_Origin_ by a strong tendon from the ventral border of the zygoma just
craniad of the mandibular fossa. The fibres pass cranioventrad, diverge
and have their
_Insertion_ into the external coronoid fossa.
_Relations._--Outer surface with the following, beginning at the caudal
border: the external ear, the parotid gland (Fig. 65, 1), the platysma,
the submentalis, the zygomaticus (major), the zygomaticus minor. Ventral
border with a lymph gland caudad of the angle of the mouth (Fig. 65, 3),
and the digastric muscle (_b_). Inner surface with the bones.
_Action._--A very powerful elevator of the lower jaw.
=M. temporalis= (Fig. 63, _n_).--The temporal muscle is the great mass
taking origin from the temporal fossa and having its insertion on both
surfaces and both borders of the coronoid process of the mandible. It
may be divided into two layers, deep and superficial.
The =superficial layer=. The temporal fascia stretches over the temporal
fossa, being attached to its borders; that is, to the sagittal and
lambdoidal crests, to the curved ridge which connects the sagittal crest
with the zygomatic process of the frontal bone, to the caudal border of
this process, to the caudal border of the malar bone, to the caudal
border of the ligament connecting the malar bone and the zygomatic
process of the frontal, and to the dorsal border of the zygomatic
process of the temporal bone and its dorsal root. The craniolateral part
of this fascia is much stronger than the remainder.
The muscle-fibres take origin from the strong craniolateral part of the
inner surface of the temporal fascia, from the groove on the temporal
bone dorsad of the dorsal root of its zygomatic process, from the whole
inner surface of this process and of the zygomatic process of the malar
bone, and sometimes also from that part of the frontal bone which lies
within the temporal fossa.
_Insertion.-_-The outer surface of the coronoid process of the mandible
dorsad of the coronoid fossa, and both borders of the coronoid process.
The cranial fibres may be inserted craniad of the coronoid process onto
the aponeurosis covering the deep portion of the muscle. The caudal part
of this portion is more or less distinct and is sometimes described as
a separate head.
The =deep portion=.
_Origin_ by fleshy fibres from the whole surface of the temporal fossa,
except in cases where the cranial part of the fossa is occupied by the
superficial portion. The fibres converge toward the coronoid process,
and the ventral third of the outer surface is covered by strong fascia.
_Insertion._--The whole inner surface of the coronoid process of the
mandible.
_Relations._--Outer surface with the external ear, the ear-muscles (Fig.
63), the epicranius (Fig. 63, _h_), the corrugatores supercilii
lateralis (_d_) and medialis (_b_). Inner surface with the skull, the
pterygoideus externus (Fig. 66, _b_), and the structures within the
orbit.
_Action._--Elevator of the lower jaw.
=M. pterygoideus externus= (Fig. 66, _b_).--This lies on the medial side
of the mandible, ventrad of the ventral portion of the temporal.
_Origin._--The external pterygoid fossa (Fig. 40, _h_), which lies on
the lateral surface of the perpendicular plate of the palatine bone, and
on the surface of the pterygoid process of the sphenoid bone dorsad of
the internal pterygoid fossa. The fossa extends from the foramen
rotundum to the sphenopalatine foramen. The muscle passes with parallel
fibres laterad, ventrad, and caudad and has its
_Insertion_ by a strong flat tendon into the medial surface of the
mandible near its ventral border between the opening of the mandibular
canal and the base of the angular process.
_Relations._--Ventral surface with the masseter (_a_), the digastric,
and the soft palate with its muscles. Dorsal surface with the temporal,
and near its origin with the muscles of the eye, and other structures in
the orbit.
_Action._--Elevator of the lower jaw.
=M. pterygoideus internus= (Fig. 66, _c_).--This lies caudad of the
pterygoideus externus, nearly parallel to it, and is connected with it
at its lateral end.
_Origin_ from the whole surface of the internal pterygoid fossa (Fig.
40, _s_).
_Insertion_ by fleshy fibres into the ventral surface of the external
pterygoid and its tendon, into the medial surface of the angular process
of the mandible and caudad of the angular process for about one
centimeter into a fascia common to it and the masseter muscle, and into
the stylomandibular ligament.
[Illustration: FIG. 66.--OBLIQUELY VENTRAL VIEW OF THE DEEP MUSCLES OF
THE LOWER JAW AND PALATE.
The tongue and other structures forming the floor of the mouth have
been removed, showing the roof of the mouth. On the right side the
masseter and pterygoideus internus have been removed, _a_, _a′_, M.
masseter; _b_, M. pterygoideus externus; _c_, M. pterygoideus
internus; _d_, _d′_, M. tensor veli palatini; _e_, _e′_, M. levator
veli palatini; _f_, M. constrictor pharyngis superior. 1, aponeurosis
of the velum palatinum; 2, ridges formed by the palatines and
pterygoid portions of the sphenoid; 3, hamular processes; 4, free
caudal border of the velum palatinum; 5, bulla tympani.]
_Relations._--Ventral surface with the styloglossus and the soft palate.
Dorsal surface with the bulla tympani (5) and base of the skull. Cranial
surface with the pterygoideus externus (_b_), with which it is partly
united.
