24 ANATOMY OF VERTEBRATES. 



df which the base of the tongue is situated, and here they con- 

 verge .and blend with corresponding flattened fasciculi, sent off 

 ffom the lower part of the genioglossi, as these pass backward to 

 the base of the tongue. The main continuation of the sterno- 

 glossus, i s forms a rounded slender muscle, which raises the buccal 

 membrane so as to form the back part of the fraenum lingua?, 

 penetrates the back part of the base of the tongue, and constitutes 

 a great proportion of its substance. 



The genioghssust ib. m, n, o, has a complex origin, by a middle 

 portion, from the short symphysis mandibular, and by a flattened 

 penniform series of fibres* form the lower border of the mandi- 

 bular rami for the extent of four inches behind the symphysis. 

 The symphysial origin is round and slender, and belongs more 

 directly to the proper tongue-muscle : the ramal origins seem to be 

 the more special fixed point of the subgular fasciculi. The fibres 

 of the latter origin pass obliquely backward and inward, con- 

 verging to a middle raphe* to which the symphysial origin closely 

 adheres. The two origins of the muscle are blended into one 

 for about three inches beyond the point of attachment, in which 

 extent the muscle forms a moderately thick depressed mass along 

 the middle of the under part of the mouth. It then begins to 

 expand, and to detach from its under surface those subgular 

 fasciculi, which diverge and unite with the corresponding dis- 

 memberments of the sternoglossi, The main part of the genio- 

 glossus enters, as a single muscle, the fore part of the base of the 

 tongue, carrying into the floor of the mouth a fold of buccal 

 membrane forming the fore part of the fraenum linguae. 



Beneath the insertions of the geniohyoid ei, a pair of more slender 

 muscles, epihyoglossi, come off' from the median ends of the 

 epihyals. These muscles, after a brief course, expand into a thin 

 layer, resolve themselves into separate fasciculi, and combine an 

 inch in advance of their origin to form a layer about eight lines 

 in breadth below the middle line of the post-lingual part of the 

 mouth, which layer slightly diminishes in size as it approaches 

 the commissure of the Sternoglossi, and, with them, penetrates 

 the back part of the fraenum linguae. 



§ 196. Muscles of Cetacea. — In the Cetacea the muscles of 

 the trunk are chiefly developed : those of the limbs are restricted 

 to the pectoral pair. Swimming is the principal mode of progres- 

 sion in the muticate orders of Gyrencephala : but the phytophagous 

 Siren la have the power, in order to feed upon marine or littoral 

 plants, of crawling at the bottom of the sea and shuffling along 



