Myology1
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MyologyIntroductionMuscles are of three types—skeletal muscle, smooth muscle and cardiac muscle. This chapter focuses on skeletal muscle.1.Structure The muscles are connected with the bones, cartilages, ligaments,and skin, either directly, or through the intervention of fibrous structures called tendons or aponeuroses. Where a muscle is attached to bone or cartilage, the fibers end in blunt extremities upon the periosteum or perichondrium, and do not come into direct relation with the osseous or cartilaginous tissue. Where muscles are connected with its skin, they lie as a flattened layer beneath it, and are connected with its areolar tissue by larger or smaller bundles of fibers, as in the muscles of the face. The muscles vary extremely in their form. In the limbs, they are of considerable length, especially the more superficial ones;they surround the bones, and constitute an important protection to the various joints. In the trunk, they are broad, flattened, and expanded, and assist in forming the walls of the trunk cavities.2.Muscle NamingThe names applied to the various muscles have been derived: (1) from their situation, as the Tibialis, Radialis, Ulnaris, Peronæus; (2) from their direction, as the Rectus abdominis, Obliqui capitis, Transversus abdominis; (3) from their uses, as Flexors, Extensors, Abductors, etc.; (4) from their shape, as the Deltoideus, Rhomboideus; (5) from the number of their divisions, as the Biceps and Triceps;(6) from their points of attachment, as the Sternocleidomastoideus,Sternohyoideus, Sternothyreoideus. In the description of a muscle, the term origin is meant to imply its more fixed or central attachment; and the term insertion the movable point on which the force of the muscle is applied; but the origin is absolutely fixed in only a small number of muscles, such as those of the face which are attached by one extremity to immovable bones, and by the other to the movable integument; in the greater number, the muscle can be made to act from either extremity.3. Muscle attachmentFascia The fascia are fibroareolar or aponeurotic laminæ, of variable thickness and strength, found in all regions of the body, investing the softer and more delicate organs. During the process of development many of the cells of the mesoderm are differentiated into bones, muscles, vessels, etc.; the cells of the mesoderm which are not so utilized form an investment for these structures and are differentiated into the true skin and the fasciæ of the body.They have been subdivided, from the situations in which they occur, into superficial and deep. The superficial fascia is found immediately beneath the integument over almost the entire surface of the body. It connects the skin with the deep fascia, and consists of fibroareolar tissue, containing in its meshes pellicles of fat in varying quantity. The deep fascia is a dense, inelastic, fibrous membrane, forming sheaths for the muscles, and in some cases affording them broad surfaces for attachment. It consists of shining tendinousfibers, placed parallel with one another, and connected together by other fibers disposed in a rectilinear manner.Synovial bursaTendinous sheath Tendons are white, glistening, fibrous cords, varying in length and thickness, sometimes round, sometimes flattened, and devoid of elasticity. They consist almost entirely of white fibrous tissue, the fibrils of which have an undulating course parallel with each other and are firmly united together. They are very sparingly supplied with bloodvessels, the smaller tendons presenting in their interior no trace of them. Nerves supplying tendons have special modifications of their terminal fibers, named organs of Golgi.Muscles of the TrunkMuscles of Facial ExpressionMuscles of Mastication1.BackErector Spinae MusclesMuscles that act on the ThighLeg Musculature Muscles of the abdominal wallo Insertion:▪▪(via 4 tendons and giving a fibrous expansion) o Action:0.1.weak dorsiflexor & everts footo Blood: anterior tibial arteryo Nerve:, L4,5,S1∙ Tibialis anterioro Origin:teral tibial condyle2.proximal 2/3 of anteriolateral surface of tibia3.interosseous membrane4.anterior intermuscular septum & crural fasciao Insertion:1.2.medial & plantar surface of the cuneiformo Action:1.strongest