Anatomy I: Lesson 10

Myologia – Part I Objective: Students will examine the muscles of a canine in order to identify the musculature of the body.

Practical Tasks

1) m. latissimus dorsi, m. trapezius, m. rhomboideus, m. serratus ventralis, mm. pectorales

2) extensors of the shoulder

3) flexors of the shoulder

4) extensors of the elbow

5) flexors of the elbow

Practical Task 1

M. latissimus dorsi Origin: superficial layer of thoracolumbar

fascia (from spinous processes of the last 7-8 thoracic and lumbar vertebrae); also muscular attachment proximally to the last few ribs

Insertion: on teres major tuberosity (together with m. teres major)

Action: draws free limb caudally; together with m. teres major flexes shoulder

1) M. latissimus dorsi : one of the largest muscles of the body, flat, almost triangular in shape, on dorsal and lateral side of thorax.

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Origin

by aponeurois from the Fascia thoracolumbalis

Insertion

Tuberositas teres major resp. Crista tuberositas minoris (in Ca.) of the humerus

Innervated by

N. thoracodorsalis and Nn. pectorales caudales

Actions

antagonist to the M. brachiocephalicus. It retracts the free limb when shoulder is flexed; prevents arching of vertebral column when pulling a load; it also draws the trunk forward over the fixed limb

Musculature of the Pectoral Girdle Extrinsic = Superficial Musculature

1) M. trapezius :

immediately under the skin on lateral surface of neck and withers region, triangular when seen from the side

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Origin

mid-dorsal raphe and supraspinous ligament

Insertion

spine of the scapula

Body

two parts, cervical and thoracic separated by aponeurosis

Innervated by

dorsal branch of N. Accessorius

Actions

stabilize shoulders ◦ raises scapula against the trunk ◦ lift and advance the limb ◦ abduct the limb when sidestepping

Musculature of the Pectoral Girdle Extrinsic = Superficial Musculature

4) M. serratus ventralis : covered entirely by M. trapezius and M. latissimus dorsi; the strongest and most important muscle of the „muscular sling“; all along fan shaped;

Body of two (2) parts:

• (cranially): cervicis • (caudally): thoracis → most

important weight bearing element of pectoral girdle

Origin

• of pars cervicis: from transverse processes of the: 1st to 7th cervical vertebrae (Su) and 2nd-3rd to 7th cervical vertebrae (Ca, Bo, Eq)

• of pars thoracis: from middle of thoracal ribs 1st to 7th (to max. 9-10th)

Innervated by

N. thoracis longus (→ M. ser.ventr.thoracis) and ventral branches of long thoracic nerve

Insertion

dorsal part of medial cartilagenous surface of scapula → Facies serrata

Actions

supporting the weight of the trunk. At fixed limb the cervical part raises the neck whole the thoracic part lifts/propells the trunk forewards; aid also in forced inspiration when forelimbs are abducted; the thoracic part can move the unweighted limb forewards.

Musculature of the Pectoral Girdle Intrinsic = Deep Musculature

4) M. serratus ventralis

Musculature of the Pectoral Girdle Intrinsic = Deep Musculature

5) Mm. pectorales superficiales :

in domestic mammals less developed than the deep pectoral muscle. With 2 heads:

cranially: M. pectoralis descendens

more caudally: M. pectoralis transversus

The superficial and deep pectoral muscles make a powerful ventral sling between ventral chest wall and the forelimbs.

Musculature of the Pectoral Girdle Extrinsic = Superficial Musculature

Origin

• descendens → manubrium of sternum

• transversus → ventrally from 1st to 3rd costal cartilages (in Ca)

→ from 1st to 6th costal cartilages (Eq, Bo, Su)

Insertion

• of descendens (cranial): Crista humeri distal to the deltoid tuberosity.

• Of transverse (caudal): covers the elbow joint to insert on → the medial Fascia antebrachii (Ca), and → Crista humeri (Ungulates)

Innervated by

Nn. pectorales

Actions

ventral connection between thoracic limb and trunk; abduct the forelimb, pull limb either forwards or backwards (depending on position); pulls the trunk to the side when limb is fixed

5) Mm. pectorales superficiales :

Musculature of the Pectoral Girdle Extrinsic = Superficial Musculature

1) M. pectoralis profundus : In domestic mammals much better developed than the superficial ones. With variations of the insertions between species.

Origin

sternum and cartilages of true ribs, occasionally also xiphoid region, or deep fascia of trunk (Eq, Ca) Insertion

(varies from species to species): → Ca: mainly to Tuberculum majus of the humerus → Su: only to Tuberculum minus → Eq: both to Tuberculi majus and minus

Actions

supporting trunk and retracting unsupported limb (→ synergist with latissimus dorsi); also extends and fixes shoulder joint, and pulls the trunk forward (when limb is advanced and fixed)

Intrinsic = Deep Musculature

Musculature of the Pectoral Girdle

Practical Task 2

Extensors of the Shoulder

General considerations:

There are four (4) muscles of the a) LATERAL group:

1, supraspinatus, 2, infraspinatus, 3, deltoid, 4, teres minor and also four (4) of the b) MEDIAL group:

