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Forelimb - Anatomy & Physiology (view source)
Revision as of 19:33, 27 October 2022
, 19:33, 27 October 2022no edit summary
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==Common Structures of the Proximal Forelimb and Shoulder==
===Scapula===
The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk. In ungulates, the dorsal border is extended by a scapular cartilage, which enlarges the area for muscle attachment. This ossifies with age. The bone is roughly triangular, with a prominent '''spine''' that can be palpated through the skin.
:The spine:
::defines '''infraspinous''' and '''supraspinous''' '''fossae''', inhabited by the infraspinatus and supraspinatus muscles respectively
::serves as a point of attachment for the '''trapezius''' muscle
::culminates in the '''acromion''' in all but the horse and pig.
::the cat also possesses a suprahamate process which lies proximal to the acromion and projects caudally.
Just cranial to the glenoid cavity can be seen a bony prominence called the supraglenoid tubercle which is the origin of the biceps bracii muscle
Medial muscle attachment consist mostly of the '''subscapularis''', with the '''serratus ventralis''' attaching dorsally. The Scapula articulates with the humerus at the '''glenoid cavity'''.
===Clavicle===
===Clavicle===
The Clavicle is all but absent in most domestic species, with the notable exception of the avian skeleton. In the dog and cat, a remnant of bone may remain embedded in the fibrous intersection in the brachiocephalicus, which may prove misleading in radiographic images.
The Clavicle is all but absent in most domestic species, with the notable exception of the avian skeleton. In the dog and cat, a remnant of bone may remain embedded in the fibrous intersection in the brachiocephalicus muscle, which may prove misleading in radiographic images.
===Humerus===
===Humerus===
The Humerus is the long bone of the forearm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.
The Humerus is the long bone of the arm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.
The head of the humerus comprises '''greater''' and '''lesser tubercles''', separated by an '''intertubercular groove''' through which runs the tendon of the '''biceps brachii'''. The shaft of the humerus takes on a characteristically twisted shape via a groove carrying the '''brachialis''' and '''radial nerve'''. Laterally, the '''deltoid tuberosity''' is palpable through the skin and connects to the head of the humerus via a ridge and merges distally with the '''crest of the humerus'''. Distally, the humerus culminates in a '''condyle''' which articulates to form the elbow.
:In large animals, it meets the radius via a '''trochlea'''
:In dogs and cats, it articulates with the ulna medially via a trochlea and the radius laterally via a '''capitulum'''
:Caudally, all species show an '''olecranon fossa''' which articulates with the '''olecranon''' of the ulna
At the distal end of the humerus a small hole may be seen connecting the olecranon fossa caudally with the radial fossa cranially. This is the supratrochlear foramen. No structures pass through it.
Medial and lateral epicondyles provide attachment for flexors and extensors of the carpus and digits.
==Joints of the Proximal Forelimb==
==Joints of the Proximal Forelimb==
===Shoulder Joint===
===Shoulder Joint===
The shoulder joint links the humerus and the scapula at the '''glenoid cavity''', which is much smaller than the head of the humerus. While structually it is a [[Joints - Anatomy & Physiology#Types of Joints|'''ball and socket''']] joint, it functions as a [[Joints - Anatomy & Physiology#Types of Joints|'''hinge joint''']] due to extensive muscling around the articulation. The joint capsule is enlarged and extends under the tendon of the biceps, acting as a synovial sheath to protect the tendon.
The shoulder joint links the humerus and the scapula at the '''glenoid cavity''', which is much smaller than the head of the humerus. While structurally it is a [[Joints - Anatomy & Physiology#Types of Joints|'''ball and socket''']] joint, it functions as a [[Joints - Anatomy & Physiology#Types of Joints|'''hinge joint''']] due to extensive muscling around the articulation. The joint capsule is enlarged and extends under the tendon of the biceps, acting as a synovial sheath to protect the tendon.
