Lesson 2 Basic Ecorche


-Serratus anterior

-Spinal muscles group:

  1.  Lumbar spine columns

  2. Lateral Erector spinae

-Rectus Abdominis

-External Oblique


Serratus anterior

-Fleshy attachments to ribcage create the characteristic profile (the “serrated lumps” or “fingers”) standing out from ribcage

-The “serrations” of this muscle where it attaches to the ribs follow an arc down and back from approximately the position of the nipple on male

-It attaches to the first 8 OR 9 ribs (ie there is variation in the human population), with only the bottom 4 or five visible under the bottom border of the Pectoralis Major 

-The angle of the “fingers” of the Serratus Anterior, in most positions where they are visible will be steeper than the angle of the rib that each one originates on.

- To sculpt:

1. mark with a pencil the arc of the join of the ribs to the costal cartilage - this may be visible in the cast model to some extent as little bumps, or estimate by viewing the front and side profile of the model at right.

2.mark the arc of the the tips of the serratus muscles where they attach onto ribs 1-9,  Notice how the arc follows the approximately the first line you drew, but the distance between the lines widens as you move down (superior to inferior direction)

3. begin adding the fingers one at a time from the LOWEST rib first. Be careful to not make them too thick as they project off the surface of the model.  Only the bottom 4 or 5 will be visible, but you can add the others to learn the muscle

4 turn to the posterior of the figure.  The serratus anterior muscle inserts onto the inside of the scapula as described below.  Again this will be covered but you can put this is in to learn the muscle



-First 9 ribs


-Costal aspect  of medial margin of scapula (ie the inside of the edge closest to the vertebral column, wrapping around underneath the scapula - "costal aspect" means the side closest to the ribs )

NB: As is standard for Anatomy-speak, the "origin" is considered the end closest to the centre of the figure or the torso.  The "insertion" is generally the end that attaches onto the limb, in this case moving or stabilising the shoulder relative to the torso (relative because the limb could stay still and the shoulder move, or the limb should stay still and the torso move or both.

Colour on your



The Spinal Muscles Group:


The muscles of the spine are a complex collection of muscles.  We will leave aside this detail and consider the main forms they contribute to:

1. they extend the “Inner neck volume” (that you have added already) down either side of the vertebral column

2. the columns of the lumbar spine

3. the thickening of the lumbar area to the sides of this.   

Later, these muscles will be covered in the lower region by parts of the the Latissimus dorsi, and the Thoraco-lumbar fascia that anchors the former to the vertebral column and the pelvis.  At the the top of the back, this group will be covered by the Trapezius and other muscles.  However they are important for setting up the form of the back.

Also, it is worth noting that the deepest part of the groove of the spine is located just below the lowest part of the ribcage, and the spinal muscles group contribute to this deepening.



We will simplify these muscles into two groups: 


1: Those that form the columns to either side of the lumbar spine (called in this course the “Lumbar spine columns”)

2. Those that fill out the volume to the sides of the columns (called below the “Lateral Erector spinae”

Spinal muscles group 1:

The Lumbar Spine Columns

-This volume will include both the Multifidus and the Longissimus thoracis, and runs from the sacrum to the top of the cervical spine, (ie the whole length of the vertebral column).

-It is an important surface form where it thickens out in the lumbar region, becoming more cylindrical, and in a neutral pose is the major contributor to the volume of soft tissue that projects beyond these vertebral spines. 

-In Lesson one, you put in the inner neck volume that included the cervical region of this group, so now you only need to worry about extending the volume downwards.

Origins and Insertions:

Multiple points along full length of the vertebral column as well as the medial (inside) surfaces of the posterior superior illiac spines, just near the join of the sacrum to each iliac crest.

Colour on your model:


Spinal muscles group 2:

The Lateral Erector spinae

- The Erector spinae group consists of the various Iliocostalis, Longissimus, and Spinalis muscles. 

