DIGESTIVE ORGANS. 



219 



In the whales the tongue has little power of motion, but elsewhere 

 in the mammals it is very mobile, reaching the extreme in the ant-eaters. 

 This mobility is largely due to the extensive intrinsic musculature. 

 The tongue is developed from the tuberculum impar, which furnishes 

 the larger anterior part (fig. 221), the rest arising from the fleshy ridges 

 above the hyoid arch. In the adult the line between these parts is largely 

 obliterated, but it lies near the line of circumvallate papillae (p. 189) 

 and the foramen caecum, a blind tube connected with the development 

 of the thyreoid gland. Arising in this s 



way from the tubercle and the lateral supra- 

 hyoid parts, the tongue of the amphibia is 



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it 



I 



FIG. 222. FIG. 223. 



FIG. 222. Ventral and side views of tongue of Stenops gracilis, after Weber. I, 

 lateral margin of sublingua; m, plica mediana. 



FIG. 223. Section through lyssa of late dog embryo, after Nussbaum. c, cartilage of 

 lyssa, cl, capsule of lyssa; m, muscles of tongue; ml, longitudinal and transverse muscles 

 of lyssa; s, septum of tongue. 



unrepresented in that of most mammals, unless it be in the sublingua, 

 a fleshy fold developed beneath the functional tongue in the marsupials 

 and lemurs (fig. 222). Traces of this are to be found in other mam- 

 mals, even in man, as folds (plicae fimbriatae) beneath the tongue. 

 In some cases (Stenops) this sublingua is supported by a cartilage 

 which is regarded as an entoglossal part. Others think that the 

 tongue of the lower vertebrates is represented in the mammalian 

 tongue and regard the lyssa as the os entoglossum. The lyssa is 

 a vermiform structure of cartilage, muscle and connective tissue (fig. 

 223) lying ventral to the septum of the tongue. 



The tongue varies considerably in shape in the different mammalian 

 orders, but the differences are of little morphological importance. 



