98 “TERRA NOVA” EXPEDITION. 
occur beneath the blubber of the throat-groove region in Balaenoptera, were also 
present in Megaptera. 
When the coat of blubber was removed from the carease of a whale, the 
more superficial muscles had a tendency to come away with the blubber. These 
muscles were confined to the ventral anterior three-quarters of the animal, in the 
regions occupied by the throat-grooves and the mammary glands. (See text-fig. 7.) 
There appeared to be two pairs of superficial muscles in the throat-groove 
region; the anterior pair may possibly be the mylohyoid, and the posterior pair 
may represent the pectoralis major. Delage,* who described these muscles in 
Balaenoptera physalus Linn., regarded the anterior pair as modified superficial 
muscles of the neck. He mentioned that the fibres of the muscles were arranged 
more or less longitudinally in B. physalus, but in Megaptera they were oblique. 
The probable function of the superficial muscle in the mandibular region is to 
diminish the mouth-cavity, after each mouthful, by the contraction of its floor. 
Delage suggested that the function of the posterior superficial muscles might 
be to compress the air in the lungs, after each act of inspiration, in order to render 
the animal heavy enough to sink without effort. The Right Whales and the Sperm 
Whale float on the surface of the sea after they are shot, whereas the Balaenopteridae 
tend to sink. The latter family have ventral grooves and an associated system of 
muscles, which are absent in the former types. It is possible that the contraction 
of the ventral superficial muscles, after death, presses the air out of the lungs, and 
so causes the Balaenopteridae to sink. The elasticity of the ventral body-wall in 
these whales would allow of a great expansion of the lungs after inspiration, 
which would make the animal so light that “ sounding ” would be difficult, unless 
it could alter its density at will by means of the muscles of the ventral grooves. 
The superior mechanism for increased lung-capacity and the regulation of density 
which seems to be possessed by the Balaenopteridae, lend some support to the 
widespread belief that they are capable of remaining under water for a longer 
period than other whales. 
I made further inquiries of whalers as to the length of time it was customary 
for the Balaenopteridae to remain below water, and was given to understand that 
the Humpback rarely remained under water for more than a quarter of an hour 
between each two acts of respiration. Seven minutes was considered to be the 
normal interval between each two breaths in this species. 
The belief, which is held by some whalers,t that the larger Balaenoptera can 
remain below the surface for twelve hours, was discredited by those whom I met in 
New Zealand. The latter were of opinion that the Balaenoptera were never in the 
* Delage, Y., Arch. Zool. Exp., 2 Sér., Tome IIT. 3 bis, 1885, pp. 29-38. 
+ Andrews, R. C., ‘“‘Monographs of the Pacifie Cetacea,” Mem. Amer. Mus. Nat. Hist., New 
Series, Vol. 1, Pt. V., 1914, p. 256. 
t Lillie, D. G., Proc. Zool. Soc., 1910, p. 790. 