dorsiflexor2.o Blood: anterior tibial arteryo Nerve:, L4,5,S1∙o Origin:1.2.distal & lateral aspect of extensor digitorumo Insertion:o Action:1.2.weak dorsiflexor & everts footo Blood: anterior tibial arteryo Nerve:, L4,5,S1∙o Origin:1.2.proximal 2/3 of anteriolateral surface of tibia3.interosseous membrane4.anterior intermuscular septum & crural fasciao Insertion:1.medial & plantar surface of base of 1st metatarsal2.medial & plantar surface of the cuneiformo Action:1.strongest dorsiflexor2.inverts & adducts the footo Blood: anterior tibial arteryo Nerve: deep peroneal nerve, L4,5,S1∙o Origin:1.2.proximal 2/3 of lateral fibula3.adjacent intermuscular septumArticularis genus∙Origin:1.distal portion of anterior femoral surface, close to the knee2.off the deep fibers of the vastus intermedius∙Insertion: synovial membrane of the knee joint∙Action:1.pulls the synovial membrane of the knee superior with knee extension2.prevents impingement of the synovial membrane between patella and the femur∙Blood: lateral femoral circumflex artery∙Nerve: branches of femoral nerve, L3,4Psoas major∙Origin:1.transverse processes of L1-L52.vertebral bodies of T12-L4 and the intervening intervertebral discs∙Insertion: iliopsoas tendon to the lesser trochanter of the femur∙Action:1.hip flexionteral rotation∙Blood: muscular branches of medial femoral circumflex artery∙Nerve: ventral rami, L1,2,3Pectineus∙Origin:1.pectineal line of the pubis2.superior pubic ramus∙Insertion:o the pectineal line of the femuro(just below the lesser trochanter on the posterior aspect of the femur) ∙Action:0.flexes hip1.adducts thigh2.medially rotates thigh∙Blood: muscular branches of medial femoral circumflex artery∙Nerve:o femoral nerve, L3,4 ORo obturator nerve, L2,3,4 ORo femoral L3,4 and accessory obturator L3,4Obturator externus∙Origin:1.medial surface of obturator foramen2.external surface of obturator membrane∙Insertion: trochanteric fossa of femur∙Action:terally rotates thigh2.assists in flexion of hip joint∙Blood: obturator artery∙Nerve: obturator nerve, L2,3,41.Spi∙Origin:1.humeral head - via the CFT (common flexor tendon)2.ulnar head:a.b.proximal 3/5 of dorsal ulnar shaftc.antebrachial fascia∙Insertion:1.pisiform & hamate bones (via the pisohamate ligament)2.base of the 5th (via the pisometacarpal ligament)∙Action:1.flexes the hand at the wrist2.ulnarly deviates the wrist3.stabilizes wrist to permit powerful thumb motion∙Blood: muscular branches of ulnar artery∙Nerve:, C8,T1nalis cervicis∙Origin: spinous processes of C6-T2∙Insertion: spinous processes of C2 (and possibly extend to C3 or C4)∙Action: (same for all erector spinae)1.bilateral:a.extension of vertebral columnb.maintenance of erect posture (pneumonic = I Like S tanding)c.stabilization of vertebral column during flexion, acting incontrast to abdominal muscles and the action of gravity2.unilateral:teral bend to same sideb.rotation to same sidec.opposite muscles contract eccentrically for stabilization∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nervesSpinalis capitis∙Origin: spinous processes of lower cervical & upper thoracic vertebrae∙Insertion: between superior & inferior nuchal lines of occipital bone∙Action: (same for all erector spinae)1.bilateral:a.extension of vertebral columnb.maintenance of erect posture (pneumonic = I Like S tanding)c.stabilization of vertebral column during flexion, acting incontrast to abdominal muscles and the action of gravity2.unilateral:teral bend to same sideb.rotation to same sidec.opposite muscles contract eccentrically for stabilization∙Blood: muscular branches of the aorta∙.Multifidus. Origin:o cervical region: from articular processes of lower cervical vertebraeo thoracic region: from transverse processes of all thoracic vertebraeo lumbar region:1.lower portion of dorsal sacrum2.PSIS3.deep surface of tendenous origin of erector spinae4.mamillary processes of all lumbar vertebrae∙Insertion: spinous process of all vertebrae extending from L5 - C2 (skipping 1-3 segments)∙Action:1.bilaterally extends vertebral column2.controls lateral flexion to side opposite contraction (eccentric forstability)3.unilaterally rotate vertebral bodies (column) to opposite side∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nervesRotatores. Long rotators∙Origin: transverse process of one vertebra∙Insertion: