48o 



HUMAN ANATOMY. 



{a) THE HYOIDEAN MUSCLES. 



I. Stylo-hyoideus. 2. Digastricus (Posterior Belly). 3. Stapedius. 



I. Stylo-Hyoideus (Figs. 497, 502). 



Attachments. — The stylo-hyoid forms a slender spindle-shaped muscle which 

 arises from the upper portion of the styloid process and passes obliquely downward 

 and forward to be inserted into the base of the greater cornu of the hyoid bone, 

 usually dividing before its insertion into two slips, between which the intermediate 

 tendon of the digastric passes. 



Nerve-Supply. — By a branch from the digastric branch of the facial nerve. 



Action. — To raise and draw backward the hyoid bone. 



Relations. — Above the stylo-hyoid descends along the inner border of the 

 posterior belly of the digastric, passing in front of that muscle below. Internal to 

 it is the stylo-pharyngeus, and below the hyo-glossus and the glosso-pharyngeal and 

 hypoglossal nerves, passing forward between it and the stylo-pharyngeus. 



2. Digastricus (Posterior Belly). See page 478. 

 3. Stapedius (Fig. 1254). 



Attachments. — The stapedius arises from the walls of the cavity contained 

 within the pyramidal eminence, and its tendon, entering the tympanic cavity through 

 the aperture at the apex of the eminence, is inse^^ted into the neck of the stapes. 



Nerve-Supply. — By a small branch arising from the facial nerve during its 

 course through the lower part of the facial (Fallopian) canal. 



Action. — By its contraction it draws the head of the stapes towards the pos- 

 terior wall of the tympanic cavity, depressing the posterior part of the foot-plate of 

 the bone while it raises the anterior part, thus tensing the membrane which closes 

 the fenestra ovalis. 



Variations of the Hyoidean Muscles. — A close relationship exists between the stylo-hyoid 

 and the posterior belly of the digastric, the one or the other occasionally failing to separate 

 from the common mass from which they are derived. A bundle of muscle-fibres sometimes 

 passes from the tip of the styloid process to the angle of the mandible, forming what may be 

 termed the stylo-rnatidibularis, and recalling hy its insertion the condition presented in certain 

 cases by the posterior belly of the digastric ( page 479 ) . 



A duplication of the stylo-hyoid has also been observed, the second slip, which has been 

 termed the stylo-hyoideus profundus, varying considerably in its insertion, sometimes accompa- 

 nying the stylo-hyoid proper and sometimes inserting into the lesser cornu of the hyoid, and in 

 some cases replacing the stylo-hyoid ligament. 



The division of the stylo-hyoid near its insertion for the passage of the intermediate tendon 

 of the digastric does not always occur, the insertion being by a single head which may pass 

 either to the outer or the inner side of the tendon. 



{b) THE PLATYSMA MUSCLES. 



et 



The comparative and embryological study of the platysma muscles have shown 

 their origin from the musculature of the second or hyoid arch and their extension 