It is important to distinguish the shoulder/scapulohumeral joint from the entirely muscular connection (synsarcosis) between the forelimb and the trunk. This latter connection is sometimes called the '''girdle muscles''', although this is a problematic term, because many of its constituent muscles do not attach to a limb girdle muscle. At Cambridge University, it has for some time been given the name '''omothoracic junction''', but this term has not entered common usage.
There are no true ligaments in the shoulder joint. The tendons of insertion of the supraspinatous and infraspinatous muscles cross the shoulder joint and insert laterally on the greater tubercle of the humerus. The tendon of the subscapularis inserts medially on the humerus. These act as 'ligaments' preventing dislocation of the shoulder.
===Elbow Joint===
===Elbow Joint===
Movement of the elbow joint is restricted to the [[Planes and Axes - Anatomy & Physiology|sagittal plane]]. It is bounded medially and laterally by collateral ligaments betweek the humerus and radius, caudally by the olecranon ligament between the humerus and olecranon, and further enforced by the annular radial ligament. The elbow is a compound joint including:
Movement of the elbow joint is restricted to the [[Planes and Axes - Anatomy & Physiology|sagittal plane]]. It is bounded medially and laterally by collateral ligaments between the humerus and radius, caudally by the olecranon ligament between the humerus and olecranon, and further enforced by the annular radial ligament. The elbow is a compound joint including:
*The [[Joints - Anatomy & Physiology#Types of Joints|'''hinge joint''']] between the humerus and the radius and ulna
*The [[Joints - Anatomy & Physiology#Types of Joints|'''hinge joint''']] between the humerus and the radius and ulna.
*The [[Joints - Anatomy & Physiology#Types of Joints|'''pivot joint''']] between the radius and ulna
*The [[Joints - Anatomy & Physiology#Types of Joints|'''pivot joint''']] between the radius and ulna.
*The point of the elbow, or the '''olecranon''' is formed by the anconeal process of the ulna inserting into the olecranon fossa of the humerus
*The point of the elbow, or the '''olecranon''' is formed by the anconeal process of the ulna inserting into the olecranon fossa of the humerus.
While in the human the radius and ulna are separated by an interosseus space and articulate only at their extremities, allowing for significant capability of supination and pronation, these movements are much more limited in domestic animals due to the gradual fusing of the two bones. The extreme case is exhibited by the horse.
While in the human the radius and ulna are separated by an interosseus space and articulate only at their extremities, allowing for significant capability of supination and pronation, these movements are much more limited in domestic animals due to the gradual fusing of the two bones. The extreme case is exhibited by the horse.
The radius forms the shaft-like rod of the distal limb, which is bowed to varying degrees amongst species. It articulates proximally with the distal humerus, caudally with the ulna, and distally with the carpus. Medially on the distal articular process, a '''styloid process''' projects, which is mirrored laterally by the ulna.
===Ulna===
===Ulna===
The Ulna's greatest contribution to functional anatomy is in the formation of the '''Olecranon''', or the point of the elbow, which gives rise to the attachment of the '''triceps'''. The olecranon articulates with the humerus via its anconeal process. Distally (where unfused), the '''lateral styloid process''' articulates with the '''ulnar carpal bone'''.
The Ulna's greatest contribution to functional anatomy is in the formation of the '''olecranon''', or the point of the elbow, which gives rise to the attachment of the '''triceps''' muscle. The olecranon articulates with the humerus via its anconeal process. The olecranon develops as an apophysis, i.e.. from a separate site of ossification. The trochlear notch on the cranial aspect of the ulna articulates with the large trochlea of the humerus which forms the main elbow joint capable of flexion and extension. Just distal to the trochlear notch, a large medial '''coronoid process''' and a smaller lateral coronoid process can be seen. Distally (where unfused), the '''lateral styloid process''' articulates with the '''ulnar carpal bone'''.
===Carpal bones===
===Carpal bones===
Carpal bones comprise two rows:
Carpal bones comprise two rows:
*Proximally, (mediolaterally), radial, intermediate, ulnar and accessory bones
*Proximally, (mediolaterally), radial, intermediate, ulnar and accessory bones. The accessory bone serves as a landmark for palpation.
