2l8 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



tip; in the lizards its shape varies greatly, the differences being used in 

 classifying these animals. In the reptiles (fig. 220) with retractile 



tongue the hyoid apparatus extends into 

 the tongue, its unpaired anterior portion 

 being called the os entoglossum (copula 

 or basihyal), while the two cornua (usually, 

 hyoid and first branchial) afford attachment 

 for the retractor muscles. In addition to 

 the usual lingual nerve (glossopharyngeal) 

 the tongue also receives a lingual twig from 

 the mandibular branch of the fifth nerve. 



In birds the tongue has lost the lateral 

 parts of the reptilian tongue and with this 

 the trigeminal branch. It contains no in- 

 trinsic muscles. In its form it varies greatly, 

 but usually it is slender and is covered with 

 retrorse papillae. Its skeleton is also re- 



duced ' MI and consists of an os e - 



FIG. 220 . Hyoid apparatus of 



Heloderma, after Cope, b, first toglossum, bearing in front a pair of ele- 



branchial; c. copula; h. hyoid. , , 



ments (paraglossae) and on the sides a 



pair of cornua (first branchials) and in the median line behind, a 

 urohyal portion. This skeleton has a marked development in the 

 woodpeckers, where the cornua curve around the base of the skull 



FIG. 221. -Two stages in developing tongue and pharyngeal floor of man, after His. 

 c, copula (basihyal element); cs, cervical sinus; ep, epiglottis; g, glottis; h, hyoid arch; m, 

 mandibular arch; mth, median anlage of thyreoid; t, tuberculum impar; tg, tongue. 



and over its dorsal side to the neighborhood of the nostril, a condi- 

 tion correlated with the use of the tongue in these animals. 