_Action._--Assists the pterygoideus externus.
(_b_) _Muscles of the Hyoid Bone._
=M. stylohyoideus= (Fig. 65, _d_).--The stylohyoid is a ribbon-like
muscle about three millimeters wide. It lies on the superficial surface
of the digastric, caudad and ventrad of the angle of the jaw.
_Origin_ by fleshy fibres from the outer surface of the stylohyal bone
near its middle. The muscle curves over the outer surface of the
digastric (_b_), and ends about one centimeter from the middle line in a
slender flat tendon.
_Insertion_ into the middle of the ventral surface of the body of the
hyoid bone. Some of the fibres of the mylohyoid (_c_) are inserted into
its tendon.
_Relations._--Outer surface with the submaxillary gland (2) and the
submentalis muscle. Inner surface with the digastric (_b_), the
hyoglossus (Fig. 67, _h_), and the geniohyoid (Fig. 67, _g_).
_Action._--Raises the hyoid.
=M. geniohyoideus= (Fig. 67, _g_).--The geniohyoid is a long slender
muscle which lies next to the median line between the symphysis menti
and the hyoid bone, closely applied to its fellow of the opposite side
and within (dorsad of) the mylohyoid (Fig. 65, _c_).
_Origin_ from the ventral half of the inner surface of the mandibula for
about one millimeter from the symphysis.
_Insertion_ by muscle-fibres into the lateral half of the ventral
surface of the body of the hyoid bone.
_Relations._--Outer (ventral) surface with the stylohyoid (Fig. 65, _d_)
and the mylohyoid (Fig. 65, _c_); medial border with the muscle of the
opposite side. Lateral border with the hyoglossus (Fig. 67, _h_) and
genioglossus (Fig. 67, _f_). Inner (dorsal) surface with the
genioglossus.
_Action._--Draws the hyoid forward.
=M. jugulohyoideus= (Fig. 67, _b_).--The jugulohyoid is a small flat
quadrangular muscle covering the outer part of the ventral surface of
the tympanic bulla.
_Origin_ from the ventral border of the jugular process.
_Insertion_ into the caudal side of the cartilaginous part of the
stylohyoid opposite the origin of the styloglossus.
_Relations._--Ventral surface with the digastric. Dorsal surface with
the tympanic bulla (3).
_Action._--Draws the hyoid backward and thus gives a firmer surface of
origin for the styloglossus.
=M. mylohyoideus= (Fig. 65, _c_).--The mylohyoid is a large thin muscle
seen after the reflection of the digastric, filling with its fellow of
the opposite side the whole angle between the rami of the lower jaw. Its
fibres are transverse.
_Origin_ from the middle of the medial surface of the body of the
mandible between the caudal opening of the mandibular canal and the
symphysis of the jaw.
[Illustration: FIG. 67.--MUSCLES OF TONGUE, HYOID BONE, AND PHARYNX.
_a_, M. tragicus lateralis; _b_, M. jugulohyoideus; _c_, M.
pterygoideus externus; _d_, partially cut surface of M. pterygoideus
internus; _e_, M. styloglossus; _f_, M. genioglossus; _g_, M.
geniohyoideus; _h_, M. hyoglossus; _i_, M. glossopharyngeus; _j_, M.
constrictor pharyngis medius; _k_, M. constrictor pharyngis inferior;
_l_, M. stylopharyngeus; _m_, M. sternohyoideus (cut); _n_, M.
cricothyreoideus; _o_, M. sternothyreoideus (cut); _p_, M.
thyreohyoideus. 1, mandible; 1′, angular process of mandible; 2,
stylomandibular ligament; 3, bulla tympani; 4, trachea; 5, œsophagus;
6, thyroid gland; 7, isthmus of the thyroid gland.]
_Insertion_ with the opposite muscle into a median raphe which extends
from the symphysis of the jaw to the hyoid bone and is closely united to
the external surface of the geniohyoid. Some of the fibres gain
insertion into the body of the hyoid bone through their insertion into
the tendon of the stylohyoid (_d_).
_Relations_.--Outer surface with the submentalis (Fig. 64, _c_) and the
digastric (Fig. 65, _b_). Lateral edge with the masseter (_a_), the
digastric (_b_), and the mandibula. Caudal border with the stylohyoid
(_d_). Inner (dorsal) surface with the geniohyoid (Fig. 67, _g_), the
hyoglossus (Fig. 67, _h_), and the genioglossus (Fig. 67, _f_).
_Action_.--Raises the floor of the mouth and thus brings the hyoid
forward.
=M. ceratohyoideus.=
_Origin_, the two proximal pieces of the cranial horn of the hyoid. The
fibres pass caudad parallel to one another and within the middle
constrictor of the pharynx.
_Insertion_ into the whole length of the caudal cornu of the hyoid bone.
_Relations_.--Outer surface with the middle constrictor of the pharynx.
Inner surface with the pharynx.
_Action_.--Draws craniad the body of the hyoid by bringing its cornua
together and bending the joint between the two pieces of the cranial
cornua.
The muscles connecting the hyoid and the tongue are described in
connection with the description of the tongue.