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Classic person Anatomy in Motion: The Artist"s guide to the Dynamics of figure Drawing

Chapter 5. Muscle of the Neck and Torso

The muscles of the torso are exciting on numerous levels. First, uneven the muscles of the face region, their shapes are rather recognizable on the surface. Second, few of the superficial muscle are already known by many people, despite most likely by their typical names: the shoulder muscle (trapezius), the chest or pectoral muscle (pectoralis major), the “abs” or “six-pack” (rectus abdominis), and the “flank pad” or “love handles” (external oblique). Third, the muscles of the torso execute not move just the torso (vertebral column and rib cage) but additionally the shoulder girdle, which has the scapula bones and also clavicles, as well as the upper arms (humerus bones).

You are watching: Where is your torso located on your body

There are numerous ways come categorize the torso muscles. One method is to group them by their location on the anterior, lateral, and also posterior areas of the body, yet they can likewise be share by anatomical areas (abdominal region, scapular region, pectoral region) or by your placement in relationship to the surface ar (superficial layer, intermediary layer, deep layer).

For finding out purposes, a mix of systems is used in this chapter. First, let’s look at the torso muscles according to their placement on the human body from front (anterior), earlier (posterior), and also side (lateral) views, as presented in the adhering to drawings.

MUSCLES that THE TORSO—ANTERIOR VIEW

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MUSCLES of THE TORSO—POSTERIOR VIEW

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MUSCLES the THE TORSO—LATERAL VIEW

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MUSCLES that THE TORSO suggested BY COLOR

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LEFT: Anterior view

CENTER: Posterior view

RIGHT: Lateral view

Names of Torso Muscles

The surname of torso muscles carry out clues to their location, shape, size, or the direction of their muscle fibers.

·Abdominispertains come the abdominal muscle region.

·Pectoralispertains come the chest region.

·Anteriormeans “front.”

·Dorsimeans “back.”

·Spinalisorspinatusindicates a ar on or close to a sharp bony projection, or spine.

·Externalmeans “outer.”

·Internalmeans “inner.”

·Majormeans “larger.”

·Minormeans “smaller.”

·Rectusmeans “straight.”

·Obliquemeans “slanted” or “diagonal.”

Muscles of the Neck

Before relocating on to the individual muscle teams of the torso, let’s pause for a moment to look in ~ the muscles of the neck—the transitional area in between the head and torso. We already began doing therefore in the previous chapter, where I extended the suprahyoid muscles (this page) and the platysma (this page), which play roles in moving the jaw and in facial expressions. Here, we’ll emphasis briefly top top the sternocleidomastoid (SCM) and also the infrahyoid muscle group. The significant muscle of the back of the neck, the trapezius, is affiliated in movements of the scapula and also is dealt with in the next section, ~ above the muscles of the thorax.

Thesternocleidomastoid(pron., STIR-no-KLIE-doe-MASS-toid) is a straplike muscle positioned top top either next of the neck. This muscle begins at two different locations, one ~ above the sternum (sternal portion) and the various other on the clavicle (clavicular portion). The muscle fibers at some point merge right into one shape, i m sorry inserts right into themastoid process(a tiny protrusion the bone on the skull behind the ear) and also along a small ridge called thesuperior nuchal heat of the occipital bone.

The sternocleidomastoid muscle help bend and twist the head and also neck in various directions, including flexion (bending the head forward), lateral flexion (bending the head sideways), and also rotation (twisting the head left or right).

Theanterior triangle the the neck regionis located between the inside borders of the sternocleidomastoid muscles, the top section of the sternum (manubrium), the hyoid bone, and also the lower border that the digastric muscle (posterior belly). It contains several necessary structures, including the larynx (voice box), trachea (windpipe), and also thyroid cartilage and gland. It is additionally the ar of four straplike muscles jointly referred to together theinfrahyoid muscles,which means the musclesbelowthe hyoid bone. The four muscles space thesuperior belly of the omohyoid,thesternohyoid,thethyrohyoid,and thesternothyroid.

The infrahyoid muscles within the anterior triangle that the neck are rather hard to check out on the surface form, but on some occasions, relying on the position of the neck, one or 2 muscles might be detected, as once the head bends back and the sternohyoid muscles create subtle upright ridgelike forms on either next of the thyroid cartilage. The following illustration onthis pageshows the muscles of the neck and shoulder region. (For conversation of the muscle of the suprahyoid group—digastric, mylohyoid, and stylohyoid—seethis page.)

