388 THE MUSCULAR SYSTEM. 
a. Elevation and Depression. b. Protraction and Retraction. 
Digastric Thyro-hyoid | Genio-hyoid | Stylo-hyoid 
Stylo-hyoid 
Mylo-hyoid 
Sterno-hyoid 
Omo-hyoid 
| Genio-hyo-glossus 
| 
| Middle constrictor 
Genio-hyoid Sterno-thyroid 
Genio-hyo-glossus 
Hyo-glossus 
Muscles closing the 
mouth 
(2) Movements of the Thyroid Cartilage——The thyroid cartilage is raised 
during speech and deglutition. 
Elevation. 
Thyro-hyoid 
Stylo-pharyngeus 
Palato-pharyngeus 
Elevators of hyoid bone 
Muscles closing mouth 
(3) Movements of the Tongue.—The chief movements of the tongue in speech and de- 
glutition are elevation and depression, protrusion and retraction, and lateral movements 
a. Elevation 
Palato-glossus 
Muscles elevating hyoid bone 
| 
| 
Stylo-glossus (base) 
Muscles closing nouth 
b. Protrusion 
Genio-hyo-glossus (posterior fibres) 
Depression. 
| Sterno-thyroid 
Crico-thyroid 
| Depressors of hyoid bone 
and Depression. 
Genio-hyo-glossus 
Hyo-glossus 
| Chondro-glossus 
Muscles depressing the hyoid bone 
and Retraction. 
Genio-hyo-glossus (anterior fibres) 
and lowered 
Stylo-glossus 
c. Lateral Movements.—The muscles of one side only. 
! —Es —— = es es 
(4) Movements of the Head.—The sterno-mastoid muscles, acting together, flex the head on 
the spinal column, assisted by the supra-hyoid and infra-hyoid muscles. The sterno-mastoid muscle 
of one side, acting alone, bends the head to the same side, and simultaneously rotates it to the 
opposite side, as seen in torticollis (wryneck). 
(5) Movements of the Shoulder Girdle—The omo-hyoid and sterno-mastoid muscles have 
already been included among the elevators of the shoulder girdle. 
(6) Respiration.—The muscles on the front of the neck are auxiliary muscles in extraordinary 
or difficult inspiration. The masseter and temporal muscles fix the lower jaw ; the hyoid bone is 
raised and fixed by the supra-hyoid muscles ; and the sternum is raised by the sterno-mastoid and 
infra-hyoid muscles. 
THE MUSCLES OF THE PHARYNX. 
The muscular envelope of the pharynx is composed of two strata. The external 
layer consists of the three constrictor muscles; the internal layer consists of the 
longitudinal fibres of the stylo-pharyngeus and palato-pharyngeus muscles. 
The superior constrictor muscle is triangular or fan-shaped. It arises 
successively from the lower half of the posterior border of the internal pterygoid 
plate, from the pterygo-mandibular ligament, from the mylo-hyoid ridge of the 
lower jaw, and from the mucous membrane of the floor of the mouth (glosso- 
pharyngeus). The muscular fibres radiate backwards, and are inserted for the 
most part into a median raphe extending down the back wall of the pharynx in 
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