THE MUSCLES OF THE TONGUE. 499 



than in the case of softer food; this is probably, in part at least, due 

 to the more vigorous action of the muscles of mastication, exciting a 

 general determination of vascular and nervous energy to the parts. 

 It was found by Bernard, in experiments made by opening the oesopha- 

 gus of a horse, that the mass of food swallowed, was usually mixed 

 with about ten times its weight of saliva; when the Whartonian ducts 

 were tied, mastication was performed much more slowly, and the food 

 mass, taken from the oesophagus, was drier, though covered with 

 mucus, and weighed only three and a half times its original weight. 



Certain movements, which co-operate in mastication, are performed, 

 within the dental arches, by the tongue, and on the outer side of these 

 arches, by the buccinators, or cheek muscles, which compress the cheeks. 

 These movements serve to place, and hold, the food between the teeth, 

 to turn it, so that fresh portions may be subjected to the pressure of 

 the teeth, and, finally, when it is fully masticated, to push or withdraw 

 it from between the teeth, so that it may be swallowed. The tongue 

 also aids in crushing soft masses of food, and forming them into suit- 

 able boluses to pass into the pharynx and gullet. 



The tongue is a muscular organ, composed of two symmetrical halves, 

 separated from each other by a median fibrous septum, and covered by 

 mucous membrane and a submucous fibrous stratum. The muscles of 

 this organ are extrinsic and intrinsic. The former pass into the tongue 

 at its base and under surface, and connect it with neighboring parts ; 

 they are four in number in each half of the tongue, viz., the hyo-glos- 

 sus, the genio-Jiyo-glossus, the stylo-glossus, and the palato-glossus, so 

 named from their respective bony attachments. A few fibres of the 

 superior constrictor muscle of the pharynx are also connected with the 

 side of the tongue. The intrinsic, or proper muscles of the tongue, 

 are the superior longitudinal, the inferior longitudinal or lingualis, and 

 the transverse. 



The hyo-glossus is a thin quadrilateral muscle, which, arising from 

 the hyoid bone, passes upwards to the side of the tongue, to be inserted 

 between the stylo-glossus and the lingualis. Beneath the hyo-glossus 

 is a flat triangular muscle, the genio-hyo-glossus, the apex of which 

 arises from the inner surface of the anterior portion of the lower jaw, 

 its base being inserted into the hyoid bone, a small portion of the pha- 

 rynx, and the entire length of the under surface of the tongue. The 

 stylo-glossus arises from the styloid process of the temporal bone, and 

 divides into two portions on the side of the tongue, one longitudinal, 

 blending with the lingualis, the other oblique, decussating with the 

 hyo-glossus. The palato-glossus, which, as previously mentioned, 

 forms, on each side, the anterior pillar of the soft palate, passes from 

 the soft palate to the side and upper surface of the tongue, where it 

 joins the fibres of the stylo-glossus. 



Of the intrinsic muscles, the superior longitudinal muscle occupies 

 the upper surface of the tongue, close beneath the mucous membrane, 

 extending from its apex to the hyoid bone ; some of the fibres are 

 longitudinal, others oblique ; many of them are branched or undergo 

 subdivision, and are connected, at intervals, with the submucous and 

 glandular structures. The inferior longitudinal, or lingualis, muscle 