- Covers much of the Multifidus

-We will conceive of this complex group of muscles as a broad strap-like unit that in the thoracic region is wider and flatter, laying in the groove of the ribcage on either side of the spines of the thoracic vertebrae - be careful to not make this region too deep.

-In Lesson one, you put in the inner neck volume that included the cervical region of this group of muscles, so now you only need to worry about extending the volume downwards.

-The group is covered in the ribcage and lumbar spine areas by Thoraco-Lumbar Fascia, which can for our purposes in artistic anatomy be thought of as a very broad tendon connecting the Latissimus Dorsi to the lumbar spine (This will be added later)

- The principle surface visible form that results from this muscle group is where the Iliocostalis lumborum extends the volume of the ribcage downwards on either side of the Multifidus, contrtibuting to the diagonal grooves that run down and out from the lowest thoracic spine, on either side of the Lumbar spine columns group


Origin and insertions:  This group attaches to points all along the vertebral column, ribcage and pelvis.


Colour on your model:


Rectus Abdominis

-The “six pack muscles” which actually has 8 bodies not 6

- Notice how in this particular figure with an open, slightly arched torso, reveals the profile of the ribcage arch pushing through the rectus abdominis.

- Notice how the lower muscle bodies of the Rectus abdominis, below the navel (belly button) bulge out slightly more than those above.


Bending forward actions: flexion of the torso, bringing the front of the ribcage closer to front of the pelvis, as in a sit-up


Pubis of pelvis


Cartilage of ribs 5 -7 , Xiphoid process (tip of sternum)

Colour on model: Red

External oblique

-This muscle interlocks with the Serratus anterior (on each of the 4 or 5 ribs where it is visible) and borders with the Latissimus dorsi. It covers the broad tapering sides of the abdomen down to the approximately the front half of the iliac crests

-It covers the top edge of the iliac crest, unless contracted and thereby lifted out of the way

-The characteristic shadow under the base of this muscle (most obvious on a lean athletic model) can be used to find the angle of the hips

-The oblique is a relatively thin sheet of muscle.  There is a characteristic hollow on either side of the rectus abdominus under the bottom edge of the ridcage arch.  

-The angle of the fibres of the oblique is steeper than the angle of those of the Serratus Anterior, fanning out from nearly horizontal to nearly the angle of the iliac crest sloping forward.

-We may see the direction of muscle fibres across the oblique if the muscle is contacted in a twist or sit up, on a lean model.

-But when the side of the body is stretched and the oblique is not contracted it is possible to see the profiles of the ribs underneath in the superior region



-Flexion of the trunk, ie bending forward motions 

-Sometimes called an “opposite side rotator” because the right side engages when twisting to the left and vice versa.  In these diagrams, and your model, the figure is twisting the upper body towards the left, which means the right side External oblique is engaged and lfted above the iliac crest, whereas the left side is relaxed and dips below the iliac crest.



The lower eight ribs, near the origin of the Serratus anterior, with which its bodies interlock



-Inguinal ligament

-anterior (front) half of the iliac crest

-connective tissue of the abdominal region, towards the midline


Colour on your model:


A simplified torso 

This model shows the main masses that we observe articulating in the abdomen near the waist - ribcage, Rectus abdominis, external oblique.  See below for classical examples and photo reference that shows these forms


-This muscle elegantly sweeps from the pit of the neck to the base the skull behind the ears

-The tendons of this muscle where it attaches to the top end of the sternum are often visible projecting more steeply than the angled “shelf” of the shoulders (the angle from the clavicle to the trapezius)


The top surface of the Manubrium (top of sternum) and medial Clavicle    


The skull behind the jaw - Mastoid bone and attachments just behind this    

Colour on your model:


In Vivo: Surface forms of the anterior abdomen in different positions

Neutral position

Arched position

Contra posto and Isolation




 Examples from Classical Art

3D Scans of classical sculptures from Sketchfab.com