Cat Dissection - Muscle Checklist

Masseter Muscle

Origin: Zygomatic arch (cheekbone)

Insertion: Mandible (lower jaw): specifically, the lateral surface of the ramus and coronoid process.

Action: Elevates the mandible forcefully, thereby closing the jaw to facilitate chewing (mastication). It also plays a minor role in protracting the mandible.

Suprahyoid Muscles

Function: This group of four muscles (Digastric, Stylohyoid, Mylohyoid, Geniohyoid) is located superior to the hyoid bone. Their primary functions include elevating the hyoid bone, elevating the floor of the mouth, and depressing the mandible (opening the mouth). They play crucial roles in the initial stages of swallowing and in modifying the oral cavity for speech and mastication.

Geniohyoid Muscle

Origin: Mental spine on the posterior surface of the mandible (lower jaw, near the chin).

Insertion: Anterior surface of the body of the hyoid bone.

Action: Elevates and draws the hyoid bone anteriorly (forward), which can also help depress the mandible when the hyoid is fixed, aiding in opening the mouth.

Hyoglossus Muscle

Origin: Body and greater horn of the hyoid bone.

Insertion: Side of the tongue (an extrinsic muscle of the tongue).

Action: Retracts and depresses the tongue, making it flatter. This action is important during swallowing and speaking.

Digastric Muscle

Origin: Anterior belly from the digastric fossa on the inner surface of the mandible; Posterior belly from the mastoid notch of the temporal bone.

Insertion: Both bellies insert into the intermediate tendon, which is attached to the hyoid bone.

Action: Elevates the hyoid bone and depresses the mandible (opens the mouth) when the hyoid bone is fixed. It assists in swallowing and mastication.

Mylohyoid Muscle

Origin: Mylohyoid line on the inner surface of the mandible (lower jaw).

Insertion: Median fibrous raphe and anterior surface of the hyoid bone.

Action: Forms the muscular floor of the mouth. It elevates the hyoid bone, elevates the floor of the mouth, and elevates the tongue. This action is critical for swallowing (raising the tongue and pushing food to the pharynx), speaking, and supporting the mandible.

Stylohyoid Muscle

Origin: Styloid process of the temporal bone (a slender projection from the skull).

Insertion: Body of the hyoid bone.

Action: Elevates and draws the hyoid bone posteriorly (backward) and superiorly (upward), assisting in the initial stages of swallowing.

Infrahyoid Muscles

Function: This group of muscles includes the Sternohyoid, Omohyoid, Sternothyroid, and Thyrohyoid. Their primary role is to depress and stabilize the hyoid bone and larynx during actions such as swallowing, speaking, and chewing. They act to return the hyoid bone and larynx to their resting positions after elevation.

Sternohyoid Muscle

Origin: Posterior surface of the manubrium and medial end of the clavicle.

Insertion: Inferior border of the body of the hyoid bone.

Action: Depresses and stabilizes the hyoid bone, particularly after it has been elevated during swallowing or speaking.

Sternothyroid Muscle

Origin: Posterior surface of the manubrium (sternum).

Insertion: Oblique line on the lamina of the thyroid cartilage.

Action: Depresses the thyroid cartilage (larynx) and also helps to depress the hyoid bone indirectly by acting on the larynx. It is crucial for vocalization and swallowing.

Thyrohyoid Muscle

Origin: Oblique line on the lamina of the thyroid cartilage.

Insertion: Greater horn and adjacent body of the hyoid bone.

Action: Depresses the hyoid bone and elevates the larynx. This muscle helps in controlling the position of the larynx during speech and swallowing.

Cricothyroid Muscle

Origin: Anterior and lateral parts of the arch of the cricoid cartilage.

Insertion: Inferior horn and lower lamina of the thyroid cartilage.

Action: Tenses and elongates the vocal cords by drawing the thyroid cartilage forward and downward relative to the cricoid cartilage. This action is essential for increasing the pitch of the voice.

Sternocleidomastoid Muscle (mammals/humans)

Origin: Manubrium (sternal head) and clavicle (clavicular head).

Insertion: Mastoid process of the temporal bone and lateral half of the superior nuchal line of the occipital bone.

Action: Bilateral contraction flexes the head and neck (brings head towards chest) and can extend the head at the atlanto-occipital joint. Unilateral contraction causes ipsilateral lateral flexion (tilts head to same side) and contralateral rotation (turns head to opposite side). This combines the actions of the Sternomastoid and Cleidomastoid seen in comparative anatomy.