MUSCLES of THE NECK and also SHOULDER REGION

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Anterior watch of head tilting back

Muscles that the Thorax

Thethoracic musclesattach top top the anterior and also lateral areas of the thorax, or rib cage. They room the pectoralis major, the pectoralis minor, and also the serratus anterior. The pectoralis significant muscle helps relocate the humerus, and also the pectoralis minor and the serratus anterior muscles assist move the scapula bone.

THORACIC MUSCLES

The torso is separated in half to show the 2 layers of muscle in this region. The muscle on the left side space the superficial muscle (close come the surface), and also the muscle on the ideal are positioned in ~ the superficial muscles.

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Anterior view

Thepectoralis major(pron., PECK-tor-AL-liss MAY-jur) is a large, fan-shaped muscle that occupies the anterior region of the rib cage on either next of the sternum. This muscle has actually three portions:clavicular, sternal,andabdominal.The pectoralis major forms the anterior wall of the axillary region, or the armpit (seethis page), i beg your pardon becomes obvious when the top arm is positioned far from the torso. The breast form, a combination of glandular and also fatty organization forms, is attached to the fascia (a sheathing layer) the is situated over the pectoralis major muscle.

The clavicular part begins top top the clavicle; the sternal portion begins follow me the outer side of the sternum; and the abdominal portion begins on a tiny section of the abdominal sheath. The muscle yarn pull across the rib cage and converge to connect on the humerus (upper eight bone). Once the top arm is lifted away from the torso, the insertion of this muscle is seen more clearly.

The pectoralis major, shown in the next illustration in both anterior and lateral views, moves the humerus in miscellaneous ways relying on which portion is contracting and which various other muscles room assisting. The key actions are relocating the humerus in a forward direction (flexion), moving the humerus indigenous an overhead position and also returning it to the next of the torso (adduction), and also rotating the humerus in an inward direction (medial rotation).

PECTORALIS MAJOR

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Torso, anterior (left) and also lateral (right) views

The complying with life study,Male number Holding a Staff,focuses top top the pectoral area. Through the arms positioned away from the torso, the is basic to see just how the pectoralis major inserts into the humerus that the top arm. The thick outer edge is the anterior wall of the axillary (armpit) region. The accompanying diagram reveals the action of the muscle in this pose.

MALE figure HOLDING A STAFF

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Graphite pencil and watercolor pencil on light toned paper.

MUSCLE DIAGRAM

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The next life studySeated woman Figure,shows the upper part of the pectoralis major positioned flat against the rib cage, through very little thickness. The soft-tissue creates of the breasts, consisting of glandular tissue (mammary glands) and fatty tissue, are anchored ~ above the fascia sheathing that covers the pectoralis muscle. As the skin pulls end these creates (muscle and also soft tissue) it create a soft shift on the surface from the loved one flatness of the upper rib cage come the affluent spherical shapes of the breasts.

SEATED woman FIGURE

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Sanguine and brown pastel pencils and white chalk top top toned paper.

Thepectoralis minor(pron., PECK-tor-AL-liss MY-nor) is composed of three muscle strips positioned beneath the pectoralis major. The is generally not detectible on the surface form. Each muscle strip of the pectoralis minor starts on a different rib (ribs 3 through 5). The muscle climate inserts into the coracoid process (a small, beaklike bony protrusion) of the scapula. The pectoralis boy helps lower the shoulder tongue in the activity of depression of the scapula and moves the scapula in a front direction in the protraction that the scapula.

Theserratus anterior(pron., sir-RAY-tus an-TEER-ee-or, sir-RAH-tus an-TEER-ee-or, or SIR-ah-tus an-TEER-ee-or) is a fan-shaped muscle consists of eight or nine separate muscle digitations (finger-like shapes) located on the lateral an ar (outer side) of the rib cage. Every of these elongated muscle strips attaches top top a separate rib, start with the first rib, and wraps approximately the side of the rib cage come insert into the medial (inner) border that the scapula. The serratus anterior is mostly concealed by the pectoralis significant and the latissimus dorsi muscles, but the lower three or 4 digitations deserve to be clearly shows on the surface, appearing as small, riblike forms between the outer edge that the pectoralis significant and the external edge of the latissimus dorsi.

