792 



MAMMALIA. 



Fig. 401. 



smaller appendages, called the lesser cornua, are articulated with the 

 upper surface of the hyoid bone, close to the point of junction between 

 the cornua majora and the body, from whence ligaments, called the 

 stylo-hyoid, pass upwards and backwards to the styloid processes of the 

 temporal bone. 



(2298.) All the apparatus of hyoid arches passing between the body 

 of the bone and the base of the cranium, which were so largely deve- 

 loped in the lower Vertebrata, have therefore totally disappeared ; 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. 



(2299.) Difficult as this would be to the student who had confined 

 his attention to the human body, on 

 referring to the os Jiyoides of a quadru- 

 ped, one of the Carnivora for instance, 

 the analogies become at once percep- 

 tible. The body (fig. 401) is evidently 

 the representative of the central portion 

 of the hyoid apparatus in Fishes, in 

 Reptiles, and in Birds, which have been 

 described in preceding pages. The lin- 

 gual elements, found even in Birds, are 

 quite obliterated ; but two arches still 

 remain. The posterior of these(fig.401), 

 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, and these last are in turn joined to the temporal 

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

 become anchylosed with the temporal, giving rise to the " styloid pro- 

 cesses ;" and the intermediate pieces of the anterior cornua 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. 



(2300.) The muscles connected with the os "hyoides in quadrupeds 

 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. 



(2301.) 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, 



Os hyoides. 



