Part 11

_Origin_ from the middle line of the neck dorsad of the atlas, and from the sagittal crest for about one centimeter craniad of the external occipital tubercle. The fibres form a broad thin sheet which passes craniolaterad as far as the caudal end of the scutiform cartilage (1). Here the muscle divides; the major portion is attached to the scutiform cartilage (1), its fibres intermingling with those of the intermedius scutulorum (_a_). The caudal portion of the muscle (_g′_) passes onto the surface of the auricle, extending one or two centimeters distad; here it is inserted on an oblique line which lies directly craniad of the insertion of the transversus auriculæ (_i_).

The caudal portion of this muscle (_g′_) having origin above the atlas and insertion on the auricle, is sometimes considered a separate muscle, the supercervicoauricular or cervicoauricular. The cranial portion (_g_) with origin on the sagittal crest and insertion on the scutiform cartilage might be distinguished as the occipitoscutularis.

The levator auris longus is continuous at its cranial end medially with M. epicranius (_h_); laterally with M. intermedius scutulorum (_a_).

_Relations._--Outer surface with the integument. Inner surface with the temporal muscle (_n_), the auricularis superior (_k_), the abductor longus auris (_m_), a narrow strand of the platysma, and the clavotrapezius.

_Action._--Pulls the external ear dorsocaudad.

The four following muscles lie partly or entirely beneath those already described; they are doubtless formed as differentiations of the inner layers of the platysma.

=M. auricularis superior= (or attollens auris) (Fig. 63, _k_).--This muscle forms a band about one centimeter broad lying just beneath the levator longus (_g_).

_Origin_ on the sagittal crest for about one centimeter craniad of the interparietal bone. The muscle passes laterad onto the surface of the auricle and is inserted into the auricular cartilage a little caudad of the middle of its convex surface. At its lateral end the cranial margin is closely united to the under surface of the levator auris longus (_g_).

_Relations._--Outer surface at the medial end with the epicranius (_h_), the abductor auris longus (_m_), and levator auris longus (_g_); at the lateral end with the skin. Inner surface with the temporal muscle (_n_) and the auricular cartilage.

_Action._--Pulls the external ear dorsad.

=M. abductor auris longus= (Fig. 63, _m_; Fig. 64, _q_). (Part of the auricularis posterior of man.)

_Origin_ on the sagittal crest dorsad of the interparietal bone, caudad of that of the auricularis superior (_k_), which it partly covers.

The muscle passes laterad as a flat band 8 to 10 millimeters wide over the caudal surface of the concha of the ear, and is inserted (Fig. 64, _q_) on the lateral surface of the eminentia conchæ, caudad of the antitragus.

_Relations._--Outer surface with the levator auris longus (_g_) and the integument. Inner surface with the auricularis superior (_k_), the abductor auris brevis (_l_), and the concha.

_Action._--Pulls the external ear caudad.

=M. abductor auris brevis= (Fig. 63, _l_).

_Origin_ by a tendon from the lambdoidal crest for one or two centimeters laterad of the middle.

The muscle passes lateroventrad lying beneath the abductor longus (_m_) as a flat band 6 to 8 millimeters wide which is inserted into the medial surface of the most proximal portion of the concha, just distad of its junction with the cartilaginous auditory meatus.

_Relations._--Outer surface with the abductor longus (_m_), a small strand of the platysma and the concha. Inner surface with the temporal muscle (_n_).

_Action._--Pulls the concha caudad.

=M. epicranius= (or occipitofrontalis) (Fig. 63, _h_ and _h′_).

_Origin_ on the sagittal crest or suture, just craniad of the origin of the levator longus auris, to the inner surface of which this muscle is closely united. From the origin the fibres pass craniad forming a band (_h_) about 8 or 10 millimeters in width, the two muscles lying close to one another and partly united in the middle line. About two centimeters craniad of their origin the fibres of both muscles end in a tendinous sheet, the =galea aponeurotica=, which covers the surface of the skull in the region between the ears and eyes, and is formed by the inner surface of the intermedius scutulorum (_a_) and other muscles of this region. The galea aponeurotica passes craniad onto the surface of the nose, where it gives origin again to a thin sheet of muscle-fibres (_h′_) which are inserted into the integument near the cranial ends of the nasal bones.