1, teres major, 2, articularis humeri, 3, subscapular, 4, coracobrachialis

Muscles of the Shoulder Joint

Lateral muscles

1) M. Supraspinatus: a strong muscle

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Origin

fossa supraspinata of scapula

Insertion

Ca Su, Bo Eq

Tuberculum majus of humeri (with one tendon)

Tuberculum majus humeri (with branched tendon); in Un. also onto Tuberculum minus humeri

Medial and lateral tuberosites humeri

Innervated by

N. suprascapularis

Actions

fix and extend shoulder joint, and helps in bearing weight of body

Muscles of the Shoulder Joint

2) M. infraspinatus : also a strong muscle Origin

infraspinous fossa of and spine of the scapula Insertion

Tubercles majus of the humerus

Innervated by

N. suprascapularis of the brachial plexus Actions

can act as contractile collateral ligament assist in flexion or extension (according to position of insertion points) in Ca: assists supination and abduction of humerus also a flexor when joint is fixed.

Muscles of the Shoulder Joint Lateral muscles

Practical Task 3

Flexors of the Shoulder

◦ M. supraspinatus and M. Infraspinatus described in task 2

◦ Act as both a flexor and extensor

3) M. deltoideus : a flattened muscle directly under the skin

Body of two (2) parts in Ca, Ru:

• pars acromialis • pars scapularis

◦ in animals without distinct acromion (Eq, Su) the two parts are fused

Origin

(of pars acromialis): the spine and the caudal margin of the scapula

Insertion

deltoid tuberosity of the humerus

Innervated by

N. axillaris of the brachial plexus

Actions

flexor of shoulder joint and abducting the limb

Muscles of the Shoulder Joint Lateral muscles

4) M. teres minor : a small muscle on caudolateral aspect of shoulder joint under the deltoid

Origin

distal third of caudal margin of the scapula

Insertion

just above deltoid tuberosity of humerus or on the tricipital line

Innervated by

humerus or on the tricipital line

Actions

to flex shoulder joint

Muscles of the Shoulder Joint Lateral muscles

Medial muscles

1) M. teres major : a long, flattened, fleshy muscle

Origin

dorsal part of the caudal scapula

Insertion

Tuberositis teres majoris of humerus

Innervated by

N. axillaris of the brachial plexus Actions

flex shoulder joint; to a small degree also adducting the limb

Muscles of the Shoulder Joint

Practical Task 4:

Extensors of the Elbow ◦ M. triceps brachii

Caput longum

Caput laterale

Caput mediale

Caput accessorium

◦ M. tensor fasciae antebrachii

◦ M. anconeus

1) M. triceps brachii : the strongest muscle of the thorcic limb; activates two joints

Body :

in all domestic mammals with four (4) heads except Eq, (3 heads) ◦ caput longum ◦ caput laterale ◦ caput mediale ◦ caput accesory (not in Eq) Origin

◦ of caput longum: → caudal border of scapula ◦ of caput laterale: → laterally from humerus near the deltoid tuberosity ◦ of caput mediale: → medial aspect of shaft of humerus near the teres tubercle ◦ of caput accessorium: → caudally near head of the humerus

Insertion

on olecranon process of ulna (by all 4 heads)

Innervated by

N. radialis from the brachial plexus Actions

extend the elbow joint; the long head also flexes the shoulder joint; in standing animal it greatly participates in the passive „stay apparatus“ by fixing the elbow.

Muscles of the Elbow Joint Extensors

1) M. triceps brachii : the strongest muscle of the thoracic limb; activates two joints

Muscles of the Elbow Joint Flexors

2) M. anconeus : a small, powerful muscle covered by triceps; could be viewed as part of triceps brachii

Insertion

laterally on olecranon

Origin

distal half of caudal border of humerus and lateral and medial epicondyles

Innervated by

N. radialis of the brachial plexus Actions

extending the elbow joint

Muscles of the Elbow Joint Flexors

Practical Task 4

Flexors of the Elbow ◦ M. Biceps brachii

◦ M. Brachialis

2) M. biceps brachii : a spindle-shaped muscle, acting on two (2) joints; its proximal tendon crosses the capsule of the shoulder joint (in: Ca, Su and sheep), resp. it is protected by large intertuberal bursa (in: goat, Bo, Eq)

Origin

supraglenoid tuberosity of the scapula

Insertion

after the elbow joint its distal tendon dividing into two, inserting to medial tuberosity of both the proximal radius and adjacent ulna

Innervated by

N. musculocutaneus from the brachial plexus

Actions

flex elbow joint and also to extend the shoulder; in Eq: a long superficial tendin (→ lacertus fibrosus) joining the antebrachial fascia, eventually inserting on metacarpal tuberosity → transmitting action of biceps into carpal joint → functioning mainly as passive „stay

Muscles of the Elbow Joint Flexors

1) M. brachialis : fleshy, long-fibred muscle, winding over lateral surfce of humerus and crossing the biceps obliquely

Origin

caudally below the head of the humerus

Insertion

on both radius and ulna between M. biceps femoris and

M. extensor carpi radialis

Innervated by

N. musculocutaneus of the brachial plexus

Actions

flex and lift elbow joint

Muscles of the Elbow Joint Flexors