skips one vertebra to insert on the base of spinous process of vertebra above∙Action:1.rotate to opposite side2.bilateral extension∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nervesShort rotators∙Origin: transverse process of one vertebra∙Insertion: base of spinous process of vertebra immediately above∙Action:1.rotate to opposite side2.bilateral extension∙Blood: muscular branches of the aortaInterspinalis∙Origin: spinous processes of each vertebra∙Insertion: to the spinous process of vertebra immediately above∙Action: extension of the vertebrae segments∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nerves∙Sacrospinalis.Semispinalis.Semispinalis thoracis∙Origin: transverse processes of T6-T12 vertebrae∙Insertion: spinous processes of upper thoracic & lower cervical vertebrae∙Action:1.bilaterally extends vertebral column, especially head and neck2.controls lateral flexion to side opposite contraction (eccentric forstability)3.maintains head posture∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nervesSemispinalis cervicis∙Origin: transverse processes of T1-T6 vertebrae and can go down to lower thoracic∙Insertion: spinous processes of C2-T5(6)∙Action:1.bilaterally extends vertebral column, especially head and neck2.controls lateral flexion to side opposite contraction (eccentric forstability)3.maintains head posture∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nervesSemispinalis capitus∙Origin:1.transverse processes of T1-T62.articular processes of C4-C7∙Insertion: between superior & inferior nuchal lines of occipital bone∙Action:1.bilaterally extends vertebral column, especially head and neck2.controls lateral flexion to side opposite contraction (eccentric forstability)3.maintains head posture∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nerves∙∙Intertransversarii∙Origin: (A to A and B to B)o cervical region:A.from the anterior tubercle of transverse processB.from the posterior tubercle of transverse processo thoracic region: (poorly developed)o lumbar region:teral aspect of the transverse processB.mamillary process∙Insertion:o cervical region:A.to the anterior tubercle immediately aboveB.to the posterior tubercle immediately aboveo thoracic region: (poorly developed)o lumber region:teral aspect of the transverse process immediately aboveB.to the accessory process on the vertebra immediately above∙Action:terally flexes each respective pair of vertebrae2.(also eccentric muscle contraction provides stability)∙Blood: muscular branches of the aorta∙Nerve: dorsal rami of spinal nerves2.NeckThe Superficial Cervical MuscleThe Platysma(Fig. 378)is a broad sheet arising from the fascia covering the upper parts of the Pectoralis major and Deltoideus; its fibers cross the clavicle, and proceed obliquely upward and medialward along the side of the neck. The Sternocleidomastoideus(Sternomastoid muscle) (Fig. 385)passes obliquely across the side of the neck. It is thick and narrow at its central part, but broaderand thinner at either end. It arises from the sternum and clavicle by two heads.The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the manubrium sterni, and is directed upward, lateralward, and backward. The lateral or clavicular head,composed of fleshy and aponeurotic fibers, arises from the superior border and anterior surface of the medial third of the clavicle; it is directed almost vertically upward. The two heads are separated from one another at their origins by a triangular interval, but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.hyoid musclesThe suprahyoid muscles (Figs) are: 1 Digastricus.Mylohyoideus.Stylohyoideus.Geniohyoideus.The infrahyoid muscles are: 14 Sternohyoideus.Thyreohyoideus.Sternothyreoideus.Omohyoideus.The deep Cervical MuscleScalenus anterior.Scalenus medius.Scalenus posterior. Anterior scalene∙Attachment A: anterior tubercles of transverse processes of C3-C6∙Attachment B: 1st rib∙Action:if transverse process fixed:1.elevates the ribs for respirationif ribs fixed:2.rotates to side opposite of contractionterally flexes to the contracted side4.bilaterally flexes the neck∙Blood: inferior thyroid artery (branch of the thyrocervical trunk)∙Nerve: ventral rami C3-C6Scalenus minimus (may be absent)∙Attachment A: anterior tubercles of transverse processes of C6 & 7∙Attachment B: 