1901.] AXATOMT OF COGIA BBEVICEPS. Ill 



Turning our attention to the posterior cleft on the floor of the 

 vestibule, it is seen to be a groove between the convex floor (valve) 

 and the hinder lip of the blowhole (d), which here bends suddenly 

 downwards to form a vertical Avail to the vestibule : on pressing it 

 backwards, a horizontally disposed furrow (g) is seen about half- 

 way down — a furrow which is about \ inch deep and nearly co- 

 extensive with the length of the wall ; it appears to be connected 

 with the working of the lip itself. At the extreme right corner 

 of the cleft is the small entrance to the right narial canal, having 

 the form of a horizontal slit, about ± inch in length, bounded by 

 smooth, inconspicuous lips (fig. I). The " spiracular sac," or 

 vestibule, then receives both right and left narial canals, which 

 are extremely disproportionate in size and are very different in 

 structure. 



The left narial canal being the more conspicuous, and having a 

 simple course, may be considered first. From the vestibule it 

 passes outwards for a brief space, and then abruptly downwards 

 with a slightly inward bend towards the median line, to reach the 

 bones of the facial region of the skull ; it passes through these to 

 open into the naso-palatine canal. The " valve " which was seen 

 in the vestibule is continued throughout the entire length of the 

 canal as a well-marked convex, typhlosole-like ridge on its mesial 

 wall, and is visible at the lower opening of the canal into the naso- 

 palatine canal (PI. VIII. fig. 5 ; PL IX. fig. 9). 



This left narial canal, then, is quite simple ; but it is otherwise 

 with the right canal, which is complicated bj r the existence of a 

 couple of dilatations to form " spiracular chambers," similar to 

 those occurring in the Delphinidse, from which, however, they 

 differ in two or three particulars. 



The right " nostril " is a small slit-like orifice bounded by thin 

 muscular lips ; it leads into a short canal which passes across the 

 middle line, obliquely forwards, downwards, and to the right. It 

 terminates in a considerable chamber, but on its way gives rise to 

 branches that pass towards the left, and subdivide to form a number 

 of narrow, anastomosing tubules, lying in front of the left narial 

 canal (PI. IX. fig. 9, n). 



The chamber, or upper chamber (A) as it may be called to 

 distinguish it from a second one lower down, is irregularly ovoid 

 in shape, with its longer diameter transversely disposed ; this 

 longer axis measures about 5 inches ; its shorter axis, or height, is 

 3 inches. The chamber is situated immediately below the Hbro- 

 lnuscular dermis, and is lined by a smooth, greyish membrane : its 

 wall is not muscular, and relatively thin, though it is embedded in 

 I he muscles of this region. 



Its roof is formed of a series of trabecular having, in general, a 

 transverse direction ; these, by lateral branches, connect with one 

 another, so as to Bonn a kind of network, leaving shallow pits 

 between the trabecule. Some of these are deeper, and lead into 

 shorl CBBcal tubes projecting backwards ; whilst lower down <>n the 

 hinder wall are a lew Larger, circular apertures leading into similar 



