THE TONGUE. 1579 



ward ; towards the front its fibres are almost longitudinal. The fibres from the lesser 

 horn run on the dorsum beneath the mucous membrane, forming a part of the super- 

 ficial longitudinal system. 



Nerve. The hypoglossal. 



Action. To depress the sides of the tongue, thereby increasing the transverse 

 convexity of the dorsum ; the muscle also retracts the protruded tongue. 



The stylo-glossus (Fig. 1339) arises from the tip of the styloid process and 

 from the beginning of the styio-maxillary ligament. It is a small ribbon-like muscle 

 with an anterior and a posterior surface, but as it descends it twists so as to lie along 

 the outer side of the tongue, which it reaches in the region of the circumvallate 

 papillae. On joining the tongue the fibres divide into an upper and a lower bundle, 

 both of which are chiefly longitudinal, although some fibres blend with the transverse 

 series. It is soon lost in the sheath of longitudinal fibres. 



Nerve. The hypoglossal. 



Action. To retract the tongue and to elevate the sides, thus aiding in pro- 

 ducing transverse concavity of the dorsum. 



The palato-glossus (Fig. 1339) arises from the anterior or buccal aspect of 

 the palate, and descends within the fold forming the anterior pillar of the fauces to 

 the tongue, where it joins the transverse fibres, passing between the two parts of the 

 stylo-glossus. 



Nerve. From the pharyngeal plexus, the motor fibres coming probably from 

 the spinal accessory nerve. 



Action. To elevate the tongue, to depress the soft palate, and, with its fellow 

 by approximating the anterior pillars, to close the fauces. 



FIG. 1340. 



Longitudinal fibres Longitudinal 



fibres 



/;- ^Transverse fibres 



Plica fimbriata Glands Vertical fibres 



Transverse section of tongue of child, near tip. X 3. 



The intrinsic muscles are the lingualis, the transversus, and the perpendicu- 

 laris (Fig. 1340). 



The lingualis, sometimes divided into a superior and an inferior, comprises the 

 greater number of the longitudinal fibres, all, in fact, that do not come from the 

 extrinsic muscles. The thickness of this layer is some 5 mm. 



The transversus furnishes nearly all the transverse fibres, the most important 

 extrinsic contribution being from the palato-glossus. It arises from the septum and 

 runs outward to the mucous membrane ; as it approaches the cortex the fibres break 

 up into bundles, among which pass groups of the fibres of the lingualis. The trans- 

 versus is arranged in a series of horizontal layers, between which pass layers of the 

 vertical set. Thus a horizontal section has the effect of a series of transverse fibres 

 like the bars of a gridiron with the cut ends of the vertical fibres between them and 

 the longitudinal fibres of the lingualis at either side. Near the apex fibres of this 

 system run directly from the mucous membrane of one side to that of the other. 



The perpendicularis is the name given to the few vertical fibres that do not 

 come from the extrinsic muscles. They occur chiefly at the tip and sides, passing 

 from the lower to the upper mucous membrane. 



Nerve. All the intrinsic muscles are supplied by the hypoglossal. 



Action. The tongue is protruded chiefly by the action of the posterior fibres of 

 the genio-glossus, drawing the posterior part of the tongue forward, assisted, perhaps, 

 by the contraction of the transversus. It is withdrawn by its own weight. The 



