1. That in cases of alveolar harelip, a small portion of bone has been found in many instances on the outer side of the cleft, quite distinct from the maxilla. This is claimed to be the mesognathion, separated by the cleft from the endognathion, and by a distinct suture from the exognathion. A picture (Fig. 39) is appended of an adult skull taken from the museum of the Royal Anatomical Institute of Kiel, which clearly shows a small distinct flake of bone in the required position, extending back as far as the ordinary site of the anterior palatine canal. Such has been also found in children’s skulls, and very distinctly in a series of horses’ skulls with alveolar harelip. (For figures of such, _v._ ‘Langenbeck’s Archiv,’ xxxi, 2.) But this condition, indicating the distinct entity of the mesognathion, is not very commonly to be demonstrated in human pathology, inasmuch as the suture is early obliterated. But its existence is indicated by the dentition, to which we must now turn. [Illustration: FIG. 40.—Drawing of a case of double alveolar and palatine cleft with projecting os incisivum, to show the lateral incisor on outer side of the cleft. _i₁_, _i₂_, _c_, _m₁_, _m_₂, represent the alveoli of the teeth as in Figs. 26 and 27. _v._ Vomer. B. Palatal process of superior maxilla united to the meso- and exo-gnathion. A. Os incisivum, consisting of the two endognathia, and bearing the alveoli of the central incisors. (After _Albrecht_.)] 2. That in alveolar harelip there is in a large number of cases a distinct precanine or incisor on the outer side of the cleft. This is well shown in Figs. 39 and 40. In the former, an adult skull, the mesognathion is distinctly seen bearing the alveolus of a precanine tooth, the lateral incisor; whilst the central bony portion (the endognathion) bears but the socket for one tooth, the central incisor. The latter is a picture of a child’s skull with double alveolar harelip and cleft palate; the os incisivum is seen separate and projecting forwards at the end of the nasal septum; it bears the sockets of the two central incisors. Outside the cleft the alveolus bears four teeth on either side, viz. two molars, one canine, and one precanine, which we cannot but recognise as the normal lateral incisor. So that the dental formula of the upper jaw might be represented thus: In normal jaw—CI₂I₁I₁I₂C; in double alveolar harelip— CI₂=I₁I₁=I₂C,