FUNCTIONS OF MUSCLES 501 



mate. Owing to the influence of gravity, the relations of other muscles to the skeleton, and 

 similar factors, a given muscle may perform functions which would not be deduced from a simple 

 study of the relations of the muscle to the skeleton. Thus the iliacus serves to flex not only the 

 hip, but also the knee, and the hamstring muscles may flex the hip while flexing the knee. The 

 functions ascribed to various muscles in the following tables, although an attempt has been 

 made to base them upon the more recent work on the action of the muscles, must be taken to 

 be merely approximately correct. So far as possible the muscles are given in order of their 

 power in efi'ecting the various movements. In this we have utilized chiefly the work of R. Fick: 

 "Anatomie und Mechanik der Gelenke unter Berticksichtigung der bewegenden Muskeln" 

 in von Bardeleben's Handbuch der Anatomie des Menschen. 



tin this table have been included not only the voluntary muscles described in the preceding 

 section, but also several described in other parts of the book. 



1. Facial muscles. 



These serve essentially to contract the various visceral orifices of the head or to retract 

 the tissue surrounding them. 

 Ear. 



Retractors: auricularis anterior, superior, and posterior. 

 Orbit. 



(a) Retractor: Epicranius (occipito-frontalis). The levator palpebrae 



superioris, innervated by the third cranial nerve, serves to 

 raise the upper lid of the eye. 



(b) Contractors: orbicularis oculi, corrugator, and procerus. 

 Nasal orifice. 



(a) Dilators: angular head of the quadratus labii superioris, transverse 



portion of the nasalis, and the dilatores naris. 

 (6) Contractors: pars alaris of the nasalis and the depressor septi nasi. 

 Oral orifice. 



(a) Retractors: 



Upward: zygomaticus, quadratus labii superioris, caninus. 

 Lateralward: zygomaticus, risorius, platysma, triangularis, bucci- 

 nator. 

 Downward: triangularis, quadratus labii inferioris, platysma. 

 (6) Contractors: orbicularis oris, compressor labii, incisivus labii inferioris 

 and superioris. 



(c) Protractors of the lips : incisivus labii inferioris and superioris, mentalis. 



2. Muscles acting on the eyeball (see Section on Eye). 



To adduct the pupil: rectus medialis. 

 To abduct the pupil: rectus lateralis. 

 To direct the pupil upward: rectus superior, in association with the obliquus 



inferior. 

 To direct the pupil downward: rectus inferior, in association with the obUquus 



superior. 



3. Muscles acting on the lower jaw. 



(a) To raise it: masseter, temporal, internal pterygoid. 



(6) To lower it: external pterygoid, digastric, mylo-hyoid, genio-hyoid, and the 



infrahyoid muscles. The weight of the jaw also plays a part in 



this movement. 



(c) To protract it: external pterygoid, internal pterygoid, masseter and the ante- 



rior part of the temporal. 



(d) To retract it: the inferior dorsal portion of the temporal and the digastric. 



(e) To produce lateral movements: the external pterygoid acting on one side 



rotates the chin and carries the jaw toward the opposite side. 

 The rotation may be aided by the digastric of the opposite 

 side. The masseter draws it slightly toward the side on which 

 the muscle lies. This action of the masseter is counterbalanced 

 by the internal pterygoid (Riegner). 



4. Muscles ac 



5. Muscles ac 



ing on the hyoid bone. 



c) To elevate it: digastric, stylo-hyoid, stylo-glossus, mylo-hyoid, genio-hyoid, 



genio-glossus, hyo-glossus, and the middle constrictor of the 



pharynx. 



b) To depress it: thyi-eo-hyoid, sterno-hyoid, omohyoid, sterno-thyreoid. 



c) To protract it: genio-glossus (inferior portion), genio-hyoid, anterior belly of 



digastric, and the mylo-hyoid. 



d) To retract it: posterior beUy of digastric, stylo-hyoid, and the middle con- 



strictor of the pharynx, 

 ing on the larynx (see Section IX). 



a) To elevate it: thyreo-hyoid, stylo-pharyngeus, pharyngo-palatinus, the in- 

 ferior constrictor of the pharynx, and the elevators of the hyoid 

 bone. 



b) To depress it: sterno-thyreoid, sterno-hyoid, and omo-hyoid. 



c) To approximate the vocal cords: crico-arytenoideus laterahs; vocalis; 

 thjTeo-arytenoideus, arytenoideus transversus. 



d) To make the vocal cord tense: crico-thyreoideus. 



e) To widen the rima glottidis: crico-arytenoideus posterior. 



/) To shorten and thicken the vocal cords: thyreo-arytenoideus (externus), 

 vocalis. 