1st rib and/or supraplural membrane∙Action:if transverse process fixed:1.elevates the ribs for respirationif ribs fixed:2.rotates to side opposite of contractionterally flexes to the contracted side4.bilaterally flexes the neck∙Blood: ascending cervical artery∙Nerve: variable (cervical and brachial plexus)Middle scalene∙Attachment A: transverse processes of all cervical vertebrae∙Attachment B: 1st rib (behind anterior scalene)∙Action:if transverse process fixed:1.elevates the ribs for respirationif ribs fixed:2.rotates to side opposite of contractionterally flexes to the contracted side4.bilaterally flexes the neck∙Blood: ascending cervical artery∙Nerve: ventral rami C3-C8Posterior scalene∙Attachment A: posterior tubercles of transverse processes of C5 & C6 ∙Attachment B: 2nd and/or 3rd rib∙Action:if transverse process fixed:1.elevates the ribs for respirationif ribs fixed:2.rotates to side opposite of contractionterally flexes to the contracted side4.bilaterally flexes the neck∙Blood: ascending cervical artery∙Nerve: ventral rami C5-C73.ThoraxPectoralis major.∙Origin:1.medial 1/3 of clavicle2.anterior aspect of manubrium & length of body of sternum3.cartilaginous attachments of upper 6 ribs4.external oblique's aponeurosis∙Insertion:teral lip of bicipital groove to the crest of the greater tubercle2.clavicular fibers insert more distally; sternal fibers more proximally∙Action:1.adducts humerus2.medially rotates humerus3.flexion of the arm from extension (clavicular portion)∙Blood:1.pectoralis branch of thoracoacromial artery (runs with lateral pec.nerve)teral thoracic artery (lesser supply, and runs with medial pectoralnerve)∙Nerve:teral pectoral nerve, C5,6,7 to clavicular portion2.medial pectoral nerve, C8,T1 to sternal portion∙Intercostales externi.Intercostales interni.4.Diaphragm5.AbdomenThe muscles of the abdomen may be divided into two groups: (1) the anterolateral muscles; (2) the posterior muscles.1. the Antero-lateral Muscles of the Abdomen—The muscles of this group are: Obliquus externus.Transversus.Obliquus internus.Rectus.PyramidalisThe Posterior Muscles of the AbdomenPsoas major.Iliacus.Psoas minor.Quadratus lumborumMuscles of the Head1.FacialEpicranius is a broad, musculofibrous layer, which covers the whole of one sideof the vertex of the skull, from the occipital bone to the eyebrow. It consists oftwo parts, the Occipitalis and the Frontalis, connected by an interveningtendinous aponeurosis, the galea aponeurotica.The Orbicularis oculi arises from the nasal part of the frontal bone, from thefrontal process of the maxilla in front of the lacrimal groove, and from theanterior surface and borders of a short fibrous band, the medial palpebralligament.From this origin, the fibers are directed lateralward, forming a broadand thin layer, which occupies the eyelids or palpebræ, surrounds thecircumference of the orbit, and spreads over the temple, and downward on thecheek.The Orbicularis oris(Fig. 381)is not a simple sphincter muscle like theOrbicularis oculi; it consists of numerous strata of muscular fibers surroundingthe orifice of the mouth but having different direction. It consists partly of fibersderived from the other facial muscles which are inserted into the lips, and partlyof fibers proper to the lips.The muscles of the nose (Fig. 378). comprise: 1 Procerus.Depressor septi.Nasalis.Dilatator naris posterior.Dilatator naris anterior.2.MasticationThe chief muscles of mastication are:Masseter.The Masseter(Fig. 378) is a thick, somewhat quadrilateral muscle, consisting oftwo portions, superficial and deep.Temporalis.is a broad, radiating muscle, situated at the side of the head.It arises from the whole of the temporal fossa (except that portion of it which isformed by the zygomatic bone) and from the deep surface of the temporal fascia. Its fibers converge as they descend, and end in a tendon, which passes deep to the zygomatic arch and is inserted into the medial surface, apex, and anterior border ofthe coronoid process, and the anterior border of the ramus of the mandible nearly asfar forward as the last molar tooth.Pterygoideus internus The Pterygoideus internus (Internal pterygoid muscle) (Fig. 383) is a thick, quadrilateral muscle. It arises from the medial surface of the lateral pterygoid plate and the grooved surface of the pyramidal