386 THE MUSCULAR SYSTEM. 
boundary of the submaxillary space. The posterior belly is concealed at its origin 
by the mastoid process and the muscles attached to it. It crosses the carotid 
vessels and the hypoglossal nerve in the anterior triangle. The anterior belly 
covers the mylo-hyoid muscle. ; 
The stylo-hyoid muscle arises from the styloid process of the temporal bone, 
and is inserted into the body of the hyoid bone by two slips which enclose the 
tendon of the digastric muscle. It is directed downwards and forwards alongside 
the posterior belly of the digastric, and crosses the anterior triangle in front of the 
carotid vessels. 
The mylo-hyoid muscle arises from the lower three-fourths of the mylo-hyoid 
ridge of the lower jaw. It is directed downwards and inwards, to be inserted into 
the upper border of the body of the hyoid bone, and more anteriorly (along with 
the opposite muscle) into a median raphe extending from the hyoid bone nearly to 
the chin. The muscle forms a diaphragm in the floor of the mouth, and has in 
contact with its external surface the digastric muscle and the submaxillary gland. 
Its internal surface is partially covered ‘by the mucous membrane of the floor of the 
mouth, and is separated from the hyoglossus and genio-hyoglossus muscles by the 
deep part of the submaxillary gland, “the sublingual gland, Wharton’s duct, and 
the lingual and hypoglossal nerves. 
The genio-hyoid muscle arises from the lower of the two genial tubercles on 
the back of the symphysis of the lower jaw. It is directed downwards and _ back- 
wards, to be inserted into the body of the hyoid bone. The muscle is concealed by 
the digastric and mylo-hyoid muscles. It les along the lower border of the genio- 
hyoglossus. The muscles of opposite sides are often fused together. 
THE MUSCLES OF THE TONGUE. 
The muscular substance of the tongue consists of two symmetrical series of 
muscles placed on either side of a membranous raphe in the middle line, and 
composed of (1) extrinsic muscles arising from the soft palate, styloid process, hyoid 
bone and lower jaw, and (2) intrinsic muscles, proper to the tongue itself. Hach 
set consists of four series of muscles. 
The extrinsic muscles are four in number: (1) genio-hyo-glossus, (2) hyo- 
glossus, (3) stylo-glossus, and (4) palato-glossus. 
The genio-hyo-glossus muscle (Fig. 283) is an extrinsic muscle of the tongue 
as well as a supra-hyoid muscle. It is a fan-shaped muscle arising by its apex 
from the upper of the two genial tubercles behind the symphysis of the lower jaw. 
From this origin the muscular fibres diverge; the lowest fibres are directed down- 
wards and backwards, to be inserted into the body of the hyoid bone; the highest 
fibres curve forwards, to be attached to the tip of the tongue ; the intermediate fibres 
are attached to the substance of the tongue between the base and tip. ‘The muscles 
of opposite sides are separated by the median raphe of the tongue. On the outer 
side of each are placed the hyo-glossus and mylo-hyoid muscles. Between the hyo- 
glossus and genio-hyo-glossus are found the stylo-hyoid ligament, the lingual artery, 
and the glosso-phary ngeal nerve. 
The iyo: glossus raeele is also an extrinsic muscle of the tongue as well as a 
supra-hyoid muscle. It arises from the hyoid bone (body and oreat cornu), and is 
directed upwards and forwards, to be inserted into the side of. the tongue, inter- 
lacing with the stylo-glossus. The muscle is quadrilateral, and hes between the 
genio- -hyo-g glossus and mylo- hyoid muscles, separated from the latter by the mucous 
membrane of the floor of the mouth, the sublingual and part of the submaxillary 
glands, the lingual and hypoglossal nerves, and ‘Wharton’s duct. 
The chondro-glossus is a small separated slip of the hyo-glossus, not always present. 
The stylo-glossus muscle arises beneath the parotid gland from the lower 
end of the styloid process and from the stylo-mandibular ligament. Proceeding 
forwards and inwards, it is inserted into the side and under partaee of the tongue, its 
fibres spreading out to decussate with those of the palato-glossus and hyo-g _clossus. 
The muscle is covered by the internal pterygoid muscle and the mucous membrane 
of the tongue. 
