218 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- 
trinsicmuscles. Initsformitvaries greatly, 
but usually it is slender and is covered with 
retrorse papilla. Its skeleton is also re- 
Fic, 220.—Hyoid peer of duced (fig. ror) and consists of an os en- 
Heloderma, after Cope. _}, first toglossum, bearing in front a pair of ele- 
branchial; c, copula; h, hyoid. : 
ments (paraglosse@) 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. 
Zee : 
Fic. 221.—Two stages in developing tongue and pharyngeal floor of man, after His. 
¢, copula (basihyal element); cs, cervical sinus; ep, epiglottis; g, glottis; h, hyoid arch; m, 
mandibular arch; mth, median anlage of thyreoid; ¢, 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. 