process of the palatine bone;it has a second slip of origin from the lateral surfaces of the pyramidal process of the palatine and tuberosity of the maxilla. Its fibers pass downward, lateralward, and backward, and are inserted, by a strong tendinous lamina, into the lower and backpart of the medial surface of the ramus and angle of the mandible, as high as the mandibular foramen..The Pterygoideus externus (External pterygoid muscle) (Fig. 383) is a short, thick muscle, somewhat conical in form, which extends almost horizontally between the infratemporal fossa and the condyle of the mandible. It arises by two heads; anupper from the lower part of the lateral surface of the great wing of the sphenoid and from the infratemporal crest; a lower from the lateral surface of the lateral pterygoid plate. Its fibers pass horizontally backward and lateralward, to be inserted into a depression in front of the neck of the condyle of the mandible, and into the front margin of the articular disk of the temporomandibular articulation.Muscles of the Upper Extremity1.girdle muscles of the Upper extremityIn this group are included: 1 Deltoideus.∙Origin:teral, anterior 1/3 of distal clavicleteral boarder of the acromion3.scapular spine∙Insertion: deltoid tuberosity of humerus∙Action:1.abducts arm2.flexion and medial rotation (anterior portion)3.extension and lateral rotation (posterior portion)∙Blood:1.posterior humeral circumflex artery2.deltoid branch of thoracoacromial artery∙Nerve: axillary nerve, C5,6Infraspinatus. Infraspinatus∙Origin:1.infraspinous fossa2.muscle fascia∙Insertion: middle facet of greater tubercle of humerus∙Action:1.external rotation of the humerus2.stabilizes the glenohumeral joint∙Blood:1.suprascapular artery2.scapular circumflex artery∙Nerve: suprascapular nerve, C5,6Subscapularis. Subscapularis∙Origin: subscapular fossa∙Insertion: lesser tubercle of humerus∙Action:1.medial rotation of the humerus2.stabilizes the glenohumeral joint∙Blood: Branches of subscapular artery∙Nerve: upper & lower subscapular nerves, C5,6Teres minor. Teres minor∙Origin: middle half of the scapula抯lateral margin∙Insertion: lowest of three facets of the greater tubercle of humerus∙Action:teral rotation of the humerus2.stabilizes the glenohumeral joint∙Blood: scapular circumflex artery∙Nerve: axillary nerve, C5,6Supraspinatus.∙Origin:1.supraspinous fossa2.muscle fascia∙Insertion: uppermost of three facets of the greater tubercle of humerus∙Action:1.abduction of arm (first 15-20?2.stabilizes glenohumeral joint∙Blood: suprascapular artery (poorly supplied)∙Nerve: suprascapular nerve, C5,6Teres major. Teres major∙Origin: inferior, lateral margin of the scapula∙Insertion: crest of lesser tubercle (just medial to the insertion of latissimus dorsi)∙Action:1.assists in adduction of arm2.assists in medial rotation of arm3.assists in extension from an flexed position∙Blood: thoracodorsal artery∙Nerve: lower subscapular nerve, C5,6The Deltoideus (Deltoid muscle) (Fig. 410) is a large, thick, triangular muscle, which covers the shoulder-joint in front, behind, and laterally. It arises from the anterior border and upper surface of the lateral third of the clavicle; from the lateral margin and upper surface of the acromion, and from the lower lip of the posterior border of the spine of the scapula, as far back as the triangular surface at its medial end.The Supraspinatus(Fig. 412) occupies the whole of the supraspinatous fossa, arising from its medial two-thirds, and from the strong supraspinatous fascia. The muscular fibers converge to a tendon, which crosses the upper part of the shoulder-joint, and is inserted into the highest of the three impressions on the greater tubercle of the humerus; the tendon is intimately adherent to the capsule of the shoulder-joint.The Infraspinatus(Fig. 412) is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa; it arises by fleshy fibers from its medial two-thirds, and by tendinous fibers from the ridges on its surface; it also arises from the infraspinatous fascia which covers it, and separates it from the Teretes major and minor. The fibers converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus. The tendon of this muscle is sometimes separated from the capsule of the shoulder-joint by a bursa, which may communicate with the joint cavity.The