The main actions of the serratus anterior are the protraction and upward rotation that the scapula. Protraction the the scapula is the action of relocating the scapula in a front direction and occurs once the eight is reaching forward in former of the torso, as displayed in the following drawing. Increase rotation is the tilting the scapula in a increase direction and occurs when the eight is elevated overhead.

SERRATUS ANTERIOR, with DELTOID MUSCLE

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Lateral view of torso with humerus lifted in a front direction

The life studyMale number Lifting His ideal Arm, next View,right, mirrors a guy raising his eight to reveal the muscles more clearly. Between the rich external edge of the latissimus dorsi and pectoralis significant appear some tiny riblike develops that are the partially exposed shapes of the serratus anterior.

MALE number LIFTING HIS best ARM—SIDE VIEW

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Graphite pencil, watercolor wash, and white chalk on toned paper.

The abdominal Muscle Group

Occupying the anterior and lateral areas of the abdominal area the the torso space three great of muscles: Thesuperficial muscle layercontains the exterior oblique and also rectus abdominis—the two abdominal muscle muscles viewed on the surface ar form. Theintermediate layercontains the interior oblique, and also thedeep layercontains the transversus abdominis. The ab muscle team helps relocate the vertebral column and also rib cage in the plot of forward bending (flexion), side bending (lateral flexion) and rotation, and causing the compression the the abdominal muscle wall. Muscles belonging to each of the layers are shown in the complying with drawing.

ABDOMINAL MUSCLE GROUP

Anterior and lateral areas of the torso

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LEFT:Rectus abdominis (superficial layer)

RIGHT:External tilt (superficial layer)

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LEFT:Internal oblique (intermediate layer)

RIGHT:Transversus abdominis (deep layer)

Three ab muscles—the transversus abdominis, internal oblique, and external oblique—are layered atop each various other on the lateral region of the lower torso; their muscle fibers run in various directions, producing a twisting or swiveling activity of the torso when these muscles contract. Each of this muscles has its own huge tendinous sheathing that continues throughout the abdomen to attach into the linea alba—a fibrous vertical type that attaches indigenous the base of the sternum come the pubic bone the the pelvis. The layered sheathings act together a fibrous sleeve in i m sorry the rectus abdominis muscle (located in the anterior region of the reduced torso) is encased. As soon as the anterior (front) great of this sheath is removed, the rectus abdominis muscle is exposed to disclose its eight muscle segments.

The various layers the sheathing the the abdomen have different names, i beg your pardon can reason confusion as soon as studying this region. Including to the potential difficulty, the anterior class (positioned end the rectus abdominis muscle) is referred to by number of names: theexternal oblique aponeurosis,or therectus sheath (anterior layer),or sometimes theabdominal sheathing.The sheathing the the interior oblique is usually called theinternal slope aponeurosis,and the sheathing that the tranversus abdominis is called therectus sheath (posterior layer),because that is positionedbeneaththe rectus abdominis muscle.

Therectus abdominis(pron., RECK-tuss ab-DOM-ih-niss) muscle rectal the front part of the torso in the abdomen region. The muscle is separated by a vertical fibrous line dubbed thelinea alba(“white line”) and three horizontal fibrous lines referred to as thetransverselines. The rectus abdominis is commonly known as the “six-pack,” because the muscle is split into six sections above the navel, which appear as six little forms top top the surface ar of some muscularly defined torsos. Listed below the navel, the muscle is divided into second two segments (more on some individuals), yet a class of fat tissue generally softens the lower two segments into one shape. Differences between the rectus abdominis together it shows up on males and also females space examined in the sidebar onthis page.

The rectus abdominis begins on the pubic bone and also pulls straight up to connect into the xiphoid process of the sternum and also the costal cartilages that the fifth, sixth, and seventh ribs. The muscle helps bend the torso forward in the movement well-known as theflexion that the vertebral column.It also helps raise the human body from a supine position to one upright sitting position.

Thepyramidalis(pron., purr-RAM-ah-DAY-liss or PEER-ah-mah-DALL-liss) is a very little triangular muscle located at the base of the rectus abdominis. That is tough to finding on the surface type because the muscle fibers blend through those the the rectus abdominis. The muscle starts on the pubic symphysis the the pelvis and inserts right into the lower section of the linea alba. The pyramidalis go not aid move any kind of bones. That main function is to help tense the linea alba. Both the rectus abdominis and also the pyramidalis are presented in the adhering to drawing.

