MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 313 



leading to the rich diploe of the light, expanded, articular portions of the jaw. Several 

 other pneumatic holes lie in the deep smooth concavity between the articular facets ; 

 and there is here and there a larger passage of the same nature on the internal face of 

 the broad part of the ramus. The posterior angle of the jaw is half an inch below and a 

 little behind the external articular facet ; this angle is tubercular, and soon loses itself 

 in the strong convex inferior margin of that flat, crescentic, smooth end of the mandible, 

 the inner extremity of which has been described above. This broad end of the man- 

 dible, which passes a little forwards as well as inwards, is IJ inch in extent ; and here 

 the two inner angular processes of the opposite rami are only two-thirds of an inch 

 apart. The large vascular foramen (inferior dental) is within, and half an inch behind 

 the highest coronoid part of the jaw ; it has a tubercle for muscular attachment close 

 above it, another behind, and another still larger on the external margin, one-third 

 of an inch external to it. The smooth, rounded, narrow inferior edge of the hinder 

 part of the mandible, at 1^ inch from the end, swells out and rises gently, becoming 

 again slightly carinate as it nears the external angular process. 



Subjoined is a Table of comparative measurements showing the length of the man- 

 dible measured along the curve, and the extent of the coalesced symphysis, in different 

 birds, in inches and lines (or twelfths of an inch) ; also their proportion to each other. 



We see by the above table that the symphysis, in the Common Goatsucker, is twice 

 as long, in proportion to the length of the jaw, as in the Pelican, and that the Boat-bill 

 is four and a half times as strong at that part of the jaw, whilst the Balaeniceps has 

 just ten times as much symphysis as the Pelican. Buceros bicornis is quite without a 

 peer in this part of its anatomy, although the Parrots come very near it. The relative 

 length of the dentary portion of the mandible to the entire ramus is another very 

 important point in the anatomy of the Bird's head ; for, as a rule, the strong horny 

 sheath reaches to the posterior end of this element of the mandible. 



In the next table the length of the mandible is put into parallelism with the extreme 

 .length of the dentary, which overlaps the articular moiety of the ramus at its posterior end. 