*Distally, bones are numbered 1-5, though 5 is always fused with 4.
*Distally, bones are numbered 1-5, though 5 is always fused with 4
A small [[Bones - Anatomy & Physiology#Types of Bone|'''sesamoid''']] bone embedded in the medial tissues of the joint can sometimes be mistaken as a chip fracture.
===Metacarpal bones===
===Metacarpal bones===
The number of metacarpals varies widely among species, as the demand for their function changes: '''plantigrade''', or flat-footed, animals requiring the full complement of five metacarpal bones; the number is reduced in the upright stature of '''digitigrade''' animals such as the dog and cat, and shows the extreme in '''unguligrades''' like the horse, who depends entirely on the third metacarpal bone for its stature.
The number of metacarpals varies widely among species, as the demand for their function changes: '''plantigrade''', or flat-footed, animals requiring the full complement of five metacarpal bones; the number is reduced in the upright stature of '''digitigrade''' animals such as the dog and cat, and shows the extreme in '''unguligrades''' like the horse, which depends entirely on the third metacarpal bone for its stature.
Colloquially, the third metacarpal of the horse is known as the '''canon''' bone, and the vestigial 2 and 4 as '''splint bones'''
==Joints of the Distal Forelimb==
==Joints of the Distal Forelimb==
*The '''carpometacarpal joint''' between the distal carpal bones and the proximal metacarpals
*The '''carpometacarpal joint''' between the distal carpal bones and the proximal metacarpals
The joint is a synovial joint, comprised of a common outer fibrous capsule and three inner synovial pouches, one for each joint. Numerous ligaments add to the stability of the joint and ensure movement is largely limited to the [[Planes and Axes - Anatomy & Physiology|sagittal plane]], although no collateral ligaments exist in the dog between the radius and the proximal metacarpals. This allows a very small amount of rotation.
The joint is a synovial joint, compring a common outer fibrous capsule and three inner synovial pouches, one for each joint. Numerous ligaments add to the stability of the joint and ensure movement is largely limited to the [[Planes and Axes - Anatomy & Physiology|sagittal plane]], although no collateral ligaments exist in the dog between the radius and the proximal metacarpals. This allows a very small amount of rotation.
===Metacarpal Joint===
===Metacarpal Joint===
The metacarpal joint is defined by the presence of palmar [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|'''sesamoids''']], which allow the flexor tendons to pass over the sharp change in angle presented by the joint. These are paired on each digit, with the exception of the first digit where it exists.
The metacarpal joint is defined by the presence of palmar [[Bones - Anatomy & Physiology#Types of Bone|'''sesamoids''']], which allow the flexor tendons to pass over the sharp change in angle presented by the joint. They are paired on each digit, with the exception of the first digit where only one exists. A single '''dorsal sesamoid bone''' can also be seen in dogs in digit 2 - 5 inclusive over the same joint between the metacarpal bone and the proximal phalanx. This is not found in ungulates or in the the first digit. However another sesamoid bone exists in the tendon of the abductor pollicis longus muscle of the first digit.
==Muscles of the Forelimb==
==Muscles of the Forelimb==
===Extrinsic Musculature===
===Extrinsic Musculature===
These muscle are responsible for joining tht forelimb to the trunk, forming a synsarcosis rather than a conventional joint. Collectively, they act to transfer the weight of the body to the forelimbs as well as stabilize the scapula.
These muscle are responsible for joining the forelimb to the trunk, forming a synsarcosis rather than a conventional joint. Collectively, they act to transfer the weight of the body to the forelimbs as well as stabilize the scapula.
'''''Trapezius'''''
'''''Trapezius''''':
:Innervated by: Accessory n.
:Origin: mid-dorsal raphe and supraspinous ligament
:Insertion: spine of the scapula
:Body: two parts, cervical and thoracic separated by aponeurosis
:Action: raises scapula against the trunk and swings cranially to advance the limb
'''''Brachiocephalic m.'''''
