6 THE VOYAGE OF H.M.S. CHALLENGER. 



much more spongy character. The surface of section through the beak approximated 

 in shape to a heraldic lozenge, the inferior angle of which was rounded (PL I. fig. 6). 

 In specimen 5 the mesorostral bone terminated Gj inches from the tip of the beak, 

 and anterior to it the beak was hollowed into a deep furrow covered over by a dense, 

 fibrous membrane. 



In the younger skull, the inner borders of the preemaxillfe were parallel and close 

 together in the anterior half of the beak, but diverged somewhat posteriorly. In 

 both crania these bones ascended behind the base of the beak to form the sides of the 

 anterior nostrils, and to terminate at the vertex in a roughened overhanging ridge. 

 The anterior surface of the ascending part of each bone was concave from above down- 

 wards, and the outer and inner borders were concave in the same direction ; the con- 

 cavity of the inner border added to the width of the nostrils, the greatest transverse 

 diameter of which in the younger skull was 2-^ inches, in the adult 2^ inches. The 

 prajmaxiUse were a-symmetrical at their nasal ends, the right being not only wider, but 

 higher than the left, so that the nasal openings were directed to the left. The a- 

 symmetry was slightly more marked in the adult than in the younger skull. On the 

 anterior surface of each prsemaxilla a large foramen was situated a little behind the 

 antorbital notch. 



The nasal bones were laterally compressed and placed vertically between the two 

 praemaxillae. The upper border of the right was, in both crania, broader and more j)ro- 

 jecting than the left. The mesethmoid nasal septum was inclined obliquely to the left ; 

 in the adult its free border was sharp in the greater part of its extent, but below it was 

 prolonged into the mesorostral bone. A deep depression was, however, situated at their 

 place of junction, which indicates, I think, that the mesethmoid and mesorostral bones had 

 originated from separate centres of ossification. In the young skull it was from 5^ to ^ 

 inch broad, and had the roughened surface characteristic of a bone to which ossifying 

 cartilage had been attached. 



The spout-like vomer formed in the young skull the floor and in part the sides of the 

 mesorostral furrow to within 3^ inches of the tip of the beak, where it terminated in a 

 pointed end ; j)Osteriorly, in both crania, it articulated with the sides of the mesethmoid, 

 and, expanding laterally, was jointed with the under surface of the body of the sphenoid. 

 The vomer appeared in the hard palate of the 5^ounger skull, as a mesial fusiform bar of 

 bone, nearly 5 inches long, situated between the superior maxilla and prsemaxilla of opposite 

 sides. In the adult, the rostral part of the vomer was concealed by the mesorostral bone, 

 except on the palatal surface, where it appeared as a mesial fusiform bar, about 11 inches 

 long. In both crania, the vomer also appeared on the surface as a slender mesial bar 

 between the two pterygoid bones ; in the adult, 85 inches were seen, extending back- 

 wards between these bones ; but in the young skull, scarcely an inch in length of the 

 vomer appeared, where the pterygoids diverged from each other anteriorly. 



