OF THE CETACEA. 63 



valve, which may be compared to an epiglottis, 

 and which prevents the entrance of foreign bodies. 

 The skin over the valve is scarcely two lines thick, 

 but internally it envelopes a projecting body, which 

 is about two inches thick, and which is composed 

 of a network of tendinous fibres hard as wood, and 

 \vhich can scarcely be cut with a knife. A similar 

 network of tendinous fibres, arranged in circles, 

 forms, in this situation, the external wall of the 

 blowing canal ; and two strong muscles rising from 

 the frontal bone, and peculiar to the canal, acting on 

 these bodies, most effectually shuts them down, and 

 thus secures the canal. It is an apparatus to which 

 there is nothing similar in any of the other mam- 

 malia. We shall, on this interesting point, likewise 

 avail ourselves of the interesting descriptions and 

 sketches of Scorseby. In the true whale, he remarks, 

 the first impression of each blow-hole on the upper 

 part of the skull is marked by an oblong cavity 

 (see 1, sketch L Plate i. representing the upper sur- 

 face of the anterior part of the whale's skull, the 

 skin and fat being removed), which is the seat of a 

 muscular substance attached by its anterior extremity 

 to the surface of the skull, and also attached by its 

 posterior and inferior extremity to the interior of 

 the skull, at some depth in the blowing canal 1, 1, 

 sketch m. The part of this muscle which pene- 

 trates the bony canal is of a conical form, the apex 

 downwards, or within, represented at 2, in figure 

 #i, which is a vertical section of the skull ; so that 

 when this interior portion contracts, the muscular 