Trapezius Muscle Group

Function: Primarily responsible for moving and stabilizing the scapula (shoulder blade) during arm movements. It also helps to extend the head and neck. In many animals, this group is differentiated into several distinct parts (e.g., Clavotrapezius, Acromiotrapezius, Spinotrapezius) reflecting varied actions.

Clavotrapezius Muscle

Origin: Mid-dorsal raphe of the neck and occipital bone.

Insertion: Clavicle (clavicular raphe).

Action: Elevates and protracts the forelimb, and rotates the head and neck. In some species, it acts to pull the clavicle forward.

Acromiotrapezius Muscle

Origin: Spinous processes of cervical vertebrae (C2-C5) and mid-dorsal raphe of the neck.

Insertion: Scapular spine and acromion process.

Action: Elevates the scapula and draws it forward, aiding in movements of the shoulder blade, particularly protraction and rotation.

Spinotrapezius Muscle

Origin: Spinous processes of thoracic vertebrae (T3-T10).

Insertion: Scapular spine.

Action: Draws the scapula dorsally (backward) and caudally (posteriorly), assisting in shoulder blade retraction and depression.

Deltoid Muscle Group

Function: This group forms the rounded contour of the shoulder. It is involved in various movements of the shoulder joint and the humerus (upper arm bone), including abduction, flexion, extension, and rotation of the arm. It is often divided into clavicular, acromial, and spinal parts (e.g., Clavodeltoid, Acromiodeltoid, Spinodeltoid).

Clavodeltoid Muscle

Origin: Clavicle.

Insertion: Deltoid ridge of the humerus.

Action: Functions in flexion and adduction of the forelimb (upper arm) at the shoulder joint.

Acromiodeltoid Muscle

Origin: Acromion process of the scapula.

Insertion: Deltoid ridge of the humerus.

Action: Primarily responsible for the abduction of the forelimb (moving it away from the body) at the shoulder joint.

Spinodeltoid Muscle

Origin: Spine of the scapula.

Insertion: Deltoid ridge of the humerus.

Action: Contributes to the extension and abduction of the forelimb at the shoulder joint.

Levator Scapulae Ventralis Muscle

Origin: Occipital bone (back of the skull, from the nuchal line) & transverse processes of the atlas (C1, the first cervical vertebra) and C2-C4 vertebrae.

Insertion: Scapula (specifically the metacromion, a process on the scapula, and vertebral border superior to the scapular spine).

Action: Acts to pull the scapula cranially (forward or upward towards the skull) and medially. It also can assist in neck extension and lateral flexion.

Latissimus Dorsi Muscle

Origin: Thoracolumbar fascia from the lower six thoracic spinous processes, all lumbar spinous processes, iliac crest, and the lower three or four ribs.

Insertion: Bicipital groove (intertubercular sulcus) of the humerus (upper arm bone).

Action: Primarily responsible for powerful extension, adduction, and internal rotation of the humerus/forelimb. It pulls the forelimb backward and acts as a powerful extensor of the shoulder joint.

Splenius Muscle

Origin: From the nuchal ligament (midline neck) and spinous processes of the C7 to T3-T6 upper thoracic vertebrae.

Insertion: Occipital bone (back of the skull, below superior nuchal line) and mastoid region (area around the mastoid process of the temporal bone).

Action: When both sides contract, it bilaterally extends and raises the head and neck. When one side contracts, it rotates and bends the head to the same side (ipsilateral rotation and lateral flexion).

Rhomboid Capitus Muscle

Origin: Occipital bone (nuchal line, near the skull base).

Insertion: Scapula (vertebral border, superior aspect).

Action: Elevates and retracts the scapula, pulling it cranially and medially. This muscle is more distinctly observed in some quadruped species.

Rhomboid Major Muscle

Origin: Spinous processes of thoracic vertebrae T2-T5.

Insertion: Medial border of the scapula (from the spine to the inferior angle).

Action: Retracts (adducts) the scapula, elevates the medial border of the scapula, and rotates it to depress the glenoid cavity. It is crucial for stabilizing the scapula against the thoracic wall.

Rhomboid Minor Muscle

Origin: Nuchal ligament and spinous processes of C7-T1 vertebrae.

Insertion: Medial border of the scapula (at the root of the spine).