RECTUS ABDOMINIS, with PYRAMIDALIS

Superficial layer of ab muscle group, anterior region of torso

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Torso, anterior (left) and lateral (right) views

Theexternal oblique(pron., ex-STER-nal oh-BLEEK) is situated on the lateral (side) part of the torso. The muscle is composed of eight elongated muscle digitations and also is separated into 2 portions: thethoracic portionand theabdominal portion,also dubbed theflank pad.The thoracic section hugs the rib cage prefer a girdle and is hard to detect on the surface other than in muscularly characterized torsos. The individual muscle strips that the thoracic part begin on the ribs and appear to interweave v the muscle digitations of the serratus anterior. The flank pad part is much more noticeable together a bulbous shape beginning below the waistline. At the bottom portion, its muscle yarn anchor along the upper rim of the pelvis (iliac crest), slightly cascading end it close to the ASIS of the pelvis. While this is a muscle form, that is usually intensified with a class of fatty tissue, providing it a rounded, an ext prominent shape. Artists use this form as vital landmark in torso studies.

EXTERNAL OBLIQUE

Superficial class of abdominal muscle muscle group, lateral region of torso

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Torso, anterior (left) and also lateral (right) views

The outside oblique begins on the reduced eight ribs (ribs 5 v 12) and inserts into the iliac stakes of the pelvis, the inguinal ligament, and the aponeurosis the the exterior oblique and linea alba. As soon as the external oblique contracts, that helps bending the torso in a forward direction (flexion) and also sideways (lateral flexion). It also helps move the torso in a twisting action (rotation). The flank pad section can large or compress, particularly when the torso bends at the side in a dynamic way.

In the life studyMale figure with Left Hand on Hip,we view the abdominal an ar (rectus abdominis and also the exterior oblique), along with the pectoralis major of the thoracic group. The diagram accompanying the drawing reveals the plot of the muscle in this pose.

MALE number WITH LEFT HAND on HIP

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Graphite pencil, brown ink, watercolor wash, and also white chalk top top toned paper.

MUSCLE DIAGRAM

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Rectus Abdominis—Male matches Female

The illustrations here present idealized versions of male and also female torsos. The male torso mirrors the standard muscle divisions (“six-pack”) of the rectus abdominis; the woman torso, commonly having much more subcutaneous tissue, is softer in appearance, through an all at once shape comparable to that of a violin. There are, however, numerous variations among real people, male and also female. Women that do extensive weight training can construct six-packs, if the rectus abdominis in men deserve to be obscured through excess fat tissue, developing what is colloquially known as a beer belly.

DIFFERENCES IN THE ab REGION—MALE and FEMALE

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LEFT: masculine torso, anterior viewMuscle forms are much more apparent top top the surface

RIGHT: mrs torso, anterior viewMuscles room covered with a thicker great of subcutaneous tissue, softening the surface ar form

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LEFT: A muscular masculine abdomen is similar to a six-pack.

RIGHT: The woman abdomen is typically softer and also violin-shaped.

Muscles the the Back

The muscles of the ago move the shoulder blade (scapula), top arm (humerus), and earlier (vertebral column). They attach along the vertebral column and are split into 3 muscle layers: Thesuperficial layercontains the trapezius and the latissimus dorsi. Theintermediate layercontains the rhomboid major, rhomboid minor, and levator scapulae. Thedeep layercontains the sacrospinalis. Muscle of the superficial and intermediate layers are shown in the drawing onthis page; the muscles of the scapula and also the deltoid muscle are had here however will be introduced separately, later in the chapter.

The Superficial Muscle Layer

The muscles of the superficial layer of the earlier move the shoulder tongue (scapula) and upper arm (humerus). The two big main muscle of this layer space the trapezius and also the latissimus dorsi.

Thetrapezius(pron., traa-PEA-zee-us) is a trapezoid-shaped muscle positioned ~ above the upper back. Its distinctive shape, presented in the following drawing helps produce the shoulder forms, the back of the neck, and also the muscle forms of the top back. Its fibers divide into three portions: thesuperior (upper) portion, transverse (middle) portion,andinferior (lower) portion.The muscle originates in ~ the base of the cranium (occipital protuberance), nuchal ligament, C7 (seventh vertebra), and also all follow me the thoracic vertebrae. It inserts right into the outer part of the clavicle, the spine that the scapula, and the acromion of the scapula.

