CETACEA—LILLIE. 99 
habit of staying below for more than one or two hours at most. This estimate would 
tend to coincide with the period arrived at by Kiikenthal * on the following ingenious 
line of argument. The normal interval between each two respiratory acts in man is 
three and one-third seconds ; in the pearl-diver this interval can be extended to one 
and a half minutes ; the normal interval in whales is seven minutes; therefore, by rule 
of three, the interval in Balaenoptera can be extended to three hours. Whales which 
can swim under water for two or three hours would easily evade the most vigilant 
whalers, and lead the latter to suppose that their quarry had gone below for a 
whole day. 
MovEMENT OF THE Lower Jaw. 
Some years ago Mr. Lydekker noticed in a skull of Balaenoptera borealis, Lesson, 
that when the mouth was closed the rami of the lower jaw appeared to be turned 
upwards and inwards, whereas when the mouth was open they were turned down, so 
that the convexity became outwards instead of upwards. 
In order to test this observation in a fresh specimen, and to ascertain if it 
occurred in the case of the Humpback, I persuaded the whalers at Whangamumu to 
open the mouth of a freshly killed whale, which measured forty feet in leneth, by 
fastening a noose round the snout and raising the upper jaw by means of the winch. 
When the jaws were closed the rami of the lower jaw fitted closely against the 
edges of the upper jaw throughout its entire margin, so that the blade of a knife could 
not be inserted between the lips at any point. 
As the mouth was opened, I distinctly saw the convexity of each ramus turn 
slightly downwards and outwards, causing the width of the space, enclosed by the two 
rami, to increase. This action of the rami of the lower jaw, in the process of opening 
and closing the mouth, is well illustrated by the rim round the mouth of an ordinary 
hand-bag. When the bag is fully open, it corresponds to the lower jaw of a Whalebone 
Whale whose mouth is wide open. Close the bag rather less than a quarter, by raising 
each side some fifteen degrees from the horizontal, and it gives an idea of the position 
of the rami when the whale’s mouth is completely closed. 
Before permittmg the mouth of the whale upon which I was experimenting to 
close, the masseter and temporal muscles were severed in order to keep the lower jaw 
in the position which it had taken up when the mouth was open. The upper jaw was 
then lowered upon the mandible, and a space of one and a quarter feet occurred on 
each side between the inner edges of the mandible and the outer rim of the beak. 
(See text-fig. 5, A). 
Thus, when the mouth was open, the width of the space between the rami was 
shown to be increased by two and a half feet. 
* Kiikenthal, W., Denkschr. med. naturw. Gesellsch. Jena, Bd. TIT., Theil 2, 1893, pp. 312-317. 
t True, F. W., ‘“‘ Whalebone Whales of the Western North Atlantic,’ Smithsonian Contributions to 
Knowledge, 1904, Vol. XXXIII., Pl. 41, figs. 1, 2 and 4. Liouville, J., op. cit., Pl. IV., fig. 2. 