Action: Retracts (adducts) the scapula and elevates its medial border, working synergistically with the Rhomboid Major to stabilize and move the scapula.

Serratus Ventralis Muscle

Origin: Lateral surfaces of ribs 1–10 (in some animals) & transverse processes of the cervical vertebrae (neck vertebrae, C3-C7).

Insertion: Medial surface of the scapula (the inner surface of the shoulder blade, along its vertebral border).

Action: Crucial for supporting the trunk between the forelimbs, it pulls the scapula ventrally (forward/anteriorly) and caudally (backward/posteriorly). It also protracts and rotates the scapula, playing a major role in shoulder stability.

Subscapularis Muscle

Origin: Subscapular fossa of the scapula (anterior surface of the shoulder blade).

Insertion: Lesser tubercle of the humerus.

Action: Primarily medially rotates the humerus and is a strong adductor. It is a key component of the rotator cuff, helping to stabilize the shoulder joint and prevent anterior displacement of the humeral head.

Teres Major Muscle

Origin: Dorsal surface of the inferior angle and lower part of the lateral border of the scapula.

Insertion: Medial lip of the bicipital groove (intertubercular sulcus) of the humerus.

Action: Extends, powerfully adducts, and medially rotates the humerus at the shoulder joint. It works synergistically with the Latissimus Dorsi.

Teres Minor Muscle

Origin: Upper two-thirds of the lateral border of the scapula.

Insertion: Inferior aspect of the greater tubercle of the humerus.

Action: Primarily laterally rotates the humerus and weakly contributes to abduction. It is an important part of the rotator cuff, contributing to shoulder joint stability.

Supraspinatus Muscle

Origin: Supraspinous fossa of the scapula (above the scapular spine).

Insertion: Superior aspect of the greater tubercle of the humerus.

Action: Initiates abduction of the humerus (first 15 degrees) and stabilizes the humeral head in the glenoid cavity. It is a crucial rotator cuff muscle.

Scalenes Muscles (Anterior, Middle, Posterior)

Origin: Transverse processes of the cervical vertebrae (C3-C7).

Insertion: Superior surfaces of ribs 1–2.

Action: When both sides contract, they elevate ribs 1 and 2 during forced inhalation (acting as accessory muscles for respiration). Unilateral contraction performs lateral flexion of the neck to the same side and slight rotation of the head. The anterior, middle, and posterior scalene muscles work together for these actions, with varying degrees of emphasis based on their specific attachments and fiber direction.

External Intercostals Muscles

Origin: Inferior border of the rib above.

Insertion: Superior border of the rib below.

Action: Elevate the ribs during quiet and forced inspiration. This action increases the volume of the thoracic cavity by moving the ribs up and out, facilitating air intake into the lungs.

Internal Intercostals Muscles

Origin: Superior border and costal groove of the rib below.

Insertion: Inferior border of the rib above (between costal cartilage and angle).

Action: Depress the ribs during forced expiration. This action decreases the volume of the thoracic cavity by moving the ribs down and in, aiding in expelling air from the lungs.

Rectus Abdominis Muscle

Origin: Pubic crest and pubic symphysis.

Insertion: Xiphoid process and costal cartilages of ribs 5-7.

Action: Flexes the vertebral column (bending forward), especially the lumbar spine, and compresses abdominal contents. It is also involved in forced expiration and in childbirth/defecation.

External Oblique Muscle

Origin: External surfaces of ribs 5-12.

Insertion: Linea alba, pubic tubercle, and anterior half of the iliac crest.

Action: Unilateral contraction rotates the trunk to the opposite side and laterally flexes it to the same side. Bilateral contraction flexes the vertebral column and compresses abdominal contents, contributing to forced expiration.

Internal Oblique Muscle

Origin: Thoracolumbar fascia, anterior two-thirds of the iliac crest, and lateral half of the inguinal ligament.

Insertion: Costal cartilages of ribs 10-12, linea alba, and pubic crest.

Action: Unilateral contraction rotates the trunk to the same side and laterally flexes it to the same side. Bilateral contraction flexes the vertebral column and compresses abdominal contents.

Transversus Abdominis Muscle

Origin: Internal surfaces of costal cartilages of ribs 7-12, thoracolumbar fascia, iliac crest, and lateral third of the inguinal ligament.

Insertion: Linea alba and pubic crest.

Action: Compresses abdominal contents, forming a natural "corset" that increases intra-abdominal pressure. It plays a key role in stabilizing the trunk and in forced expiration.

