| OCR Text |
Show 234 . MR. H. O. FORBES ON T H E [Feb. 28, inch wide (measured on the upper surface). In the older specimen (F) in the Otago Museum the maxillary ceases at 7*65 inches, and in the type (K) at 9| inches from the apex of the rostrum, so that the groove practically ceases there. The lower flange of this groove is generally traceable on the side of the rostrum much more clearly than the upper, and in older specimens is very pronounced at the base of the rostrum, decreasing in prominence as it runs forward, especially in the Kaiapoi specimen (I) and iu M. australis, Flower. The depth of the groove and of its subtu-bercular pit, and the divergence of its flanges, appear to vary with age and sex, and would seem to be dependent on the individual growth of the bones in the neighbourhood, especially the increase forward of the palatines and pterygoids. In those forms in which the buttress is strongly developed, a shallow depression or groove separates the lower flange from the maxillo-pterygoid swelling. Seen from the palatal surface. From this aspect the relations of the palatine and pterygoid bones in the two Otago Museum specimens (A, F), in the three Canterbury Museum examples (H, I, K ) , and in Al. grayi of Flower's paper in the Society's Transactions are identically the same. The palatines lie on the outside of the pterygoids, reaching forward as far as but not extending beyond their pointed ends; the pterygoids, therefore, articulate directly with the maxillaries. In the M. (Oulodon) grayi figured by Van Beneden the palatine bones completely •surround the anterior ends of the pterygoids and extend anteriorly to them, preventing their coming into contact with the maxillaries. The same differences exist between the specimen in the Canterbury Museum of Ziphius cavirostris, in which the palatine bones surround the pterygoids, aud the figure on plate xxi. bis in the ' Osteographie' of Van Beneden, in which they do not. The same differences were also pointed out above in m y remarks on specimens of M. layardi, and are therefore due solely to individual variation. The relations of the premaxillaries, maxillaries, and vomer on this aspect of the cranium are the same in all .these specimens, the amount which each contributes varying with the age, sex, or individual. The number of teeth in the gum of the upper jaw in the examples I macerated, in one case exceeded by one, in the second case was less by one, and in the third equalled that given by Sir Julius von Haast in describing the type species. The triangular pterygoid in all these examples has the usual everted lower border and deep fossa, as also the deep notch at the base of the pterygoid plate, and presents no essential feature by which the species can be separated one from another. The pterygoid fossse in the three specimens I dissected contained each a large air-sac opening into the ear-cavity, and communicating with the mouth by the Eustachian passage. In M. grayi the pterygoid fossa never extends anterior to the level of the maxillary tubercle. |
