BY PROFESSOR J. T. WILSON. 727 



ill a sulcus in the ventral aspect of the antero-lateral extension 

 of the maxilla. Anteriorly it bends mesially and then sends 

 backwards paramesially a pointed palatine process which reaches 

 a point exactly opposite the anterior blind extremity of the 

 cartilaginous capsule of the organ of Jacobson (fig. 1). 



The hinder end of this palatine process closely skirts the margin 

 of a triangular mesial depression or fovea, which is due to tlie 

 descent of the nasal septum and its appearance in the roof of the 

 mouth (s.7i'), where it merges in the great cartilaginous plate of 

 the snout. This same triangular area is faintly indicated in fig. 

 17, plate xxiii., of Macleay Memorial Vol., illustrating the adult 

 condition of the cartilaginous skeleton as then conceived. In 

 that adult figure it is seen to lie immediately in front of the 

 dumb-bell bone. 



Thus in the young stage under consideration, the palatine 

 process of the premaxilla extends precisely throughout that region 

 where, in the adult, there is no representative whatever of a 

 palatine process of the premaxilla. That this true palatine 

 process of the premaxilla has nothing whatever to do with the 

 production of the dumb-bell-shaped bone is made certain by the 

 examination of the later stage of development illustrated in fig. 7 

 of Model ii. In this the palatine process of the premaxilla still 

 persists, and is of almost exactly the same length as in the 

 previous stage, not having shared in the considerable growth of 

 the surrounding structures. One result of this is that its position 

 has shifted, relative to the cartilaginous roof of the mouth, so 

 that it now no longer extends as far back as the triangular fovea 

 where the septum first appears in the roof of the mouth. It now 

 also falls considerably short of the anterior end of the capsule of 

 Jacobson's organ. This bony process has thus become arrested 

 in development, and no trace whatever of it is to be found in the 

 adult. But already in this stage (Model ii.) the development of 

 the dumb-bell bone has begun in the shape of two small bony 

 splints applied, one on each side, to the ventral aspect of the 

 cartilaginous capsule of Jacobson's organ. These are visible in 

 fig. 17, plate iii., of W. N. Parker's paper in P.Z.S., 1894 (3), 



