RESPIRATION 



151 



Figure 8/. Longitundinal section through the blowhole and diverticula of a porpoise. The 

 dotted line shows the area of the lateral diverticulum. Note the hard connective tissue along 

 the diverticula, the 'plug' (P), and the muscle (M) running from the plug to the top of the 

 skull bones. B = blowhole; D = diverticula ; J = upper jaw bone; J\~ = nasal passage: 



C = brain cavity. 



under the blowhole they have three cartilaginous nasal conchae which 

 are in fact lined with olfactory epithelium. 



In the Mysticetes, the nostrils are in the form of two slits, and the septum 

 is so high up that we are justified in speaking" of two nostrils. The slits run 

 in a sagittal direction converging to form a V with the angle pointing- 

 forward (Figs. 43 and 73). In Right Whales this division is so pronounced 

 that two separate blows emerge, but in Rorquals both nostrils combine 

 to produce a single blow. The openings of the blowhole are surrounded 

 with thick 'lips'. If we climb up a dead whale and try to push our arm 

 into the blowhole, we shall find that a great deal of strength is needed to 

 do so. This is due to the fact that the 'lips' consist of highly elastic tissue 

 which normally keeps the blowhole closed by tension even when the whale 

 is at the surface. To open it during breathing, the whale has numerous 

 muscles which run from the 'lips' to the skull below. Obviously, this method 

 of closing the blowhole is much more effective than the method found in 

 seals, sea-lions and hippopotami whose nosti'ils are normally open and 

 must be closed underwater by an active contraction of annular muscles. 

 Some whales do have annular muscles as well, but they are of minor 

 importance. 



In Sperm Whales, the blowhole is more or less S-shaped, but in other 

 Odontocetes it is a single transverse slit situated right on top of the head 

 (Fig. 50) . Since the front of the skull slopes so steeply, all Odontocetes 

 carry some form of adipose cushion on their foreheads (see Chapter 2 and 

 Figs. 33 and 86), but Mysticetes, whose integument is much closer to the 

 bone, do not possess such a cushion. Where the nasal passage of Odonto- 

 cetes traverses the bones of the skull, it is divided into two by a nasal 

 septum, but no such septum is found in the part of the passage which lies 