Linea Alba

Description: A fibrous band that runs vertically along the midline of the anterior abdominal wall. It is formed by the fusion of the aponeuroses of the abdominal muscles (external oblique, internal oblique, and transversus abdominis). It serves as a central attachment point for these muscles and helps define the "six-pack" appearance.

Pectoantebrachialis Muscle

Origin: Cranial part of the sternum.

Insertion: Fascia of the forearm, near the elbow.

Action: Adducts the forelimb. It is a superficial pectoral muscle in many quadrupeds, often absent in humans.

Pectoralis Major Muscle

Origin: Medial half of the clavicle, sternum (breastbone), and costal cartilages of the upper six ribs.

Insertion: Lateral lip of the bicipital groove (intertubercular sulcus) of the proximal humerus (the upper part of the upper arm bone).

Action: Primarily adducts (draws toward the midline), medially rotates, and flexes the humerus/forelimb at the shoulder joint.

Pectoralis Minor Muscle

Origin: Anterior surfaces of ribs 3-5.

Insertion: Coracoid process of the scapula (a small hook-like process on the lateral edge of the superior anterior portion of the scapula).

Action: Depresses and protracts the scapula (draws it forward and downward) and also draws the forelimb toward the midline and backward. It can also assist in forced inspiration by elevating the ribs.

Xiphihumeralis Muscle

Origin: Xiphoid process of the sternum.

Insertion: Ventral surface of the humerus.

Action: Adducts the forelimb. It runs caudally from the pectoralis minor and is often seen in cats, typically absent in humans.

Triceps Brachii Muscle

Origin: Long head originates from the infraglenoid tubercle of the scapula (shoulder blade); Lateral head originates from the posterior surface of the humerus (above the radial groove); Medial head originates from the posterior surface of the humerus (below the radial groove).

Insertion: Olecranon of ulna (the bony projection of the forearm bone that forms the elbow).

Action: The primary powerful extensor of the forearm at the elbow joint. The long head also assists in adduction and extension of the shoulder.

Anconeus Muscle

Origin: Lateral epicondyle of the humerus.

Insertion: Olecranon and posterior surface of the ulna.

Action: Assists the triceps in extending the forearm at the elbow joint and stabilizes the elbow joint.

Brachialis Muscle

Origin: Anterior surface of the humerus, distal to the deltoid tuberosity.

Insertion: Tuberosity and coronoid process of the ulna.

Action: A powerful flexor of the forearm at the elbow joint.

Clavobrachialis Muscle

Origin: Clavicle.

Insertion: Ulna (proximal medial surface) and often merges with the common tendon of the biceps brachii.

Action: Flexes and adducts the forearm. This muscle is prominent in some animals (e.g., cats) and is often intimately associated with the deltoid group.

Biceps Brachii Muscle

Origin: Long head originates from the supraglenoid tubercle of the scapula (near the glenoid cavity); Short head originates from the coracoid process of the scapula.

Insertion: Radial tuberosity of the radius (the lateral bone of the forearm) and via the bicipital aponeurosis into the deep fascia of the forearm.

Action: Primarily flexes the forearm at the elbow joint and powerfully supinates (rotates the palm/paw upward) the forearm. It also weakly flexes the shoulder.

Epitrochlearis Muscle

Origin: Lateral surface of the latissimus dorsi or medial epicondyle of the humerus.

Insertion: Olecranon process of the ulna.

Action: Extends the elbow and assists in adduction of the arm. This muscle is typically found in many quadrupeds (e.g., cats) but is generally absent in humans.

Brachioradialis Muscle (Supinator Longus)

Origin: Lateral supracondylar ridge of the humerus.

Insertion: Styloid process of the radius.

Action: Flexes the forearm at the elbow, and can pronate or supinate the forearm to a neutral position, particularly during rapid movements. "Supinator longus" is an older term, especially in cat anatomy; "Brachioradialis" is the current term in human anatomy.

Extensor Carpi Radialis Longus Muscle

Origin: Lateral supracondylar ridge of the humerus.

Insertion: Base of the second metacarpal bone.

Action: Extends and abducts the hand at the wrist joint.

Extensor Carpi Radialis Brevis Muscle

Origin: Lateral epicondyle of the humerus.

Insertion: Base of the third metacarpal bone.

Action: Extends and abducts the hand at the wrist joint.

