676 MAMMALIA. 



developed in the lower Vertebrata, have therefore totally disap- 

 peared ; and the question to be solved is, how we may identify the 

 remaining portions with any of the elements of the more complex 

 structures that have come under our notice. 



(755.) Difficult as this would be to the student who had con- 

 fined his attention to the human body, on referring to the os 

 hyoides of a quadruped, one of the Carnivora for instance, the 

 analogies become at once perceptible. The body (jig- 315, a) 



is evidently the representative of the 



J . Fig. 315. 



central portion of the hyoid apparatus 



in Fishes (Jig. 221, 42), in Reptiles 

 (fig. 260, 5), and in Birds (fig. 271). 

 The lingual elements found even in 

 birds are quite obliterated ; but two 

 arches still remain. The posterior of 

 these (fig. 315, <f), which represent 

 the larger cornua of the human os 

 hyoides, do not reach the cranium, but, 

 as in Man, are attached by muscle and 

 ligament to the thyroid cartilage ; 

 while the anterior cornua, so small in 

 Man, are in quadrupeds by far the 

 largest, each consisting of two pieces, 



of which the second are articulated with the extremities of the 

 styloid bones (c, c), and these last are in turn joined to the tem- 

 poral bones by means of articulating surfaces. In Man the styloid 

 bones (c) become anchylosed with the temporal, giving rise to the 

 i( styloid processes ;" and the intermediate pieces of the anterior 

 cornua (b) have their places supplied by ligaments (the stylo- 

 hyoid) : in this way, therefore, the hyoid apparatus attains the 

 form that it exhibits in the human skeleton. 



(756.) The muscles connected with the os hyoides in quadru- 

 peds correspond with those met with in the human body ; and 

 their action in effecting the deglutition of food is well known to 

 the anatomical reader. 



(757.) The passage of the fauces in the Mammalia presents an 

 organization peculiar to the class, and exhibits structures adapted 

 to prevent alimentary materials from entering the air-passages 

 during the operation of swallowing. The most remarkable of these 

 is the epiglottis, forming a valvular fibre-cartilaginous lid, that 

 accurately closes the opening of the larynx during the transit of 



