[74 ATLAS AND TIM BOOK OF HUMAN ANATOMY. 



Fig -Deep layer of the muscles of the neck, seen from the left side. 



The anterior belly of the digastric, the mylohyoid, the sternoi leidomastoid, and the sternal end of the clavicle have 

 been removed. 



Fig. 259. — The deep muscles of the neck, seen from in front. 

 < >n the right Bide the longus 1 apitis has been drawn outward. 



The infrahyoid muscles depress the hyoid hone, the sternothyroid draws down the larynx, and the thyreohyoid 

 approximates the hyoid bone to the larynx. Tiny also a< 1 as accessory muscles of deglutition, and, by its attachment to 

 the sheath of the gnat vessels, the omohyoid facilitates the return of blood through the internal jugular vein. 



The Suprahyoid Muscles. 



The suprahyoid muscles (Figs. 255 to 258) lie between the hyoid bone and the mandible. 

 They arc the digastricus, the stylohyoideus, the mylohyoideus, and the geniohyoideus. 



The digastricus (biventer mandibuke) (Figs. 255, 256, and 258) is a typical two-bellied 

 muscle with a distinct cylindrical intermediate tendon which is attached to the hyoid bone. The 

 two bellies form an obtuse angle, open above, in which is situated the submaxillary salivary gland. 

 The anterior belly is a fairly thick muscle which passes from the intermediate tendon, frequently 

 receiving a few tendinous fibers directly from the hyoid bone, to the digastric fossa of the mandible, 

 where it is inserted by a short tendon. The posterior belly is longer but somewhat weaker than 

 the anterior one. It arises from the mastoid notch of the temporal bone and passes with the 

 stylohyoideus to the hyoid region, where it becomes continuous with the intermediate tendon. 



The anterior belly of the digastric lies in the submental and mental regions, between the skin 

 and the mylohyoid; the posterior belly is completely concealed at its origin by the sternocleido- 

 mastoid, and further anteriorly it separates the submaxillary region from the carotid fossa. 



When the hyoid Knne is fixed, the anterior belly depresses the lower jaw and opens the mouth; the posterior belly 

 draws tne hyoid bone ba< kward and upward and, together with the stylohyoid and the infrahyoid muscles, fixes the hyoid 

 bone. The posterior belly is supplied by the facial nerve, the anterior belly by the mylohyoid nerve from the third divi- 

 of the trigeminus. 



The stylohyoideus (Figs. 255, 256, and 258) arises by a tendon from the styloid process of 

 the temporal bone and runs to the hyoid bone as a flat rounded muscle above and almost parallel 

 to the posterior belly of the digastric. Before its insertion into the bone it almost always divides 

 into two slips, between which the intermediate tendon of the digastric passes. These slips have 

 muscular attachments to the base of the greater cornu and to the posterior extremity of the body 

 of the hyoid bon< . 



- 



The action of the muscle is similar to that of the posterior belly <>f the digastric and it is also supplied by the 

 fai ial nerve. 



between tin- infrahyoid muscles and the anterior border of the Sternocleidomastoid then- remains a deep 

 bounded above by the posterior belly of the digastricus; this i> the carotid fossa, ami it contains the great vi- 

 and nerve of the neck (the (.mmion tarotid artery, the internal jugular vein, and the vagus nerve). The lateral wall 

 of the pharynx fornix its floor. 



The mylohyoideus (Figs. 256 to ~m\ 2(>s is a peculiar broad, flat muscle which is 



situated in the submental and submaxillary regions and is partly covered by the anterior belly of 