Extensor Digitorum Communis Muscle

Origin: Lateral epicondyle of the humerus.

Insertion: Extensor expansions of the medial four digits (fingers/toes), inserting onto the middle and distal phalanges.

Action: Extends the medial four digits at the metacarpophalangeal and interphalangeal joints, and also extends the wrist.

Extensor Digitorum Lateralis Muscle

Origin: Lateral epicondyle of the humerus.

Insertion: Extensor expansions of digits 2-5 (usually focused on 4th and 5th digits).

Action: Extends the lateral digits of the hand/forepaw and contributes to wrist extension, particularly in comparative anatomy.

Extensor Carpi Ulnaris Muscle

Origin: Lateral epicondyle of the humerus and posterior border of the ulna.

Insertion: Base of the fifth metacarpal bone.

Action: Extends and adducts the hand at the wrist joint.

Extensor Pollicis Brevis Muscle

Origin: Posterior surface of the radius and interosseous membrane.

Insertion: Dorsal aspect of the base of the proximal phalanx of the thumb (pollex/digit 1).

Action: Extends the thumb at the carpometacarpal and metacarpophalangeal joints.

Supinator Muscle

Origin: Lateral epicondyle of the humerus, radial collateral ligament, annular ligament, and supinator crest of the ulna.

Insertion: Lateral, posterior, and anterior surfaces of the proximal third of the radius.

Action: Powerfully supinates the forearm (rotates the palm anteriorly or superiorly).

Flexor Carpi Ulnaris Muscle

Origin: Humeral head: Medial epicondyle of the humerus; Ulnar head: Olecranon and posterior border of the ulna.

Insertion: Pisiform bone, hook of the hamate, and base of the fifth metacarpal bone.

Action: Flexes and adducts the hand at the wrist joint.

Flexor Carpi Radialis Muscle

Origin: Medial epicondyle of the humerus.

Insertion: Bases of the second and third metacarpal bones.

Action: Flexes and abducts the hand at the wrist joint.

Flexor Digitorum Profundus Muscle

Origin: Anterior and medial surfaces of the ulna and interosseous membrane.

Insertion: Bases of the distal phalanges of digits 2-5.

Action: Flexes the distal interphalangeal joints of digits 2-5, and also flexes the wrist and metacarpophalangeal joints.

Pronator Teres Muscle

Origin: Humeral head: Medial epicondyle of the humerus; Ulnar head: Coronoid process of the ulna.

Insertion: Lateral surface of the radius, mid-shaft.

Action: Pronates the forearm (rotates the palm posteriorly or inferiorly) and weakly flexes the elbow.

Palmaris Longus Muscle

Origin: Medial epicondyle of the humerus.

Insertion: Palmar aponeurosis and flexor retinaculum.

Action: Flexes the wrist and tenses the palmar aponeurosis. This muscle is often absent in some individuals.

Tensor Fascia Latae Muscle

Origin: Anterior superior iliac spine (ASIS) and anterior part of the outer lip of the iliac crest (a part of the hip bone).

Insertion: Iliotibial tract (ITT), a thick band of fascia on the lateral aspect of the thigh, which then inserts into the lateral condyle of the tibia.

Action: Tenses the fascia lata, flexes the hip, and abducts (moves away from the midline) and medially rotates the thigh. It also helps stabilize the knee in extension.

Lateral Fascia (Iliotibial Tract)

Description: The Iliotibial Tract (ITT) is a thick, fibrous band of fascia that runs along the lateral aspect of the thigh, extending from the iliac crest to the lateral condyle of the tibia. It serves as an insertion point for the Tensor Fascia Latae and Gluteus Maximus muscles, playing a crucial role in stabilizing the hip and knee during walking and running.

Gluteus Medius Muscle

Origin: Outer surface of the ilium (between the anterior and posterior gluteal lines).

Insertion: Greater trochanter of the femur.

Action: Primarily abducts (moves away from the midline) the thigh at the hip joint. The anterior fibers also medially rotate and flex the thigh, while the posterior fibers laterally rotate and extend the thigh.

Gluteus Maximus Muscle

Origin: Posterior gluteal line of the ilium, dorsal surface of the sacrum and coccyx, and sacrotuberous ligament.

Insertion: Gluteal tuberosity of the femur and the iliotibial tract (ITT).

Action: The most powerful extensor of the thigh at the hip joint. It also acts to abduct (moves away from the midline) and laterally rotate the thigh, especially during powerful movements like climbing stairs.

