BY W. J. McKAY. 897 



quadrilateral, the antero-posterior being larger than the lateral 

 axis. The anterior border runs from within outwards and back- 

 wards. Where the internal two- thirds joins the external third, a 

 peculiar process of bone projects which fits into a niche in the 

 premaxilla, which will be more particularly described later on. 

 The external third is concave, and forms portion of the supraorbital 

 ridge. The posterior border is convex and articulates with the 

 parietal ; it has, however, no connection with the postorbital as in 

 Pyflion. This border is bevelled from before downwards and 

 backwards, and fits in between the under portion of the anterior 

 edge of the temporal and of the anterior edge of the lateral plate ; 

 thus a firm schindylesis is formed. The internal edge joins its 

 fellow of the opposite side in the mid-line, a distinct frontal suture 

 marking the junction. Anteriorly a plate of bone projects down- 

 wards vertically and meets the lateral plate in the mid-line. Thus 

 by the two sides joining, a vertical septum of bone is formed, 

 which separates portion of the cerebral hemispheres. The superior 

 surface is quadrilateral, convex and subcutaneous. The lateral 

 part of this bone consists of a plate that runs from the middle of 

 the inferior surface downwards and in wards, meeting its fellow of 

 the opposite side in the mid-line, where they lie on tlie parasphenoid. 

 The external surface of the lateral plate is concave and smooth, 

 and joins with the orbitosphenoid and the anterior portion of the 

 lateral plate of the parietal to form the large orbital fossa for the 

 eye and lachrymal gland. A notch in the posterior border of the 

 lateral plate is portion of the optic foramen. 



The frontal articulates with the parietal, parasphenoid, orbit- 

 sphenoid, premaxilla, and nasal bones. 



Os POST-FRONTALE VEL POST-ORBITALE, 



Zygomaticum vel Frontale posterius, D' Alton; Frontale posterius, 

 Cuvier, Harting, Stannius ; Post-frontale vel Post-orhitale, Gegen- 

 baur, Parker, Parker and Bettany ; Post-frontale^ Huxley, Hoff- 

 mann, Wiedersheim ; Schuppe des Schlafheins^ Meckel; Frontale 

 posterius vel Orbitale poster ius, Joh. Miiller, Owen. 



