DE. J. MU1UE ON THE "WHITE-BEAKED BOTTLENOSE. 117 



the superficial margin is lined with dark pigment, and swept 

 round by wrinkles. Eversion of the lips shows a cup-shaped spi- 

 racular cavity, on the anterior wall of which are two smooth- 

 surfaced oval prominences meeting in the median line so as to 

 form a Y-figure ; and these are connected by a strong fibrous 

 septum to the posterior wall. They represent the alar fibro- 

 cartilages. 



The anterior or premaxillary sac extends forwards 2 6 inches 

 in front of the orifice of the blow-hole ; or if the latter be in- 

 cluded, and a post-extension of the spiracular cavity freely com- 

 municating with it, the measuremeut gives 4*4 inches in extreme 

 length. The sac is slipper-shaped, as is common to the group ; 

 near its point it is | of an inch in width, and expands behind to 

 1| inch. The interior mucous lining is pale-coloured and smooth- 

 surface ; but there is an appearance of submucous venous vascu- 

 larity at the outer and inner margins. 



The maxillary or upper lateral sac is, as usual, flask-shaped, and 

 but 2 inches deep. What I have elsewhere* denominated the 

 naso-frontal sac (the posterior sinus) burrows backward for ^ an 

 inch, and reaches forwards for as much. Its interior was in part 

 choked up with a greasy-like firm mucous substance. 



The muscles of the forehead and nasal region of Lagenorhyn- 

 chus are in layers like those of PhoccBna, Grampus, and Glohio- 

 cephalus ; but the difference in shape of the bony areas necessi- 

 tates variation in the extent of the fleshy attachments. Com- 

 pared with the latter round-snouted genus, the upper layer in the 

 "White-beaked Bottlenose reaches more anteriorly in front of the 

 eye — in fact, is continued on to the end of the maxillary or cheek- 

 process of bone. The manner in which it is fixed to the blow- 

 hole aperture shows that its fibres have power chiefly on the 

 upper wall of the maxillary sac; at the same time the muscle, 

 being fixed in front and behind the blow-hole, must act as a 

 complete dilator of the orifice when all the fibres act simulta- 

 neously. 



The second layer is stronger than the superficial one. To- 

 wards the blow-hole it is very aponeurotic. From being radially 

 attached round the outer wall of the maxillary sac, apparently it 

 acts as a tensor of this cavity, whilst through it and by a direct 

 attachment of fibres fore and aft it influences dilatation of the 

 blow-hole. What particularly attracted my attention was the 

 * Camb. Journ. of Anat. and Physiol, vol. v. p. 125, fig. 1. 