TRAPEZIUS

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Posterior view

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Anterior view

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Lateral view

Each portion of the trapezius helps move the scapula in a different way. These actions encompass lifting the scapula in an increase direction (elevation), tilting the scapula (upward rotation), and also moving the scapula back (retraction/adduction). The upper portion of the muscle additionally helps bend the neck and also head backward (extension of the neck).

Thelatissimus dorsi(pron., lah-TISS-ih-mus DOR-see or lah-TISS-ih-muss DOR-sigh), displayed in the adhering to drawing, is a big triangular muscle the occupies many of the lower back region. Top top athletic numbers (particularly body builders and also swimmers) this muscle offers the earlier of the torso a V-shaped appearance. In a next view, once the eight is pulled forward, the outer edge the the muscle is usually viewed as a special curve obliquely cross the torso and also heading straight into the armpit the the upper arm, developing the posterior wall surface of the axillar region.

MUSCLES the THE BACK

Superficial and also intermediate muscle layers

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LATISSIMUS DORSI

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LEFT: Posterior view

RIGHT: Lateral view

The muscle begins on the thoracic vertebrae (T7–T12) and lumbar vertebrae (L1–L5), the ribs (ribs 10 with 12), the iliac stakes of the pelvis, and the sacrum. That inserts right into the humerus (upper eight bone). The latissimus dorsi assists in the plot of relocating the humerus indigenous a front position ago to the side of the torso (extension), moving the humerus indigenous an overhead position and returning it come the side of the torso (adduction), and rotating the humerus in an inward direction (medial rotation).

In the life studyFemale number in a back View, Leaning Slightly,the ago muscles appear really soft since of a padded layer of superficial fatty tissue. Once approaching a examine of a figure with a same amount of fat tissue, remain aware of the bony framework beneath. Try to find the places of the vertebral column, sacrum, and also scapula bones, due to the fact that they aid divide the back of the torso into workable components and also serve as visual landmarks for the placement of muscle develops such as the trapezius, latissimus dorsi, and also gluteal group. When these room placed, the fatty tissue can be emphasized to create softer transitions ~ above the surface form.

FEMALE figure IN A ago VIEW, LEANING SLIGHTLY

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Graphite pencil, sanguine colored pencil, and white chalk top top toned paper.

Now, to compare the life studyMale number in a Three-quarter earlier View,with the examine of the female figure. In this check out of a male number with one eight up and also one arm on the hip, over there is a significant number of plainly defined anatomical shapes, huge and small. To stop confusion when drawing such a muscular figure, very first set up the general structures lightly—the forms of the rib cage and pelvis, head and neck, and arm structures, in addition to the place of the vertebral column, sacrum, and also the scapula bones. Then locate the huge muscle shapes of the trapezius, latissimus dorsi, and also the gluteal group. Medium-size creates such together the deltoid, the columnlike develops of the sacrospinalis, the flank pad that the exterior oblique, and the scapula muscles can be located next. Climate go ago to each larger muscle and continue to failure the miscellaneous subforms you might see. Including the tones and lights as you go helps store the muscles connected and produces a sense of continuity.

MALE figure IN A THREE-QUARTER earlier VIEW

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Graphite pencil and white chalk top top toned paper.

In poses such as this, you can see exactly how the muscles change shape depending on the action of the arms and the location of the rib cage and pelvis. The diagram accompanying the drawing further reveals the action of the muscles in this pose.

MUSCLE DIAGRAM

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The intermediate Muscle Layer

The muscles of the intermediate muscle class of the earlier are positioned beneath the trapezius and also the latissimus dorsi. They encompass the rhomboid major, rhomboid minor, and levator scapulae and also are responsible because that helping to move the shoulder tongue (scapula) and the top arm (humerus).

The rhomboid minor and rhomboid significant muscles attach between the vertebral column and also the inside (medial) border the the scapula. Both room positioned beneath the superficial-layer trapezius muscle. The termrhomboidmeans “diamond shaped,” and also together the rhomboids kind a pair that parallelograms, one on either side of the vertebral column.