Caudofemoralis Muscle

Origin: Transverse processes of the caudal vertebrae (tail vertebrae, typically C1-C3 in some species).

Insertion: Patella/tibia via fascia (kneecap/shin bone through connective tissue, often inserting into the lateral aspect of the patella or fascia lata).

Action: Primarily abducts (moves away from the midline) the thigh and assists in extending the shank (lower leg). This muscle is prominent in some species like cats, but not typically a distinct muscle in humans.

Biceps Femoris Muscle (Hamstring)

Origin: Long head: Ischial tuberosity; Short head: Linea aspera and lateral supracondylar line of the femur.

Insertion: Head of the fibula and lateral condyle of the tibia.

Action: Flexes the knee and extends the hip. The long head also assists in lateral rotation of the hip.

Semitendinosus Muscle (Hamstring)

Origin: Ischial tuberosity.

Insertion: Medial surface of the proximal tibia (as part of the pes anserinus).

Action: Flexes the knee, extends the hip, and medially rotates the leg (especially when the knee is flexed).

Semimembranosus Muscle (Hamstring)

Origin: Ischial tuberosity.

Insertion: Posterior medial condyle of the tibia.

Action: Flexes the knee, extends the hip, and medially rotates the leg (especially when the knee is flexed).

Sartorius Muscle

Origin: Anterior superior iliac spine (ASIS) (a prominent part of the hip bone).

Insertion: Medial proximal tibia (shin bone), specifically near the medial condyle, as part of the pes anserinus.

Action: Often called the "tailor's muscle". It uniquely flexes the hip and the knee, abducts the thigh, and laterally rotates the thigh, allowing for cross-legged sitting.

Gracilis Muscle

Origin: Inferior ramus of the pubis and ischial ramus (parts of the pelvic bone).

Insertion: Medial surface of the proximal tibia (the inner side of the shin bone), as part of the pes anserinus.

Action: Adducts (draws toward the midline) the thigh, flexes the knee, and medially rotates the leg, particularly when the knee is flexed.

Rectus Femoris Muscle (Quadriceps Group)

Origin: Anterior inferior iliac spine (AIIS) and ilium superior to the acetabulum.

Insertion: Patella via the quadriceps tendon, continuing as the patellar ligament to the tibial tuberosity.

Action: Extends the knee and flexes the hip. It is the only quadriceps muscle that crosses the hip joint.

Vastus Lateralis Muscle (Quadriceps Group)

Origin: Greater trochanter, intertrochanteric line, and linea aspera of the femur.

Insertion: Patella via the quadriceps tendon, continuing as the patellar ligament to the tibial tuberosity.

Action: Extends the knee.

Vastus Medialis Muscle (Quadriceps Group)

Origin: Intertrochanteric line, pectineal line, and linea aspera of the femur.

Insertion: Patella via the quadriceps tendon, continuing as the patellar ligament to the tibial tuberosity.

Action: Extends the knee and stabilizes the patella.

Vastus Intermedialis Muscle (Quadriceps Group)

Origin: Anterior and lateral surfaces of the femur shaft.

Insertion: Patella via the quadriceps tendon (deep to rectus femoris), continuing as the patellar ligament to the tibial tuberosity.

Action: Extends the knee.

Adductor Femoris Muscle

Origin: Pubis (inferior ramus) and ischium (ischial tuberosity).

Insertion: Linea aspera of the femur (posterior aspect of the thigh bone).

Action: Primarily adducts (draws toward the midline) and medially rotates the thigh at the hip joint. It also assists in hip flexion.

Adductor Longus Muscle

Origin: Pubic body, inferior to the pubic crest.

Insertion: Linea aspera of the femur (middle third).

Action: Adducts the thigh and assists in hip flexion.

Pectineus Muscle

Origin: Pectineal line of the pubis.

Insertion: Pectineal line of the femur (between lesser trochanter and linea aspera).

Action: Adducts and flexes the thigh at the hip joint, also medially rotates the thigh.

Iliopsoas Muscle

Origin: Iliacus originates from the iliac fossa (part of the hip bone); Psoas Major originates from the lumbar vertebrae (lower back vertebrae - transverse processes and vertebral bodies of T12-L5).

Insertion: Lesser trochanter (a prominent projection on the medial and posterior side of the femur).

Action: The strongest flexor of the hip joint. It is essential for walking, running, and maintaining posture.