M. epicranius is thus formed of two muscular portions (_h_ and _h′_), connected by a long tendinous sheet. The caudal portion is frequently distinguished as the occipital muscle (=M. occipitalis=, _h_), the cranial portion, on the nose, as the =frontal= muscle (=M. frontalis=, _h′_).

_Relations._--Outer surface of the occipitalis (_h_) with the intermedius scutulorum (_a_), the levator auris longus (_g_), and the integument; inner surface with the auricularis superior (_h_), the abductor auris longus, and the bone. Outer surface of the frontalis (_h′_) with the integument; inner surface with the bones of the skull.

_Action._--Moves the integument of the dorsal surface of the head and of the nose.

Ventrad of the external ear the following three differentiated portions of the platysma may be distinguished.

=M. zygomaticus= (major) (Fig. 64, _d_).--A slender band connecting the angle of the mouth with the scutiform cartilage of the ear.

At the angle of the mouth the fibres arise from among those of the orbicularis oris (_i_), from both the upper and the lower lip. They pass thence dorsocaudad across the zygomatic arch as a band 8 or 10 millimeters wide which is attached to a tendinous aponeurosis lying just craniad of the external opening of the ear. To this aponeurosis are attached also, wholly or partly, the corrugator supercilii lateralis (_k_) and the submentalis (_c_). The aponeurosis is united with the caudoventral angle of the scutiform cartilage and with the ventral edge of the cranial margin of the auricular cartilage.

This muscle is united at its cranial end with the orbicularis oris (_i_); throughout its length more or less with the platysma (_a_, _a′_); at its caudodorsal end with the corrugator supercilii lateralis (_k_) on its medial side, and with the submentalis (_c_) on its lateral side.

_Relations._--Outer surface with the integument and the platysma (_a′_). Inner surface with the masseter, temporal, frontoscutularis, and adductor auris inferior (_o_).

_Action._--Draws the angle of the mouth dorsocaudad; the external ear ventrocraniad.

=M. submentalis= (Fig. 64, _c_).--A flat band, similar to the last, and closely connected for some distance to its caudal border.

It arises as scattered fibres near the ventral middle line at about the level of the larynx, the fibres of the opposite muscles crossing the middle line and intermingling. The fibres pass dorsad, converging so as to form a narrower band, which unites dorsad with the zygomaticus (_d_), to be inserted with it into the tendinous aponeurosis above described.

_Relations._--Outer surface with the integument and platysma (_a′_). Inner surface with the muscles of the hyoid, the digastricus, the parotid gland, the masseter, the zygomatic arch and the temporal muscle.

_Action._--Draws the external ear ventrad.

=M. depressor conchæ= (Fig. 64, _b_).--A thin band of fibres, caudad of the last and parallel with it. The muscle arises as scattered fibres on the ventral surface of the neck, one or two centimeters craniad of the manubrium, the fibres of the muscles of opposite sides crossing the middle line and interdigitating. They pass dorsad, gathering together to form a narrow band which is inserted into the summit of the antitragus.

_Relations._--Outer surface with the skin at the ventral end, and with the platysma (_a′_) further dorsad. Inner surface with the deep muscles of the neck and with the parotid gland.

_Action._--Draws the external ear ventrad.

Lying deeper than the muscles thus far described, but closely connected with a number of them, are the following:

=M. frontoscutularis.=

_Origin_ (Fig. 63, _o_) on the frontal bone, along the supraorbital margin, from the craniomedial angle of the eye caudad to the zygomatic process of the frontal.

The fibres form a large muscle which passes dorsocaudad to the scutiform cartilage and is mostly attached along its ventrolateral border. Some of the outer fibres, however, pass distad of the scutiform cartilage toward the cartilage of the ear, thus joining the adductor auris superior (_f_).

The outer surface of this muscle is closely connected with fibres of the intermedius scutulorum (_a_), the corrugatores supercilii medialis (_b_) and lateralis (_d_), and the frontoauricularis, when this exists. The outer surface is covered near the origin by the orbicularis oculi (_c_), farther dorsad by the muscles just mentioned and the integument. The inner surface is in relation with the frontal bone and the adductor auris inferior (Fig. 64, _o_).

