NECK. 



565 



The stylo-glossus arises, as a round fleshy 

 bundle, from the tip of the styloid process, 

 and from the adjoining part of the stylo-maxil- 

 lary ligament, becomes flattened into divergent 

 parts, as it approaches the side of the tongue 

 at the posterior border of the hyo-glossus, after 

 a short course downward, forward, and inward, 

 and is there inserted. A part is continued for 

 some distance along the hyo-glossus, crossing 

 the direction of its fibres, and interwoven with 

 them ; other fibres seem to bend into the sub- 

 stance of the tongue, near its base and at right 

 angles to its axis. Its surface corresponds to 

 the parotid gland, external carotid artery, in- 

 ternal pterygoid muscle, and mucous mem- 

 brane of the mouth ; deeply, it lies on the in- 

 ternal carotid artery, the superior constrictor 

 of the pharynx, the tonsil and hyo-glossus. 



The genio-hyo-glossus is a large, fan-shaped 

 muscle, radiating from within the symphysis 

 of the jaw to the entire length of the tongue, 

 and constituting, with its fellow, the chief mus- 

 cular bulk of that fleshy organ. It rises by a 

 strong square mass of short tendinous fibres 

 from the upper genial tubercle, and the fleshy 

 fibres, which succeed, immediately and widely 

 diverge; the highest bend upward and some- 

 what forward to the tip of the tongue ; those, 

 which next follow, occupy its entire remaining 

 length, spreading with more or less obliquity 

 into the substance of the organ, through which 

 on a section they may be followed even to the 

 dorsum : some of these may be traced beyond 

 the posterior edge of the hyo-glossus, expand- 

 ing on the side of the pharynx just above the 

 hyoid attachment of the middle constrictor, 

 and constituting the so-called lingual origin of 

 the superior constrictor, (see PHARYNX) ; the 

 remaining fibres complete the semicircular 

 spread of the muscle, by passing downward 

 and backward, to be inserted into the upper 

 border of the body of the os hyoides. This 

 muscle is opposed by its entire mesial surface 

 to its fellow : their tubercles of origin are 

 almost blended on the symphysis, and their 

 fleshy fibres are only to be distinguished by 

 a thin intermediate layer of adipose tissue: 

 their upper edges raise the mucous mem- 

 brane of the mouth on either side of the 

 fraenum ; their lower edges extend to the 

 hyoid bone in perfect parallelism to each other, 

 and to the genio-hyoidei, which cover them ; 

 their outer surfaces, partly covered by the hyo- 

 glossi, form with these on each side the inner 

 wall cf a triangular space (roofed by the mu- 

 cous membrane and floored by the mylo-hyoid 

 muscle) in which lie the terminal branches of 

 the lingual and gustatory nerves, the lingual 

 artery, the sublingual gland, and the excretory 

 duct of the submaxillary. 



Close at the implantation of this muscle in 

 the tongue, between its fibres and those of the 

 hyo-glossus, and crossing the direction of both, 

 is a small bundle of fleshy fibres, which runs 

 longitudinally from base to apex, and, since 

 it has no fixed attachment, may most fitly 

 be considered among the intrinsic muscles of 

 the organ ; it has been named lingualis. (See 

 TONGUE.) 



The genio-hj/oideus is a strong cylindrical 

 muscle intimately associated with the genio- 

 hyo-glossus, and ordinarily co-operating with 

 its posterior fibres. It rises by a square tendon 

 from the inferior genial tubercle, beside its 

 fellow of the opposite side and just below the 

 genio-hyo-glossus. From this origin it directs 

 itself backward and downward, and is inserted 

 into the upper surface of the body of the os 

 hyoides. Its insertion is somewhat broader 

 than its origin : its inner surface corresponds 

 to that of the opposite side; its upper surface 

 is parallel to the genio-hyo-glossus, which it 

 supports ; its under surface rests on the mylo- 

 hyoid, beside its raphe ; its outer surface lias 

 similar relations to that of the genio-hyo- 

 glossus, contributing with it to form the inner 

 wall of the sub-lingual space just described. 



The action of the extrinsic muscles of the 

 tongue is modified and more nicely adapted to 

 the delicate offices of speech by the co-opera- 

 tion of other and intrinsic muscles. These 

 will be described in a future article (see 

 TONGUE). Those already considered operate 

 on the tongue en masse; elevate, advance, 

 depress or retract it, shift its volume to either 

 side, and direct its extremity, by a kind of 

 circumduction, over a wide range of surface. 

 Thus, the stylo-glossus can elevate and retract, 

 the hyo-glossus depress and lateralise ; the 

 anterior fibres of the genio-hyo-glossi, with the 

 linguales, regulate the motions of the tip, while 

 the genio-hyoid and adjunct fibres of the genio- 

 hyo-glossi can cooperate in these movements by 

 shifting the base of support in any direction. 

 As the genio-hyo-glossus is of largest bulk, 

 so is it of most various office in the tongue ; 

 by its posterior fibres it gives an elevation to 

 the os hyoides by which the tongue is protruded 

 from the mouth; or, half antagonizing this 

 action by its middle fibres, it may so forcibly 

 hollow the dorsum of the tongue as to direct 

 its apex within the incisor teeth, and, with aid 

 of the stylo-glossi, enable it to sweep the con- 

 cavity of the palate ; or, by this co-operating 

 with either hyo-glossus and with the opposite 

 lingualis and stylo-glossus, the tongue may be 

 made, as it were, to probe with its eminently 

 tactile extremity the entire length of the alve- 

 olar arches, or by a yet more definite contraction 

 to exert suction on any spot with which its 

 dorsum can have contact. 



The third class includes the sterno-cleido- 

 mastoideus and the platysma myoides. 



The sterno-cleido-mastoideus is a long and 

 powerful muscle, obliquely crossing the side 

 of the neck, from the neighbourhood of the 

 sterno-clavicular joint to the mastoid process 

 of the temporal bone. It is fleshy in almost 

 its whole extent ; flattened at the extremities, 

 but rather prismatic in the intermediate portion; 

 and the anterior edge, which is more particu- 

 larly continuous with the sternal origin of the 

 muscle, and which, in certain positions of the 

 neck, raises the integuments in a well-known 

 diagonal relief, considerably exceeds the thick- 

 ness of the posterior border. The name of 

 the muscle is a summary of its attachments. 

 It arises by two heads, which are usually 



