402 SCHULTE, SEI WHALE. 



The lower lip is marked sagittally by a minute furrow. Beginning as an unpigmented line 

 at the symphysis it runs in the intermediate region rather nearer the base than the margin of 

 the lip, here forming the oral limit of the pigment-streak. On reaching the temporal ridge the 

 furrow turns on its mesal surface, eventually ascending slightly to be lost in a depression which 

 corresponds to the orbital triangle of other mammals. Obviously in the post-temporal segment 

 the furrow has ceased to have the significance of a labial or dento-labial sulcus, and it is evident 

 that here an independent element has become secondarily continuous with that furrow. 



The labial sulci diverge for about three fourths of their length and then converge more 

 rapidly. They thus describe curves of lateral convexity and are farthest apart immediately 

 in front of the eyes. In the caudal segment of their course they sweep mesad to the ridge of the 

 temporal muscle and end in a fossa of the roof of the mouth mesal to this muscle and ventral 

 to the orbit (orbital triangle). Lateral to the dental sulci are the low ridges which form the 

 upper lips. These broaden caudad and in the ocular region merge with the convexities which 

 correspond to the under-surface of the eye, and form the roof or upper boundary of the subocular 

 extension of the oral cavity. 



Naso-vomerine organ. At the tip of the rostrum, between the extremities of the dento- 

 labial sulci is situated a small tripartite elevation. It is separated from the surface of the ros- 

 trum by the terminal portions of these sulci, and from the palate by a small transverse furrow 



continuous with the dento-labial. In the median line, the middle 

 lobe of the elevation forms a bridge between the rostral surface and 

 the palate interrupting the sulci, or at least reducing their depth. 

 This portion is triangular with the base caudad. To its sides are 

 attached the lateral lobes, which are reniform, with their concavi- 

 ties mesad. Lateral to them the dento-labial sulci are deepened to 

 little blind pits. They thus are very similar to the structures 

 Fig. 3. Naso-vomcrine organ, described and figured by Weber, 1 and by him interpreted as the 



rudiments of Steno's ducts. In the slightly older foetuses of 



Balcenoptera and of Megaptera, which I have examined, the bounding sulci diminish, the lateral 

 lobes merge into the general relief of the rostrum, and the little pits deepen somewhat, changes 

 which seem to lead up to the conditions described by Lillie. 2 



The flipper. The flipper attains its greatest thickness close to the preaxial border and 

 maintains it for about two thirds of its breadth, the postaxial third being reduced to a thin 

 plate. It is slightly narrowed at its emersion from the integumentary covering of the trunk, 

 immediately distad of the olecranon. From this point it gradually expands for two thirds of 

 its length and then more rapidly tapers to its pointed extremity chiefly at the expense of its 

 postaxial portion. The preaxial border is not quite straight but has an anterior convexity in 

 its third quarter, beyond which the outline has three slight projections corresponding to the 

 interphalangeal joints of digit II. The postaxial border is convex caudad in its proximal two 

 thirds. Its distal third is rectilinear save for a shallow concavity close to the extremity, which 

 gives the tip of the flipper a faintly hooked contour. 



1 Weber, M. Studien ilber Saugethiere. Leipzig, 1885, page 145 and pi. iv figs. 22-24. Cf. also Kuckenthal, Denkschr Merl.- 

 Xat. Gesells. Jena, 1889. 



2 Lillie, D. G. Observations on the Anatomy and General Biology of some members of the larger Cetacea. P. Z. S., 1910. p. 784 

 and text fig. 75. Seo also Burfield, S. T. Belmullet Whaling Station. Rep. Bri. Ass. Adv. Sci., Dundee, 1912. 



