404 THE DIGESTIVE APPARATUS IN MAMMALIA. 



comprise a superior and inferior, a transverse and a vertical linguaUs muscle, 

 found on the inferior aspect of the free portion of the organ. An attentive 

 examination, however, reveals that the fibres proper to this submucous layer are 

 continuous with those which, coming from a point situated beyond the tongue, 

 form the muscles named, in consequence, extrinsic, and that they are only the 

 prolongations of these. This division of the tongue into two orders of muscular 

 fasciculi does not, for this reason, possess the importance generally accorded 

 to it. 



Extrinsic muscles. — If the muscular fibres of the tongue appear to be one 

 mass in the superior layer just referred to, it is not so when they are followed 

 beyond this layer ; on the contrary, we see them separate from one another, and 

 even admit between them — at least in the fixed portion — a certain amount of 

 adipose tissue, which is particularly abundant towards the base, where it forms 

 a mass called the fattij nucleus of Baur ; then they collect into fasciculi, or per- 

 fectly distinct muscles. 



In Solipeds, these muscles number five pairs : 1. The stylo-glossus. 2. The 

 great hyo- or hasio-glossus. 3. The genio-glossus. 4. The small hyo-glossus 

 (the superior lingual of some authorities). 5. The pharyngo-glossus. 



Stylo-glossus (Hyo-glossus Longus) (Fig. 220, 1). 



Synonym. — Kerato-glossus externus — Leyh. The stylo-glossus of Man. 



This is a very long riband-shaped band, formed of bright-red parallel fibres, 

 and extending from the styloid bone, or great cornu of the os hyoides, to each 

 side of the free extremity of the tongue. 



It arises from the external surface of the large cornu, near its inferior 

 extremity, by a very thin aponeurosis ; it terminates near the tip of the tongue, 

 in expanding over the inferior surface and borders of the organ, and mixes its 

 fibres with those of the opposite muscle. 



In the fixed portion of the tongue, this muscle is related : outwardly, to the 

 mylo-hyoideus, sublingual gland, hngual nerve, and the Whartonian duct ; m- 

 wardly, to the genio-glossus and great hyo-glossus muscles. The whole of its 

 free portion is covered by the buccal membrane. 



In contracting, this muscle pulls the tongue towards the back of the mouth ; 

 it inclines it to one side when acting independently of its fellow on the opposite 

 side. 



Great Hyo-glossus, Basio-glossus (Hyo-glossus Brevis) (Fig. 220, 2). 



Synonym. — Hyo-glossus — Leyh. 



A wide muscle, flattened on both sides, thicker than the preceding, and com- 

 posed of fibres passmg obliquely forward and upward, the longest of which are 

 anterior. 



Its origin occupies the whole side of the body of the os hyoides, from the 

 extremity of the cornu to that of the spur process. Its fibres, after becoming 

 detached from this point of insertion, are insinuated beneath the preceding 

 muscle, spread out under the mucous membrane covering the lateral aspect of 

 the tongue, and for the most part are reflected inwards, nearly to the superior 

 face, to constitute the transverse fibres of the organ. 