_Action._--Pulls the ear craniad.

=M. adductor auris inferior.= (Fig. 64, _o_.) (Part of the auricularis anterior of man.)--A small muscle lying beneath the frontoscutularis.

_Origin_ on the ligament which connects the zygomatic process of the frontal with the frontal process of the malar. The fibres form a thin band about 7 millimeters wide which passes craniad, closely united to the inner surface of the frontoscutularis. At the caudal edge of the zygomaticus (_d_) the muscle is interrupted by a short tendinous interval; the fibres then continue to their insertion on the tip of the antitragus.

_Relations_.--Outer surface with the frontoscutularis, the zygomaticus (_d_), and the integument. Inner surface with the temporal muscle and M. antitragicus (_n_).

_Action._--Pulls the ear craniodorsad.

* * * * *

The remainder of the muscles of the ear, which, with the exception of the tragicus lateralis, merely interconnect the cartilages of the external ear or parts of these cartilages, are described in connection with the account of the Auditory Organ.

* * * * *

Owing to the presence of the fibrous pad to which the whiskers are attached, the facial muscles between the eye and the mouth differ in the cat in some respects from those of related animals. This fibrous pad interrupts the muscles, frequently breaking muscles which are elsewhere single into two.

=M. zygomaticus minor=, or malaris (Fig. 64, _e_).--This muscle is not always present; when it exists it forms a very thin flat band of fibres passing from the ventral side of the eye toward the angle of the mouth.

_Origin_ among the fibres of the orbicularis oculi (_s_) in the lower eyelid. The fibres pass ventrad; the insertion varies. In some specimens the insertion is among the fibres of the orbicularis oris (_i_), at the angle of the mouth, beneath the zygomaticus (_d_). In other cases this muscle is said to be inserted into the pad on which the whiskers rest.

_Relations._--Outer surface with the integument and near its insertion with the zygomaticus major (_d_). Inner surface with the malar bone and the masseter muscle.

_Action._--Pulls the angle of the mouth (or the whiskers) dorsad.

=M. orbicularis oris= (Fig. 64, _i_).--This forms a very thin layer of subcutaneous concentric fibres which surround the mouth, that of the upper lip being thicker than that of the lower lip. The part of the muscle in the lower lip has its fibres intermingled with those of the platysma (_a′_). In the median line the fibres of the upper lip are interrupted by a raphe, and caudad of this are intermingled with those of the caninus.

=M. quadratus labii superioris= (Fig. 63, _p_ and _q_; Fig. 64, _f_ and _g_).--This is a complex of muscle-fibres attached chiefly to the fibrous pad on which the whiskers rest. In it two parts can be distinguished more or less completely.

(1) =M. levator labii superioris alæque nasi= (Fig. 63, _p_; Fig. 64, _g_) on the sides of the nose. This arises (_a_) as a continuation of the frontal portion of the epicranius, and (_b_) in a small bundle (Fig. 63, _p_) from near the dorsal end of the frontal process of the maxillary bone, in common with the next. The two slips thus formed unite craniad and are inserted partly into the integument on the outer side of the wing of the nose, partly into the skin of the upper lip, lateroventrad of the nose, and partly into the pad on which the whiskers are located, in connection with the next.

(2) The =angular= head (=caput angulare=), or =levator labii superioris proprius= (Fig. 63, _q_; Fig. 64, _f_) is much larger than the last. It takes origin from a small tubercle at the cranial border of the orbit, close to the origin of the orbicularis oculi. The fibres diverge from their origin to their insertion among the whiskers and in the fibrous pad on which the whiskers rest.

_Action._--Erects the whiskers and raises the upper lip.

=M. caninus= or =levator anguli oris= (Fig. 64, _f′_).

_Origin_ in a depression on the lateral surface of the maxillary bone, just craniad of the last premolar tooth. The fibres pass craniad, diverging, toward the whiskers, and have their insertion into the pad of tissue on which the whiskers rest.

_Action._--Retracts the whiskers and raises the upper lip.

=M. buccinator.=--A thin muscle against the mucous membrane of the upper lip, partly united with the orbicularis oris and lying beneath M. caninus.