Femoral Triangle

Description: A triangular depression located in the superomedial part of the anterior thigh. Its boundaries are: superiorly by the inguinal ligament, medially by the adductor longus muscle, and laterally by the sartorius muscle. It contains important neurovascular structures, including the femoral nerve, femoral artery, femoral vein, and lymphatic vessels (from lateral to medial: NAVEL).

Gastrocnemius Muscle (Triceps Surae Group)

Origin: Lateral head: Lateral condyle and posterior surface of the femur; Medial head: Medial condyle and posterior surface of the femur.

Insertion: Posterior surface of the calcaneus (heel bone) via the Achilles tendon.

Action: Plantarflexes the foot at the ankle joint and flexes the knee joint. It is a powerful propulsor during walking and running.

Soleus Muscle (Triceps Surae Group)

Origin: Posterior surface of the head of the fibula and its superior third, and the soleal line of the tibia.

Insertion: Posterior surface of the calcaneus (heel bone) via the Achilles tendon.

Action: Powerful plantarflexor of the foot at the ankle joint. Unlike the gastrocnemius, it does not cross the knee joint.

Plantaris Muscle (Triceps Surae Group)

Origin: Lateral supracondylar ridge of the femur and oblique popliteal ligament.

Insertion: Posterior surface of the calcaneus (heel bone) via the Achilles tendon or adjacent to it.

Action: Weakly assists in plantarflexion of the foot and knee flexion. Its long, slender tendon makes it sometimes referred to as 'freshman's nerve' due to its appearance upon dissection.

Peroneus Muscle Group (Fibularis Longus, Brevis, Tertius)

Origin: Lateral condyle of the tibia, head and shafts of fibula. (Specific origins vary per muscle: Longus - head & superior fibula; Brevis - inferior fibula; Tertius - anterior fibula).

Insertion: First metatarsal, medial cuneiform, and fifth metatarsal bones of the foot. (Specific insertions vary: Longus - 1st metatarsal & medial cuneiform; Brevis - 5th metatarsal; Tertius - base of 5th metatarsal).

Action: Primarily responsible for powerful plantarflexion of the foot (pointing the toes downward) and eversion of the foot (turning the sole of the foot outward, away from the midline of the body). They are crucial for lateral ankle stabilization, preventing inversion sprains. Fibularis tertius assists in dorsiflexion and eversion.

Extensor Digitorum Longus Muscle

Origin: Lateral condyle of the tibia, anterior surface of the fibula, and interosseous membrane.

Insertion: Via four tendons to the dorsal surfaces of the middle and distal phalanges of the lateral four digits (toes).

Action: Primarily extends the digits (toes, specifically the lateral four) at the metatarsophalangeal and interphalangeal joints, and also dorsiflexes (pulls the foot/toes upward) the foot at the ankle joint.

Achilles Tendon (Calcaneal Tendon)

Description: This is the thickest and strongest tendon in the body. It is a common tendon formed by the junction of the gastrocnemius, soleus, and plantaris muscles (the triceps surae group), inserting onto the posterior aspect of the calcaneus (heel bone). It transmits the force of these calf muscles to the foot for powerful plantarflexion and propulsion, crucial for walking, running, and jumping.

Flexor Digitorum Longus Muscle

Origin: Posterior surface of the tibia, inferior to the soleal line.

Insertion: Plantar surfaces of the distal phalanges of digits 2-5 (toes).

Action: Flexes the lateral four toes (digits 2-5) at the interphalangeal and metatarsophalangeal joints, and also plantarflexes the ankle and supports the longitudinal arch of the foot.

Tibialis Anterior Muscle

Origin: Lateral condyle and upper half to two-thirds of the lateral surface of the tibia, and the interosseous membrane.

Insertion: Medial cuneiform bone and base of the first metatarsal bone.

Action: Primarily dorsiflexes the foot (pulls the foot upward) at the ankle joint and inverts the foot (turns the sole medially). It also helps support the medial longitudinal arch of the foot.

Flexor Hallucis Longus Muscle

Origin: Posterior surface of the fibula (inferior two-thirds) and interosseous membrane.

Insertion: Plantar surface of the distal phalanx of the great toe (hallux/digit 1).

Action: Flexes the great toe (hallux) at the interphalangeal and metatarsophalangeal joints. It also plantarflexes the ankle and supports the medial longitudinal arch of the foot, playing a crucial role in pushing off during gait.