LEPIDOSIREN. 167 



upper and lower jaws, in each of which the plate is divided at the 

 middle or symphysial line so as to form two distinct lateral teeth. 



The intermaxillary bone is represented by a single, horizontal, 

 triangular plate, the base of which is attached by ligamentous union 

 with the frontal and ascending process of the palatine bones, 

 upon which it enjoys a slight vertical movement ; the rounded apex 

 forms the anterior extremity of the skull, and it is at the under 

 surface of this part that the two laniariform teeth are attached 

 by ligaments proceeding from their base, so as to admit of a yielding 

 motion in every direction for a small extent, but most resisting 

 inflection outwards. Their office is to pierce and retain the nutritive 

 substance which is afterwards divided and comminuted by the strong 

 maxillary dental plates. 



The upper pair of these plates is supported by the anterior 

 part of a strong arch of bone which combines the characters of 

 the superior maxillary, palatine and pterygoid bones : the superior 

 maxillary is represented by the external process which pro- 

 jects outwards and backwards and terminates in a free point on 

 each side of the anterior part of the arch ; the palatine portion con- 

 stitutes the median and anterior part of the roof of the mouth ; the 

 pterygoid portion is indicated by its fulfilling the usual function of 

 an abutment extended between the palatine portion of the upper 

 jaw and the articular pedicle of the lower jaw : the upper dental plates 

 are confined to the first two parts of the arch and do not extend upon 

 the pterygoid portion ; the lower dental plates are anchylosed to the 

 premandibular bone. Viewing the upper pair of plates as a single 

 tooth, it may be described as being indented at its outer surface by 

 five vertical angular notches, penetrating inwards through half the 

 breadth of the supporting bone, and dividing the plate into six 

 angular processes, which, from the direction and varying form and 

 breadth of the entering notches, radiate from the posterior part of 

 the median line or division of the tooth (PL 59, fig. 3). The inferior 

 dental plate is similarly notched on its outer side, but the propor- 

 tions of the angular indentations are such that they receive the 

 processes of the upper dental plate when the mouth is shut ; thus 

 the median notch is wider than the two adjoining ones in the lower 