_Origin_ on the outer surface of the superior maxillary bone in the depression between the infraorbital foramen and the first premolar tooth. The fibres pass ventrad, diverging, and mingle with those of the deep part of the orbicularis oris.

_Relations._--Outer surface with the caninus and with the orbicularis oris. Inner surface with the mucous membrane of the upper lip.

_Action._--Raises the upper lip.

=M. myrtiformis= (probably corresponds to a part of the human M. nasalis) (Fig. 64, _h_).--A thin sheet of muscle-fibres lying craniad of the levator labii superioris alæque nasi and passing from the whiskers to the nose and upper lip. It is distinguishable from the alæque nasi by the direction of the fibres.

_Origin_ from the pad upon which the whiskers rest. The fibres diverge and have their

_Insertion_ upon the wing of the nose and into the skin of the upper lip near the median line.

_Action._--Dilator of the nares and elevator of the upper lip.

=M. “moustachier”= (Str.-D.) (probably corresponds to one of the Mm. incisivi).--It lies on the upper lip near the median line.

_Origin_ from the outer surface of the premaxilla near the suture along the ventral border of the narial opening. The fibres diverge and pass caudad into the upper lip within the superficial fibres of the orbicularis oris.

_Insertion._--The skin of the upper lip just craniad of the whiskers. Some of the fibres pass into the pad on which the whiskers rest.

_Action._--It carries the lip craniad.

=M. quadratus labii inferioris.=--A thin flat band extending almost the length of the lower lip.

_Origin_ from the alveolar border of the mandible, between the molar tooth and the canine. The fibres pass dorsad into the lower lip, where they intermingle with those of the orbicularis oris. The muscle is perhaps not constant.

_Action._--Depressor of the lower lip.

Sometimes a few fibres arising from the cranial portion of the alveolar border of the mandibula pass mediad, seeming to join corresponding fibres from the opposite side. Such fibres would constitute a M. transversus menti.

B. DEEP MUSCLES OF THE HEAD.

(_a_) _Muscles of Mastication._

=M. digastricus= (Fig. 65, _b_).--The digastric is a thick prismatic muscle lying mediad of the angle of the lower jaw, connecting it with the base of the skull.

_Origin_ by fleshy fibres from the outer surface of the jugular process of the occipital bone, and by a thin tendon from the tip of the mastoid process and from the ridge between the mastoid and the jugular processes. The muscle passes craniad, becoming at the same time broader and more voluminous.

_Insertion._--The ventral border of the mandible craniad of the caudal border of the molar tooth. The insertion area extends slightly onto both surfaces of the bone and is triangular, with its apex craniad.

_Relations._--Outer (ventral) surface with the following, beginning at the caudal end: the rectus capitis lateralis, the cleidomastoid (_h_), the submaxillary gland (2), the stylohyoid (_d_), a large lymph-gland (3), and the integument. Inner (dorsal) surface with the jugulohyoid, the tympanic bulla, the masseter (_a_), the hyoglossus, and the mylohyoid (_c_).

_Action._--Depressor of the lower jaw.

=M. masseter= (Figs. 65 and 66, _a_).--The masseter forms the projecting mass so prominent in the cat behind and below the eye. Its outer surface is covered by a strong aponeurosis. The muscle is divided into three layers which are distinct as to origin, insertion, and direction of fibres, but which are otherwise not distinct.

The =superficial layer= takes

_Origin_ by the superficial aponeurosis from the ridge which runs lengthwise of the outer surface of the malar bone, and by fleshy fibres from the surface of the malar bone ventrad of this ridge. The fibres pass obliquely caudad to their insertion.

_Insertion._--The caudal half of the lateral margin of the ventral border of the mandible, by a sheet of fascia which lies on the inner surface of the muscle. The superficial fibres curve ventrad of the mandible and are inserted into a tendinous intersection between this muscle and the internal pterygoid (Fig. 66, _c_).

The =middle layer= takes

_Origin_ from the ventral border of the malar bone, from opposite the molar tooth to within three millimeters of the mandibular fossa. The fibres pass ventrad and have their

_Insertion_ into the mandible at the ventral border of the external coronoid fossa by means of the aponeurosis which covers the inner surface of the muscle.

The =deep layer= takes

_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.