HYOID APPARATUS OF MAMMALIA. 791 



One is in contact inferiorly with the upper edge of the masseter muscle, 

 and fills up a great part of the space that represents the temporal, zygo- 

 matic, and orbital fossa3, where it partially embraces the globe of the 

 eye : the excretory duct derived from this gland opens into the mouth, 

 behind the superior maxillary bone. The other, which is probably 

 destined to furnish the viscid secretion that coats the worm-like tongue 

 of this animal, is oval and flat, lying in front of the tendon of the mas- 

 seter, behind the angle of the lips, and then running along the edge of 

 the lower lip as far as its middle. Its canal opens externally in a 

 groove at the commissure of the lips ; and a white, thick and tenacious 

 fluid may be pressed out from the cells of which the gland seems to be 

 made up. 



(2293.) In a few species, in addition to the salivary glands met with 

 in Man *, there is a group, apparently a continuation of the molar, 

 which mounts up along the superior maxillary bone, beneath the zygoma, 

 even to behind the globe of the eye. The excretory ducts derived from 

 this group pierce the mucous membrane near the posterior margin of 

 the superior alveolar ridge. Such an arrangement is met with in the 

 Ox, the Sheep, and the Horse. 



(2294.) In the AMPHIBIOUS MAMMALIA the salivary system is very 

 feebly developed ; and in the CETACEA, as might be expected from their 

 habits, no salivary glands whatever are to be detected. 



(2295.) Before considering the mechanism of deglutition in the Mam- 

 malia, we must, in the next place, briefly describe their hyoid appa- 

 ratus ; more especially as this remarkable system of bones, which in 

 the lower Vertebrata was so importantly connected with the respiratory 

 function, is now reduced to an extremely simple condition, and, although 

 it is still intimately connected with the larynx, is more particularly 

 remarkable as forming a centre of attachment for almost all the muscles 

 of the throat. 



(2296.) Perhaps there is no part of the bony framework of the body 

 that exemplifies more strongly than the os hyoides the impossibility of 

 attaining correct physiological views relative to the composition of the 

 skeleton by the mere examination of the human subject. Let the 

 student, for instance, compare for a moment the os hyoides of Man with 

 that of the Fish, or of the Amphibious Reptile, and endeavour, in the 

 simple segment of a circle presented by the one, to find the analogues 

 of the body and complicated arches of the others ; then, doubtless, he 

 will find that, without some intermediate gradations of form, it is not 

 easy to trace the slightest relationship between them. 



(2297.) The human os hyoides consists of a central portion and two 

 cornua ; but these are generally so completely consolidated as to form 

 but one bone, which is connected by the interposition of a broad liga- 

 ment with the upper margin of the thyroid cartilage ; moreover two 

 * Le9ons d'Anat. Comp. iii. p. 210. 



