556 DB. J. MUEIE ON THE ANATOMY OP THE SBA-LION. 



mingle with each other in the middle line of the inframandibular region, rather forming 

 a continuous whole and tolerably thick layer than thinning into a median longitudinal 

 raphe. Anteriorly the fibres curve forwards ; and centrally, about the middle, they have 

 a transverse direction, while posteriorly they bend inwards and backwards. The latter 

 are not inserted upon the basihyal of the os hyoides, but rather superficial to it, being 

 fixed by strong tendinous fascia to the fibres of the sterno-hyoid, omo-hyoid, and hyo- 

 glossus muscles. Thus, as regards their action, the fibres of the mylo-hyoid are con- 

 tinuous wdth those derived from the sternum, and therefore must act inversely as a long 

 lever, according as they act from the fixed point at either end. It follows also that 

 they have an increased power of compressing the tongue and fauces during deglutition. 



Together the genio-hyoidei form a thick tongue-shaped muscular mass arising 

 anteriorly from the concavity of the mandibular symphysis, posteriorly spreading out 

 and thinning as they are inserted in a continuous arched manner into the whole front 

 of the basihyals and root of thyrohyals. Although divisible into two lateral equal- 

 sized muscles, the fibres of the genio-hyoids are closely bound together, and, like the 

 mylo-hyoidei, present scarcely any raphe. The fibres of each genio-hyoid at its 

 insertion run outside into those of the middle constrictor of the pharynx, and likewise, 

 with only a very indefinite fibrous division, join those of the sterno- and omo-hyoid. 

 The genio-hyoids, from their great strength, must act very powerfully in drawing 

 forwards the hyoidean apparatus, and also greatly assist the closure and grasping move- 

 ment of the upper pharyngeal constrictor. Their outer insertions compress or bring 

 together the thyrohyals. It may further be remarked that, when examined deeply, 

 each genio-hyoid is seen to be composed of what might be considered two parts. The 

 middle appears as a long strong muscle with straight fibres inserted into the basihyal 

 and sterno-hyoid muscle. Outside this, behind and superficially, a thin layer diverges to 

 be partially inserted into the root of the thyrohyal and to intermingle with the omo- 

 hyoid and middle constrictor. 



The massive genio-hyoglossi may be considered an azygos plane of muscular fibres 

 originating at the symphysial cleft, and, therefrom assuming a fan-shape, are directed 

 upwards and forwards to the tip of the tongue. Medianly they become vertical, and 

 posteriorly gain the horizontal line ; inferiorly the horizontal fibres of the genio-hyo- 

 glossi are flattened or slightly scooped out to receive the thick genio-hyoid muscles. 



The fibres of the anterior three fourths of each muscle do not ascend to the substance 

 of the tongue. The remaining fibres are mainly inserted upon, and partly go to the 

 inferior wall or basis of the pharynx. Those that go backwards are inserted into the 

 upper surface of the basihyal and side of the ceratohyal. 



Hyoglossus. — This muscle is large and tolerably thick, broad behind and narrow 

 wedge-shaped in front, also convex below and concave or deeply scooped out above, so 

 as to fit into the prominent ceratohyals. Its origin is from the ceratohyal, thyrohyal, 

 and posterior root of the basihyal ; its outer corner of origin from the thyrohyal is 



