528 LOUISE SMITH 



response to the necessity for a changed mode of respiration and 

 a changed diet at that time, an anatomical description of the 

 apparatus associated with these phenomena may be of interest. 



It is of course the hyobranchial skeleton which supports the 

 external gills of the larva and its muscles that move them in 

 the many varied and characteristic ways. The first basibranchial 

 and ceratohyals also support the very primitive larval tongue, 

 which is merely a fold in the mucous membrane filled in with 

 connective tissue and scarcely more pronounced than the lateral 

 oblique folds in the floor of the mouth that are an adaption to 

 the movement of the gill arches. Whatever motion this larval 

 tongue, so like that of the fishes, is capable of, is also brought 

 about by the hyobranchial muscles. 



With the loss of the external gills at metamorphosis, the 

 function of the visceral skeleton as a support for the organs of 

 respiration is minimized, though its muscles still bring about the 

 characteristic movements of the pharynx that accompany bucco- 

 pharyngeal respiration. Its main purpose now seems to be to 

 support and move the very specialized tongue which has devel- 

 oped for capturing and disposing of the more rapidly swimming, 

 jumping and flying prey of the adult. The adult tongue is a 

 mushroom-shaped organ capable of a great variety of motion. 

 Its stalk is formed by the basibranchial cartilage and the pair of 

 abdominohyoideus muscles, and its very glandular disk is 

 supported by the tip of this basal piece and associated cartilages 

 and regulated by fibers of the hyoglossal muscle (fig. 2). It is 

 capable of being withdrawn wholly into the mouth, with the 

 disk parallel to the stalk, and the mucous membrane of the 

 latter folded back like a semi-inverted glove finger; of being 

 extended, with the disk 3 or more millimeters beyond the 

 mandible and moved through an angle of 90°, so that it is per- 

 pendicular to the stalk, or of assuming any of the innumerable 

 positions between these two. 



The purpose of this paper is to give the anatomical basis for 

 further investigation of the physiological phenomena related to 

 the functions of respiration and capturing and swallowing of 

 prey, and more particularly for understanding these activities 

 during the period of transformation. 



