738 COMPARATIVE ANATOMY 



THE TONGUE 



The tongue varies to a very considerable extent in the different 

 groups of vertebrates (Fig. 432). In mammals the hyo-branchial sup- 

 port consists simply of a basi-hyal (body) and two pairs of horns 

 (cornua). The most cephalad pair are the longer and usually consist of 

 four bony structures, the cerato-hyal, the epi-hyal, the stylo-hyal, and 

 the tympano-hyal, the latter bone attached to the skull in the tympanic 

 region. The pair of horns lying caudal consists of only a single skeletal 

 piece of bone known as the thyro-hyal which connects the body with the 

 thyroid cartilage of the larynx. In the human being, the anterior or 

 cephalad horns are considerably modified from those in other mammals. 



The tympano-hyal and the stylo-hyals have fused with the otic re- 

 gion of the skull to form the styloid process, while the hypo-hyal is a 

 mere rudiment connecting with the styloid process by a ligament; the 

 cerato-hyal is not present. The anterior horns, though typically 

 longer and more complex than the others, are called the ''lesser" in man, 

 because the earlier anatomists took all of their names from the human 

 being without any comparisons with other forms. 



There is no functional tongue in fishes, although the material which 

 develops into a tongue in the higher forms is present. This is known as 

 the anterior part of the hyo-branchial apparatus. The part of this com- 

 plex apparatus lying most cephalad, is found in the floor of the mouth 

 cavity. It is naturally shaped according to the outlines of the jaw which 

 border it. It may even be pushed forward so as to form a slight eleva- 

 tion by the action of the visceral muscles. 



In amphibians where the gill-bearing function has more or less 

 ceased, this region forms the basis of the tongue, while a fleshy organ of 

 some kind may develop. 



In the higher forms of vertebrates two to four of the visceral arches 

 form the skeletal basis of the tongue. The hyoid arch is the structural 

 foundation to which the muscles of the tongue are attached. Here one 

 usually finds, although there are many varieties, a median basi-branchial 

 piece called the os entoglossum and two caudad projecting horns the 

 cornua. In Sauropsida the tongue is a direct condition of this, and the 

 principle motion consists in protruding and withdrawing the entire organ 

 by means of the two caudal horns which lie in sheaths from which they 

 may be everted. The tongue is sometimes quite long and then the 

 sheaths and the enclosed horns are, of course, of corresponding length. 

 If they are very long there must be some disposition made of them when 

 retracted. This is interestingly observed in the salamander Spelerpes 

 fuscus, where the sheaths of the horns run down the sides of the body 

 until they are attached to the pelvic bones, the ilia. In the woodpecker 

 they pass around the occipital region over the top of the head and end 

 near the anterior nares of the base of the upper beak. In such cases the 



