THE MUSCULAR SYSTEM 



27: 



masseter, which raises the mandible; the temporalis, which raises the 

 mandible and draws it back. The chief function of the pterygoids, 

 internal and external, is in moving the jaw from side to side, as in chewing. 

 The digastric lowers the jaw. 



Some of the tongue muscles are intrinsic but most are extrinsic. The 

 intrinsic lingualis forms an interwoven complex extending longitudinally, 

 vertically, and transversely. Of the extrinsic group, the hyoglossus and 

 styloglossus retract the tongue, while the genioglossus, which forms most 



SPLENIUS- 



SEMISPINALIS 

 CAPITIS. 



LEVATOR 

 SCAPULAE- 



SCALENUS 



MEDIUS 



SCALENUS 

 ANTERIOR- 



LONGUS 

 CAPITIS 



ESOPHAGUS 

 ARYTENOIDEUS 

 TRANSVERSU 



THYREOARYTENOID 



TRANSVERSUS 

 r-SPINALIS. 



LONGISSIMUS 

 CAPITIS. 



LONGISSIMUS 

 ERVICIS. 



CONSTRICTOR 



PHARYNGIS 



INFERIOR. 



■STERNOCLEIDO- 

 MASTOID. 



PLATYSMA- 

 STERNOHYOID 



MOHYOID. 



STERNOTHYROID- 



■THVREOHYOID- 



ICAVITY OF LARYNX . 



Fig. 229. — Human neck muscles in cross section. Muscles stippled and skeletal 

 elements cross-hatched. (Redrawn after Morris modified.) 



of, the body of the tongue, both extends and retracts it, depending upon 

 which part of the muscle contracts. 



Another group of muscles lies in the floor of the throat between the 

 mandibles and thehyoid bone, among them the anterior belly of the digas- 

 tric, the geniohyoid, and the mylohyoid. The stylohyoid and the posterior 

 belly of the digastric extend from the hyoid to the styloid process. Food 

 is forced into the esophagus by a group of constrictor muscles of the 

 pharynx. 



Muscles of the Neck. In addition to the cutaneous platysma, the 

 neck contains sixteen paired muscles. Underneath the platysma on the 

 side of the neck, the conspicuous stemocleido-mastoid bends and rotates 

 the head. The trapezius, strictly a muscle of the shoulder, extends well 

 up on the back of the neck. Another shoulder muscle, the levator 

 scapulae, draws the shoulder blade towards the head. (Fig. 229.) 



