128 INTRODUCTION. 



windpipe, is a continuation : the Eustachian tube, which leads to the in- 

 ternal ear, enters it on each side; and the two posterior nares enter 

 above. 



The anterior portion of the mouth is roofed above by the true 

 palate, and bounded by the teeth of both jaws. The skin of the palate 

 is firm and tough, with a longitudinal ridge down the centre, and marked, 

 more or less, by transverse ridges and furrows. In some animals, as 

 the Rabbit, &c., these ridges and furrows are very numerous and 

 distinct. The floor of the mouth is occupied by the tongue, an organ 

 which exists in all Mammalia, varying, however, in shape and extent 

 of mobility : in general, it is broad, long, and rounded at the apex : it 

 is composed of muscles, and is based upon a peculiar bone, termed 

 the os hyoides (from its shape, which is supposed to resemble that of 

 the Greek v, upsilon). This bone consists of a body, or central por- 

 tion, and of lateral appendages, termed its cornua, which are continued, 

 by cartilage, to the basal part of the temporal bone. 



The os hyoides varies greatly in figure, and in the proportions of its 

 parts, throughout the whole of the Mammalia ; and in a group of Ame- 

 rican Monkeys, termed Howlers (Mycetes), this bone presents a most 

 remarkable dilatation of its body, in the form of an enormous oval drum, 

 with thin osseous walls ; through an opening into 

 this drum passes a membraneous sac, distended with 

 air from the larynx ; and the vibrations of the air, 

 during the loud cries of these animals, are communi- 

 cated to the osseous case of the membrane, which acts 

 as a sounding board. (Fig. 130, represents the dilated 

 os hyoides of one of these species.) 



yj In the Cetacea a principal feature of the os 



o Lyoid, of Howling hyoides is its want of connexion with the larynx, 



Moukey. m conse q uence o f the elevated position of this tube. 



The tongue is essentially composed of muscles ; which are either 

 proper (that is, not inserted into the os hyoides) or common (that is, 

 inserted into the os hyoides, or the lower jaw). Of the first series, 

 the greater number are in pairs ; that is, the same on each side : in the 

 Carnivora, there exists a bundle of cartilaginous fibres, enclosed in a 

 sheath, and running down the centre of the under surface of the tongue : 

 its form is worm-like ; and, indeed, it is known by the name of " the 

 worm." In the Dog, Cat, and Bear, it is very conspicuous : Blumenbach 

 has detected it in the Opossums, and Carus in the Mole. By its elas- 

 ticity it serves to give vigour to the movements of the tongue ; but, in 

 the Dog, it has been ignorantly regarded as the cause of rabies, or, at 

 least, as favouring the reception of this disease ; and hence it is often 

 cruelly torn away. 



