MYOLOGY. 53 
side of the median line, and are twenty-one pairs in number, arranged in 
three layers, a superficial, middle, and deep. The superficial consists of 
two pairs, the platysma myoides and sterno-cleido-mastoid. The middle 
may be divided into two orders, the inferior and superior. ‘The inferior are 
three: the sterno-hyoid, sterno-thyroid, and omo-hyoid; the superior are 
nine: digastric, mylo-hyoid, genio-hyoid, three styloid muscles, and the 
hyo-glossus, genio-hyo-glossus, and lingualis muscles. The deep layer con- 
sists of seven pairs: longus colli, rectus capitis, anticus major and minor, 
rectus lateralis, and three scaleni. ‘This arrangement excludes the muscles 
of the palate, pharynx, and larynx. 
The platysma myordes, or latissimus colli, is a thin, pale, cutaneous muscle, 
weak and indistinct in many subjects; it is situated on the fore part and 
side of the neck, extending from the chest and shoulder to the face; it 
arises by many fine fibres from the cellular membrane covering the upper 
part of the deltoid and pectoral muscles. It is inserted, first, into the skin 
and cellular tissue of the chin; second, into the fascia along the sides of the 
lower jaw ; third, into the fascia which covers the parotid, and which adheres 
to the meatus auditorius. Its use is to depress the angle of the lip and the 
lower jaw, as also to compress and support the several muscles, glands, and 
vessels in the region of the neck. | 
The sterno-cleido-mastoideus is situated at the anterior and lateral part of 
the neck : it arises by a strong flat tendon from the upper and anterior part 
of the first bone of the sternum, also from the upper edge of the clavicle, 
and is inserted into the upper part of the mastoid process, and into the 
superior transverse ridge of the occipital bone. The sternal portion can 
rotate the head so as to turn the face towards the opposite side; the clavi- 
cular can bend the head and neck, so as to approximate the ear and shoulder. 
Both portions acting together on each side will move the head downwards 
and forwards. 
The sterno-hyordeus, a long, flat, and thin muscle, arises within the thorax 
from the posterior surface of the first bone of the sternum and sternal end 
of the clavicle, and is inserted into the lower border of the body of the os 
hyoides, internal to the omo-hyoid. Use: to depress the os hyoides, pharynx, 
and larynx. 
The sterno-thyroideus is broader and shorter than the last: it arises from 
the posterior surface of the sternum.and cartilage of the second rib, and is 
inserted into the oblique line on the ala of the thyroid cartilage. Its use is 
to depress the larynx. 
_ The omo-hyoideus is a long and slender muscle, situated. obliquely along 
the inferior, lateral, and fore part of the neck. It arises from the superior 
costa of the scapula behind its semi-lunar notch, and sometimes from the 
acromial end of the clavicle, and is inserted into the lower border of the os 
hyoides. Its use, in conjunction with its fellow on the opposite side, is to 
draw the os hyoides, pharynx, and larynx, downwards and backwards. 
The digastricus, placed at the lateral and anterior part of the neck, thick 
and fleshy at each extremity, round and tendinous in the centre, arises from 
a groove in the temporal bone internal to the mastoid process, and is in- 
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