method of Schulze. So far as they go, these statements are in harmony with my own notions, which I have for several years now taught. A very precise account is given in Cunningham's Text-book of Anatomy. The maxilla is there stated to be developed in the connective tissue around the oral cavity of the embryo from centres which are not preceded by cartilage, of uncertain number, as early fusion takes place between them. They appear during the second month of fetal life, shortly after the clavicle has begun to ossify, and by the sixth month are so united that their independent character is obscured. Five centres are described, viz.:-An external or malar, which forms the bone to the outer side of the infra-orbital canal; an inner or orbito- nasal, from which is developed the inner part of the floor of the orbit, the frontal process, and the wall of the antrum; a palatine, for the posterior three-fourths of the palatine process; a nasal, situated between the frontal process and the canine tooth. Then an incisive centre is added to form the premaxilla; finally mention is made of a centre described by Rambaud The Human Maxilla, Vomer, and Paraseptal Cartilages _F and Renault, which is wedged in between the incisive and palatine elements beneath the vomer, explaining the Y-shaped arrangement of the foramina of Stenson which open into the anterior palatine canal. This is the sub-vomerian centre of Rainbaud and Renault. or the centre of Huschke, and, it will later be seen, belongs really to the premaxilla. The account given in Gray's Anatomy varies a little from the foregoing. The malar centre is described as giving origin to that part of the bone external to the infraorbital canal and to the zygomatic process; the orbito- nasal forms that part of the body internal to the infraorbital canal, includ- ing the inner part of the floor of the orbit and the citer wall of the nasal fossa; the palatine gives rise to the palatine process behind Stenson's canal, and to the adjoining part of the nasal wall; the premaxillary forms the front part of the alveolus which carries the incisor teeth; the nasal gives rise to the frontal process and the portion above the canine tooth; the infravomerine lies between the palatine and premaxillary centres and beneath the vomer. These various centres appear about the eighth week, and by the tenth week the bone consists of two portions, one the maxilla proper, and the other the premaxilla. The suture between the two portions persists on the palate till middle life, but is not to be seen on the facial surface because, according to Callender, the front wall of the sockets of the incisor teeth is not formed by the premaxillary bone, but by an outgrowth from the facial part of the maxilla proper. The view adopted in Quain is similar to the above of Gray, Callender and Sutton being quoted in evidence. Gaupp, in Hertwig's Handbuch, describes the maxilla as arising from five centres, and quotes Toldt as finding five centres which appear at the end of the second month and the beginning of the third. These towards the end of the fourth month blend together and with the os incisivum. (1) An independent centre for the lateral part, together with the lateral half of the orbital surface and the lateral wall of the alveoli of the molar teeth. (2) A second for the medial hinder part of the body and the medial half of the orbital surface. (3) A third for the facial surface over the canine tooth and the frontal process. (4) A fourth for the palatine process, the medial lamella of the alveolar process, and the anterior part of the nasal surface of the body. (5) A fifth (doubtful) for the region of the sulcus and the crista lacrymalis. Gaupp then states that, according to Mihalkovics, the upper jaw incorporates into itself the paranasal process of the nasal capsule, and that also during the fourth to fifth month small cartilaginous nuclei appear in the alveolar part without any connection with the nasal capsule and later becomes incorporate with the upper jaw. Keibel and Mall incline to the view that the maxilla proper develops 380 Professor Fawcett from one centre only, and adduce in support Hertwig's model from an 80 mm. embryo. (This statement is clearly based on Mall's paper in the American Journal of Anatomy, which has been before alluded to, and perhaps one here might state generally what Mall found. He states that the maxilla in his specimen arises from two centres, one to form the maxillary bone proper and one to form the premaxilla. In one of the youngest specimens, 16 mm., the maxilla is marked by a mass of granules, together I mm. in diameter, lying spread out just beneath the eye and 1 mm. from the middle line. In another specimen, of 18 mm., the maxilla is absent, but the premaxilla, measuring i mm., is present. In another specimen of the forty-second day both centres are present. At a later stage the bones are denser, and both have parallel processes which no doubt are to form the frontal process. At the fifty-sixth day the two bones are found united along the alveolar border, but the processes are separate for a long time. At no time are more than two centres present, and these unite in the very beginning of the third month. The numerous centres described by Rambaud and Renault, Mall attributes to breaks in preparing the specimens.) In a footnote in Keibel and Mall's Embryology, Le Double (1906) is quoted as giving the number of centres as described by various authors including the incisoria as: One-Camper, Rousseau, Cleland; two-Jamain; three-Serres, Meckel, Cruveilhier; five-BNclard, Sappey, Leidy, Poirier, W. Krause; five or six-Portal; six-Rambaud and Renault; seven -Weber. Hunmphry (1858), who is very accurate in his statements concerning ossification, doubts the real existence of more than one centre for the maxilla proper. In a footnote he states: " There are many fissures which extend to some depth in the fetal and young bone; but we must not think that these are necessarily the indications of its having been developed from several centres." (The italics are mine.} J. Bland Sutton describes the maxilla as consisting of four distinct portions. a. The premaxillaryregion in relationwith the ethmo-vomerine cartilage; b. a prepalatine portion forming a platform for the support of the anterior end of the vomer; c, a maxillary centre situate to the inner side of the superior maxillary division of the fifth nerve; d, the malar piece, lying outside this nerve and supporting the malar bone. Three figures are given in illustration of these statements. In another page by the same author, an extraordinary figure is given of a three months' embryo, in which a bar of cartilage is represented as passing from the malleus region to the inner side of the maxilla. How such figure was arrived at, it is difficult to say. The Human Maxilla, Vomner, and Paraseptal Cartilages 381 From the above statements it is clear, first, that there is a doubt as to the manner of ossification of the maxilla, secondly, that we are divided between a one-centred and a many-centred origin for the maxilla proper. The object of this part of this communication is to show that the maxilla proper arises from one centre of ossification only, unless, as appears to be the case, the paranasal process be regarded as ossified independently. The conclusions which I have arrived at are based on exhaustive examination of sections with the microscope, models reconstructed from these sections, specimens cleared by the Schulze method, and dry specimens of various ages. Personal Observations. The maxilla proper commences as a membrane bone on the outer side of the nasal capsule, and above the canine-tooth germ. In point of time one may say that, SQ far as the microscope reveals, it commences to ossify about the 18-mm. stage. (Mall, who claims greater delicacy for the Schulze method, shows in his table that several embryos of 15-mm. length have an ossified maxilla. I have never observed it at that stage.) So far as my experience goes, it is preceded in ossification by both the clavicle and the mandible. But the mnaxilla is not wholly a membrane bone; it is added to, as Mihal- kovics has stated, by periosteal cartilage along the alveolar wall-in the rabbit, Fuchs has observed a hyaline cartilaginous nucleus at the hinder part of the palatine process near the inner alveolar wall-and by incorpora- tion of that cartilaginous offshoot of the lateral nasal wall which Mihal- kovics has termed the paranasal process.