THE TONGUE. 



1577 



the base of the palato-glossal fold. Anteriorly towards the dorsum the serous glands 

 remain isolated ; posteriorly they come into contact with the mucous glands, so that 

 alveoli of both varieties may be included within a single microscopical field ( Fig. 1287 ). 



The posterior third of the dorsum, from the circumvallate papillae backward, 

 possesses a rich, almost continuous layer of mucous glands, 5 mm. or more in thick- 

 ness, which lie beneath the mucous membrane and mingle with the lymphoid tissue. 

 Since the alveoli lie among the muscles at some depth, the excretory ducts often 

 attain a length of from 10-15 mm., and open on the free surface in close association 

 with the lymph-follicles. 



The anterior mucous glands (Fig. 1352) are disposed principally as two elon- 

 gated groups, glandules linguales anteriores, or glands of Nuhn, or of Blandin 

 (from 15-20 mm. in length, 7-9 mm. in width, and somewhat less in thickness), 

 which lie on either side of the mid-line, near the tip of the tongue, among the mus- 

 cular bundles. They meet in front, but diverge behind, where they may be con- 



FIG. 1338. 



Lymph-node 



Glands 



Interlacing fibrous and 

 muscular bundles 



Glands. 



Section from posterior third of child's tongue, showing lymph-nodes constituting a part of lingual tonsil. X 30. 



tinued backward by additional collections of mucous glands along the edges of the 

 tongue. The ducts five or six in number open on the folds occupying the under 

 surface of the tongue near the frenulum. 



Muscles of the Tongue. These include two groups, the extrinsic and the 

 intrinsic muscles. The former pass from the skull or hyoid bone to the tongue ; the 

 latter comprise the particular muscles both arising and ending within the organ. Their 

 general arrangement is as follows. Under the mucous membrane is a dense sheath 

 of longitudinal fibres, surrounding the others completely near the apex, and farther 

 back wanting at the middle of the under surface where the fibres of the genio-glossi 

 and hyo-glossi enter the organ. This outer layer is the cortex. The inner part is 

 divided into two by a vertical median septum of areolar tissue, which is quite dense 

 in its upper part. It is sickle-shaped, with the point in front and not reaching the 

 apex. The inner portion, or medulla, is composed of transverse muscle-fibres inter- 

 posed between layers of those called vertical, which in fact present many degrees of 

 obliquity. 



The extrinsic muscles are fatgenio-glossus, the kyo-glossus, the stylo-glossus, 

 and the palalo-glossus, to which may be added, from its position, the genio-hyoid. 

 All of these are in pairs and symmetrical. 



