88 PEOr. W. K. PAEKEE ON THE STEUCTUEE 



On the Investing Bones displayed in the transversely-vertical sections. 



By going over the figures of these sections in detail, we shall recapitulate what has 

 been said of this system of bones ; the reader will compare these illustrations with those 

 showing the skull in various aspects. 



Section 1 (Plate XVIII. fig. 1). — This is through the forepart of the skull, and shows 

 how the maxillaries (inx) embrace the premaxillary (jjx), especially below ; besides the 

 sharp dentary edges of the former, the upper part of each bone has begun to form the 

 large supracranial valley. 



Section 2. — Here (fig. 2), in front of the outer nostrils (e. n), the maxillaries (mx) are 

 scooped in forming the passage, and are two-winged ; they are crested above, have a 

 ridge below the crest, and are cultrate at their inturned lower edge. The premaxillary 

 (n. px) is now a small wedge between the upper part, only, of the two bones, above the end 

 of the nasal pouches. Below, an oblique wedge of bone is seen ; this is the large left 

 fork of the vomer («) cut through. 



Section 3. — Here (fig. 3) the skull was divided through the nostrils {e. n); and thus 

 the maxillaries {mx) are seen in two parts on each side. The premaxillary (m. px) has 

 thickened again; and the right, or lesser, fork of the vomer [v) is cut through as well as 

 the larger spur. 



Section 4. — In this section (fig. 4), which is also through the nostrils {e. n), the nasals 

 (n) are cut through at their foremost pointed end ; the other parts are closely like what 

 was shown in the last. 



Section 5. — Here (fig. 5), close behind the nostrils, the vomer is cut through behind 

 its notched part ; it is hollow both above and below, and much wider in the latter region. 

 There is here a definite space between the vomer and the inner edge of each maxillary 

 bone {mx) ; and the nasal and intermaxillary wedges {n, npx) are larger. 



Section 6. — In this section (fig. 6) two pairs of new bones are cut thi'ough ; it was 

 made through the widest part of the hinder pouches. The cranial trough is now 

 very large and deep ; for above the maxillaries {mx) a pair of large, solid, obliquely- 

 crested bones have come into view. These are the prefrontals {p-f). The sharp wedges 

 of the nasals and premaxillaries («, n.px) only cover the middle part of the nasal roof 

 {al.sp) ; there is here only a fibrous mat {n.f) over the nasal sacs, rigiit and left. Below, 

 the vomer has given place to the upper processes of the palatines ( pa), which are thick 

 styles : the maxillaries are here thick slabs of bone, sharp above, subcultrate below, 

 and having a sharp process running inwards, the rudiment of a palatine plate. Between 

 the wall and this partial floor the ethmo-palatine {e.pa) is lodged, just as the " pro- 

 rhinal " is lodged between the laminae of the premaxillary in a Batrachian. 



Section 7. — This slice (fig. 7) is from behind the nasal pouches, and also behind 

 the nasals and premaxillaries. Here the frontal (/) comes in at the mid line, and it 

 forms the keystone to a low inverted arch, the piers of which are the large, diverging, 

 sinuous prefrontals {p.f) ; the frontal is here subconvex above and carinate below. 



