AN OS INTERFRONTALE BY EDITH F. WILLOCK, M.B.

THHE following instance of a large os interfrontale, present in a living male infant of two and a half months, is of interest. The metopic suture in this case was widely open and the interfrontal bone was situated in the resultant interval between the frontal bones, and extended upwards into the anterior fontanelle. The bone was leaf shaped, closely resembling the epiglottis in outline and its narrow inferior extremity could be traced to the angle of union of the frontal bones, l*5 cm. from the nasion, and* appeared to be united to them at this point; the superior extremity encroached on the anterior fontanelle, but did not extend as high as the line of the coronal suture. The bone measured 4-5 cm. in length and its maximum width, approximately at the juncture of the upper and middle thirds of its long axis, was 2 cm. An X-ray photograph showed this bone to be circular in shape and entirely separated from the frontal bones, but this appearance was due in all probability to its incomplete ossification: there was no evidence of more than one centre of ossification. The anterior fontanelle was large, the dis- tance from its posterior angle to the superior extremity of the os interfrontale being 5 cm. while its maximum width was 6 cm. and the width at the upper limit of the interfrontale bone was 3 cm. The skull was slightly dolichocephalic \ (cranial index 74.3) and was cryptozygous. The lamboid suture was open and a definite space intervened between the margins of the occipital and parietal bones; this was most marked on the left side and was confirmed by the X-ray picture. The X-ray also showed ? NAT. that the margins of the coronal suture on the C right side were not in apposition. In other Fig. 1. Diagram of anterior fontanelle respects the skull appeared normal and there and interfrontale bone, drawn to was no evidence of hydrocephalus. scale. A, anterior fontanelle; B, The infant, which was admitted to the interfrontal bone; C, nation. Manchester Babies' Hospital as a severe case of marasmus, was very wasted Qn admission but improved slowly under prolonged treatment. The eyes 440 Edith F. Willock somewhat approached the Mongolian type and both lower lids showed a slight degree of entropion. Both ears were malformed as regards the helix, antihelix and antitragus. Pulmonary, cardiac and abdominal examination revealed nothing abnormal. No family history of importance was obtainable and there were no brothers or sisters. Le Double (Traite des variations des os du crtne de l'hnomme, Paris, 1903) has collected the literature on the subject of interfrontal bones and has added

Fig. 2. To illustrate the position of the interfrontal bone. (A photograph of the skull of an infant on which has been painted the outline of the anterior fontanelle and interfrontal bone as in the case described.) to this the result of his own series of cases. Ile states that there are three types of os interfrontale: (1) the os nasofrontale, situated in the region of the nasion; (2) the os mediofrontale or metopique, which lies in the metopic suture at the juncture of its middle and lower thirds (Staderini, quoted by Le Double, found this type to be present in *3 per cent. of his series); (3) the os bregmatique, situated in the region of the bregma, which was found in *6 per cent. of all skulls examined. The os bregmatique possesses many other synonyms, varies widely in size and shape, and attains to greater dimensions than either of the other two types. According to Le Double, this bone may be divided horizontally in the plane of the coronal suture and either portion An Os Interfrontale 441 may exist alone; should the bone lie below the coronal plane it is termed infrabregmatique (interfrontal), if above, suprabregmatique (interparietal). Wormian bones are frequently associated with the presence of hydro- cephalus and in this case the possibility of the latter condition was suggested by the state of some of the sutures; there was, however, no hypertension of the fontanelle and no other signs or symptoms were present, so its absence was presumed. There is some doubt as to which class of interfrontal bone this case should belong. Its large size is in favour of its being considered an os hemibregmatique (infrabregmat que), and at first sight the X-ray findings support this view, as the only ossified area shown is in the region of the upper extremity of the bone. Clinically, however, the bone is in intimate relation with the metopic suture and is apparently united at a low level, 1-5 cm. from the nasion, with the frontal bones, while its upper extremity barely reaches the position of the anterior angle of a normal fontanelle. Remembering that the X-rays merely show the existing area of ossification and are no true criterion of the actual extent of the bone, the evidence would seem to indicate that this case is in reality one of an os metopique of exceptionally large dimensions. I am indebted to Dr Catherine Chisholm for permission to publish this case.

Anatomy Lix2 29