Therhomboid minorhas a four-sided form very similar to the geometric figure referred to as a rhombus. The smaller of the two rhomboid muscles, it begins on the seventh vertebra the the neck (C7) and the an initial thoracic vertebra that the rib cage (T1) and inserts right into the vertebral (or medial) border of the scapula.

The largerrhomboid majorbegins on the thoracic vertebrae (T2–T5) and also inserts right into the vertebral (or medial) border of the scapula. Only a small part of the rhomboid major is ever visible on the surface, due to the fact that most the the muscle is spanned by the trapezius. That is occasionally confirmed by a little triangular bulge or depression between the external border the the scapula, the outer lower border of the trapezius, and also the upper border that the latissimus dorsi.

Both the rhomboid major and young muscles participate in the actions of pulling the scapula towards the vertebral column (protraction/adduction), lifting the scapula in an increase direction (elevation), and also tilting the scapula is a downward direction (downward rotation).

Thelevator scapulae(ley-VAY-tor SCAP-yoo-lee) has 4 individual muscle strips that merge right into one muscle mass. The is positioned beneath the upper component of the trapezius muscle. The muscle begins on the very first four cervical (neck) vertebrae and also inserts right into the external upper leaf of the scapula. The levator scapulae participates in relocating the scapula in an upward direction (elevation) and also tilting the scapula in a downward direction (downward rotation).

The Deep Muscle Layer

Within the deep muscle great of the back is thesacrospinalis(pron., SAY-kro-spih-NAL-iss or SAY-kro-spy-NAY-liss), a large, columnlike muscle that divides right into multiple segments. That is positioned beneath the rhomboid muscle of the intermediate layer and also the trapezius and latissimus dorsi the the superficial layer. The drawing listed below shows the position of the sacrospinalis relative to the muscle of the superficial layer.

SUPERFICIAL and also DEEP MUSCLE great OF THE BACK

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Left side: Superficial muscle layer

Right side: Deep muscle layer

The sacrospinalis, likewise known as theerector spinae,is one incredibly complex muscle. The is separated into 3 main groups on each side the the vertebral column: theiliocostalis group(outer/lateral portion), thelongissimus group(intermediate/middle portion), and thespinalis group(medial/inner portion). Within every of these groups are further subdivisions. It is daunting to view all these subdivisions on the surface, despite on muscular body the combination of the many components of this muscle creates 2 large, columnlike forms on either side of the vertebral column, beneath the latissimus dorsi and trapezius. On bodies with much less muscle definition, the lower portion of this muscle appears as two slender cylindrical creates positioned side by next directly above the sacrum.

The muscle originates in ~ the sacrum, all follow me the lumbar vertebrae (L1–L5), and at the last two thoracic vertebrae (T11–T12). It inserts into the angle of the ribs, follow me the cervical and also thoracic vertebrae, and eventually right into the mastoid process of the cranium. The sacrospinalis assists in the actions of moving the vertebral tower from a forward-bending position ago to an upright place (extension) and also of bending the torso earlier (hyperextension). It also assists in bending the vertebral column and also rib cage sideways (lateral flexion) and helps preserve the vertebral obelisk in one upright posture when there is no physical activity (isometric contraction).

In the life studyMale figure in a Boxing Pose,several muscle of the figure’s back are an extremely prominent since of their contracted state. The scapular muscle group, sacrospinalis, trapezius, and also deltoid are especially noticeable, and the exterior oblique, latissimus dorsi, as well as the triceps brachii the the best arm are plainly visible, together well. The diagram accompanying the drawing further discover the action of the muscles in this pose.

MALE figure IN A BOXING POSE

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Graphite pencil and white chalk ~ above toned paper.

MUSCLE DIAGRAM

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The Scapular Muscle Group

The muscles of the scapular group are thesupraspinatus, subscapularis, infraspinatus, teres major,andteres minor.The supraspinatus is positioned on the upper part of the scapula and also is fully covered by component of the trapezius muscle. The subscapularis is attached under the scapula and can never be viewed on the surface. As such only the infraspinatus, teres major, and teres minor are displayed in the complying with drawing.

