152 WHALES 



in the adipose cushion, or in the blowhole. Just where the nasal passage 

 emerges from the skull, the adipose cvishion sticks out over it like some sort 

 of plug and forms a narrow passage which may be completely closed 

 during respiratory intervals (Fig. 87). The plug can be pulled forward by 

 means of a powerful iTiuscle attached to the bones of the snout, and the 

 passage is thus widened. Above this plug are found the peculiar diverti- 

 culae (or air pockets) mentioned earlier, which extend to the top, to the 

 back and to the side of the adipose cushion. While the diverticulae 

 themselves may be fairly wide, their openings into the nasal passage are 

 generally very narrow. Their shape and position differs from species to 

 species but the principle is the same in all Odontocetes, with the exception 

 of the Sperm Whale, which has a single diverticulum between the 

 spermaceti cushion and the skull, and another anterior to the cushion. 

 This is shown clearly in Fig. 33. The diverticula of the Odontocetes are 

 not equipped with special muscles, but are partly surrounded by a very 

 characteristic layer of particularly tough and non-elastic connective tissue. 

 According to Kiikenthal (1893), some sections of the diverticulae still 

 show traces of an olfactory mucous membrane. It is his contention that 

 the species in which these traces occur also have olfactory nerves at an 

 early stage of their embryonic development. A number of other zoologists 

 have tried to solve the problem of the function of the diverticula, including 

 Cuvier himself, who thought that they served to remove water which had 

 accidentally entered the nostrils. Since, however, no special muscles are 

 attached to the diverticula, this explanation sounds improbable, and the 

 same can also be said of many other theories which have been put forward 

 during the past 150 years. From the recent and very thorough research 

 work of Lawrence and Schevill (1956) it is clear that at least one of the 

 diverticula, i.e. the lateral, does in fact act as a plug for the blowhole. 

 These two scientists not only made a profound study of the structure of 

 diverticula in Common Dolphins, but also in the Bottlenose Dolphins of 

 the famous Marineland aquarium in Florida. Their project was financed 

 by the American Office of Naval Research, evidently in the hope that their 

 research might have useful applications in the naval field. It emerged 

 that the animals could seal off their blowholes most effectively by blowing 

 air into the lateral diverticula. Moreover, Lawrence and Schevill dis- 

 covered that this plugging effect was by no means their only function, and 

 it seems feasible that the diverticula form a part of the valve system of 

 Odontocetes, a hypothesis first put forward by Raven and Gregory in 

 1933. The simultaneous occurrence of diverticula and epiglottal 'beaks' 

 in Odontocetes and the absence of both in Mysticetes points clearly to the 

 conclusion that these two structures must be interrelated in some way. 

 If this is so, it is possible that during fluctuations in pressure the air from 



