160 HISTORY OF THE HUMAN BODY 



only in a few amphibians, and then mainly during larval life, 

 and are otherwise modified to assist in the functions performed 

 by two organs that develop in the region, the tongue and the 

 larynx. The latter makes its appearance in a very simple 

 condition, associated with two bag-like lungs, in the most 

 primitive of the salamanders, and utilizes as the first laryngeal 

 cartilage, cartilago laieralis, the last of the gill-arches (5th 

 branchial or 7th visceral arch). This element, which, by sub- 

 division and metamorphosis, develops into a pair of arytanoid 

 cartilages and a series of lateral tracheal pieces, shows itself 

 capable of becoming a complicated mechanism, sufficient for 

 the needs of amphibians; but in the reptiles the 4th gill-arch 

 (6th visceral) becomes associated with it as the epiglottis, 

 which here appears for the first time. The reptilian larynx, 

 with but little modification, is employed by the birds, but in 

 mammals the next two gill-arches, counting anteriorly, the 

 2nd and 3rd (4th and 5th visceral) become associated together 

 in front of the larynx and form the protecting shield-like 

 piece, the thyreoid, which in the lowest Order (Monotremata) 

 still appears like two pairs of arches covering the larynx 

 ventrally. 



It may be said in general that in all the Classes, from 

 the amphibians on, those visceral arches not employed as 

 jaws or as laryngeal cartilages form a hyoid or hyo-branchial 

 complex and furnish a skeletal equipment for the tongue, an 

 organ which often develops voluminously, fitted for very spe- 

 cial work. Thus, in the amphibians in general this complex 

 consists of the 2nd to the 6th visceral arches, inclusive; in 

 reptiles and birds of the 2nd to the 5th, and in mammals of 

 the 2nd and 3rd only. In the latter these two remaining 

 arches form a complex consisting of a median piece, 

 the basi-hyal, and two pairs of cornua, the anterior pair 

 representing the 2nd visceral arch, the true hyoid of fishes 

 and the posterior pair the 3rd visceral or ist gill-arch. In 

 most mammals the anterior cornua of this hyoid complex con- 

 sist of a chain of small bones, which, enumerated from the 

 basi-hyal ("body of the hyoid"), are: cerato-hyal, epi-hyal, 



