HEARING 



211 



A 



Figure 1 1 1. A 



B 



C 



the bulla of a Rorqual as whalers remove it from carcasses. B andC 

 they shape it without and with the eardrum. 



how 



which latter is also considered as part of the petrosal (the mastoid process). 

 In Mysticetes, the tympanic is attached by two, and in Odontocetes by 

 only one, very thin, tongue-shaped bone process to the other two bones, 

 and therefore breaks off very easily. It is a shell-shaped bone surrounding 

 a greatly enlarged swelling of the tympanic cavity, which gives it a 

 bladder-like appearance - hence the name bulla tympani, or bulla for 

 short. 



It is this bulla which whalers have the habit of taking home with them 

 as souvenirs, not for their biological interest, but because their strange 

 shape so oddly resembles a human face. A small process forms the nose; 

 eyes, ears and a few locks of hair are painted and, straight away, you have 

 a model of a friend's or relative's face or, if your tastes run that way, a 

 caricature of some political figvue. If the long projection of the eardrum 

 (see above) is not cut off, the figure looks as if it were smoking a cigar, 

 like Churchill or Sibelius (Fig. 1 1 1). 



The petrosal is an extremely hard bone close to the opening of the 

 bulla, and may be compared with the petrous portion of the temporal 

 bone of man and other mammals. It surrounds the cochlea and the semi- 

 circular canals of the inner ear, which will be discussed below, and has 

 two processes (the proötic process and the mastoid process, also called the 

 mastoid bone) by which it is joined to the other bones of the skull. Of 

 these two processes, the mastoid is the more important. In Odontocetes it 

 is short, rather flat and broad and attached by two ligaments to the 

 squamosal and occipital bones of the skull. In Sperm Whales, the process 

 is somewhat more highly developed and is mainly lamellar in structure, 

 and in Mysticetes it is a long, knotted bone which fits tightly between the 