SCAPULAR MUSCLE GROUP

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Torso, posterior view

All these muscles originate on the scapula and insert right into the humerus bone that the upper arm. The scapular muscle group does not move the scapula, also though the muscles attach directly top top it. Their duty is to move the humerus in assorted directions. Actions include moving the humerus far from the next of the torso (abduction), rotating the humerus in an outward direction (lateral rotation), rotating the humerus in an inward direction (medial rotation), returning the humerus indigenous a outstretched side place to the side of the torso (adduction), and also returning the humerus from a front position back to the side of the torso (extension). Several motions of the upper arm, however, cannot be accomplished without the scapula additionally moving. This is made feasible by one more group the muscles, consisting of the trapezius, rhomboid significant and minor, levator scapulae, and pectoralis minor.

Scapular Muscle Group

MUSCLE

PRONUNCIATION

supraspinatus

SOO-prah-spih-NAH-tuss orSOO-prah-spy-NAY-tuss

infraspinatus

IN-frah-spih-NAH-tuss orIN-fra-spy-NAY-tuss

teres major

teh-REEZ MAY-jur

teres minor

teh-REEZ MY-nor

subscapularis

SUB-scap-yoo-LAR-iss

The Deltoid

Thedeltoid(pron., DELL-toyd) is the triangular muscle the the shoulder and also upper arm. A transitional muscle linking the shoulder girdle the the torso and also the upper arm, the deltoid deserve to be stated to belonging both come the torso muscles and to the top arm muscles.

The deltoid’s shape is similar to the of a sporting activities shoulder pad. Neighboring the fragile shoulder share (glenohumeral joint) that the top arm and also scapula, the muscle appears as a triangular shape in former views and also as an turning back teardrop or oval form in next views the the arm.

The deltoid has three portions: theanterior portion(clavicular portion), which starts on the clavicle; thelateral portion(acromial portion), which starts on the acromion procedure of the scapula; and theposterior portion(spinal portion), which starts along the spine of the scapula. The muscle yarn converge to insert into a small attachment site about halfway under the outer component of the humerus. As soon as the arms space lifted overhead, from a back view the is sometimes possible to see the separation of these portions approximately the clavicle and also the acromion process of the scapula.

The deltoid moves the humerus to various positions relying on which section is contracting and which other muscles space assisting. Actions encompass helping relocate the humerus in a front direction (flexion), returning the humerus from a flexed position earlier to the next of the torso (extension), relocating the humerus farther back (hyperextension), rotating the humerus in an inward direction (medial rotation), rotating the humerus in an external direction (lateral rotation), and moving the humerus far from the next of the torso (abduction).

DELTOID

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LEFT: Anterior view

RIGHT: Posterior view

The Axilla

Theaxilla,oraxillary region,is frequently referred to as thearmpit, pit that the arm, or hole of the arm.It is a junction of various muscles, softened with connective tissue and also fatty tissue (fat pads). The skin pulls throughout the hollow created by the intersection the muscles and also the border of the muscles themselves. The axilla alters shape and size relying on the place of the arm in relation to the torso. As soon as the eight is pulled away from the torso, the fatty organization within the axilla temporary recedes and also a deep hollow occurs in this an ar (hence the namepit the the arm), however when the arm is raised overhead, the axilla appears as a soft mound.

There are several materials of the axillar region, referred to as “walls” the the axilla: theanterior wall surface of the axilla,theposterior wall of the axilla,themedial wall surface of the axilla,and thelateral wall of the axilla.There is additionally thefloor the the axilla.

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The anterior wall is created by the pectoralis major and pectoralis minor muscles, and also is viewed on the surface quite plainly as a strong, muscular form moving from the rib cage right into the upper arm. The upper part of the coracobrachialis muscle is covert by the anterior wall when the eight is at the side of the torso; as soon as the arm is increased overhead, however, it shows up as a little elongated kind located next to the upper part of the biceps; this area is the lateral wall. The posterior wall surface is formed by the teres major and latissimus dorsi muscles, together with the subscapularis muscle beneath. The medial wall consists the the upper 4 ribs and the upper 4 digitations the the serratus anterior muscle. The floor the the axilla consists of the axillar fascia and the skin stretching between the anterior and posterior walls. As soon as the arms space pulled increase or far from the torso, you have the right to usually detect just the anterior and also posterior walls, and also the floor that the axilla. The coracobrachialis and also a few of the fingerlike digitations the the serratus anterior located in between the an ext obvious anterior and also posterior walls may also be recognize on the surface.