Teres minor(Fig. 412)is a narrow, elongated muscle, which arises from the dorsal surface of the axillary border of the scapula for the upper two-thirds of its extent, and from two aponeurotic laminæ, one of which separates it from the Infraspinatus, the other from the Teres major. Its fibers run obliquely upward and lateralward; the upper ones end in a tendon which is inserted into the lowest of the three impressions on the greater tubercle of the humerus; the lowest fibers are inserted directly into the humerus immediately below this impression. The tendon of this muscle passes across, and is united with, the posterior part of the capsule of the shoulder-joint.The Teres major(Fig. 412) is a thick but somewhat flattened muscle, which arises from the oval area on the dorsal surface of the inferior angle of the scapula, and from the fibrous septa interposed between the muscle and the Teres minor and Infraspinatus; the fibers are directed upward and lateralward, and end in a flat tendon, about 5 cm. long, which is inserted into the crest of the lesser tubercle of the humerus. The tendon, at its insertion, lies behind that of the Latissimus dorsi, from which it is separated by a bursa, the two tendons being, however, united along their lower borders for a short distance.The Subscapularis(Fig. 411) is a large triangular muscle which fills the subscapular fossa, and arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border of the bone. Some fibers arise from tendinous laminæwhich intersect the muscle and are attached to ridges on the bone; others from an aponeurosis, which separates the muscle from the Teres major and the long head ofthe Triceps brachii. The fibers pass lateralward, and, gradually converging, end in a tendon which is inserted into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. The tendon of the muscle is separated from the neck of the scapula by a large bursa, which communicates with the cavity of the shoulder-joint through an aperture in the capsule.82.ArmThe muscles of the arm are: 1 CoracobrachialisCoracobrachialis∙Origin: coracoid process of the scapula∙Insertion: medial shaft of the humerus at about its middle∙Action:1.flexes the humerus2.assists to adduct the humerus∙Blood: muscular branches of the brachial artery∙Nerve: musculocutaneous nerve, C5,6,(C7)Biceps brachii∙Origin:1.long head- supraglenoid tubercle and glenohumeral labrum2.short head- tip of the coracoid process of the scapula∙Insertion:1.radial tuberosity2.bicipital aponeurosis∙Action:1.flexes the forearm at the elbow (when supinated)2.supinates forearm from neutral3.stabilizes anterior aspect of shoulder4.flexes shoulder (weak if at all)∙Blood: muscular branches of brachial artery∙Nerve: musculocutaneous nerve, C5,6Brachialis∙Origin:1.lower 1/2 of anterior humerus2.both intermuscular septa∙Insertion:1.ulnar tuberosity2.coronoid process of ulna slightly∙Action: elbow flexion (major mover)∙Blood:1.muscular branches of brachial artery2.radial recurrent artery∙Nerve: musculocutaneous nerve, C5,6Triceps brachii∙Origin:1.long head - infraglenoid tubercle of the scapulateral head - upper half of the posterior surface of the shaft of thehumerus, and the upper part of the lateral intermuscular septum3.medial head - posterior shaft of humerus, distal to radial groove andboth the medial and lateral intermuscular septum (deep to the long &lateral heads)∙Insertion:1.posterior surface of the olecranon process of the ulna2.deep fascia of the antebrachium∙Action:1.long - adducts the arm, extends at the shoulder, and a little elbowflexionteral - extends the forearm at the elbow3.medial - extends the forearm at the elbow∙Blood:1.muscular branches of the brachial artery2.superior ulnar collateral artery3.profunda brachii artery∙Nerve: radial nerve, C6,7The Coracobrachialis(Fig. 411), the smallest of the three muscles in this region, is situated at the upper and medial part of the arm. It arises from the apex of the coracoid process, in common with the short head of the Biceps brachii, and from the intermuscular septum between the two muscles; it is inserted by means of a flat tendon into an impression at the middle of the medial surface and border of the body of the humerus between the origins of the Triceps brachii and Brachialis. It is perforated by the musculocutaneous nerve.。
