Healthcare and Medicine Reference
Fig. 9.42 A cross-section through the neck
reveals the related but still distinct posterior,
middle, and anterior tracks of the DFL.
sternum. We emphasize once again that all three of these
tracks through the thorax are joined as one in the living
body, and are being separated here for analysis only.
This fascia includes the serrated fan of the transver-
sus thoracis muscle and by extension the entire plane of
endothoracic fascia in front of the viscera but behind the
costal cartilages (Fig. 9.43).
This line emerges from the rib cage just behind the
manubrium of the sternum. This myofascial line clearly
continues from this station with the infrahyoid muscles
- the sternohyoid express covering the sternothyroid,
thyrocricoid, and cricohyoid locals - up to the sus-
pended hyoid bone itself (Fig. 9.44).
This group is joined by that odd leftover from the
operculum, the omohyoid, which functions in speaking,
swallowing, and also to form a protective tent around
the jugular vein and carotid artery during strong con-
tractions of the surrounding neck muscles.
From the hyoid, the stylohyoid connects back to the
styloid process of the temporal bone. The digastric
muscle manages to go both up and forward to the chin
as well as up and back to the mastoid process. It even
manages to avoid dirtying its hands by touching the
hyoid at all - two slings of fascia reach up from the
hyoid, allowing the digastric to pull straight up on the
whole tracheal apparatus in swallowing. By these two
muscles, this most anterior branch of the DFL is con-
nected to the temporal bone of the neurocranium (Fig.
Two muscles, the mylohyoid and geniohyoid, accom-
pany the digastric in passing up and forward to the
inside of the mandible, just behind the chin. These two
form the floor of the mouth under the tongue. (It is
interesting to note the parallel between the construction
of the floor of the mouth and that of the floor of
the pelvis, in which the geniohyoid equates with the
pubococcygeus, and the mylohyoid equates with the
From these hyoid muscles, we could claim a mechan-
ical connection through the mandible (though a direct
fascial connection is a little harder to justify) with the
muscles which close the jaw (Fig. 9.46). The masseter,
which lifts up from the zygomatic arch, and the medial
pterygoid, which lifts up from the underside of the
Fig. 9.43 This upper anterior track includes the transversus
thoracis, that odd muscle on the inside of the front of the ribs
which supports the costal cartilages and can contract the chest
when we are cold.
Fig. 9.44 The infrahyoid muscles emerge from behind the
sternum, joining the inside of the ribs to the front of the throat and
the hyoid bone.