'''''Brachiocephalic m.''''':
:Innervated by: Accessory n.
:Two parts separated by the clavicle where it exists
:Origin: clavicle or vestigial fibrous intersection
:Insertion: several places on the head and neck
:Actions:
::advances the limb and extends the shoulder joint when limb is in motion
::draws head and neck ventrally when limb is fixed
'''''Omotransversarius'''''
'''''Omotransversarius''''':
:Innervated by: Accessory n.
:Origin: transverse processes of the atlas
:Insertion: acromion and adjacent scapula
:Action: advancing the limb
'''''Latissimus dorsi'''''
'''''Latissimus dorsi''''':
:Innervated by: local branch of brachial plexus
:The '''broadest muscle of the back'''
:Origin: thoracolumbar fascia
:Insertion: teres tuberosity of the humerus
:Actions:
::antagonist to the brachiocephalic m.
::cranial fibers strap scapula to the chest
::retracts free limb and flexes shoulder joint
::draws trunk forward over the fixed limb
'''''Pectoral mm.'''''
'''''Pectoral mm.''''':
:Innervated by: brachial plexus
::superficial pectoral m. - ventral branches of cervical spinal nerves 7 and 8 (Evans and de Lahunta's Guide to the Dissection of the Dog, 8th ed.)
::deep pectoral m. - caudal pectoral nerves, cervical spinal nerve 8, and thoracic nerve 1 (Evans and de Lahunta's Guide to the Dissection of the Dog, 8th ed.)
'''''Serratis ventralis'''''
:Two superficial parts, cranial and caudal
:Origin: cranial sternum
:Insertion:
::cranial ('''descending'''): crest of the humerus distal to the deltoid tuberosity
::caudal ('''transverse'''): covers elbow joint to insert on the medial fascia of the forearm
:Action: adduct the forelimb, assist in protraction and retraction
'''''Rhomboids'''''
:One deep part ('''pectoralis profundus'''), with cranial and caudal parts
:Origin: ventral sternum and adjacent cartilage
:Insertions:
::cranial (subclavius): supraspinatus m.
::caudal (pectoralis ascendens): lesser tubercle of the humerus
:Actions:
::slinging trunk between forelimbs
::may also retract free limbs
::draw trunk forward when limb is fixed
'''''Serratis ventralis''''':
:Innervated by: branch of brachial plexus
:Origin: C4 to 10th rib
:Insertion: medial scapula and scapular cartilage
:Action:
::supporting the weight of the trunk reinforced by strong fascia
::cervical portion can retract the limb
::caudal portion can advance the limb
'''''Rhomboids''''':
:Innervated by: brachial plexus, although in some species, dorsal spinal nerves can innervate
:Origin: median connective tissue from poll to withers, lying deep to the trapezius
:Insertion: dorsal border and adjacent scapula
:Action: retracting the limb, may also raise limb
===Intrinsic Musculature===
===Intrinsic Musculature===
====Muscles of the Shoulder====
====Muscles of the Shoulder====
These muscles are grouped:
These muscles are grouped:
Lateral:'''Supraspinatus ''' and '''Infraspinatus''',
:Innervated by: Suprascapular n. of the brachial plexus
:Origin: the fossae of the scapula
:Insertion: both tubercles of the humerus
:Action: brace the shoulder
:Clinical significance: bursa between the tendon of the infraspinatus and lateral tubercle of the humerus can be the site of inflammation
Medial:
'''Subscapularis''':
:Innervated by: Subscapular n. from the brachial plexus
:Origin: Deep surface of the scapula
:Insertion: medial tubercle of the humerus
:Action: braces medial shoulder joint, potential adductor
'''Coracobrachialis''':
:Innervated by: Musculocutaneous n. of the brachial plexus
:Origin: medial supraglenoid tubercle
:Insertion: proximal shaft of the humerus
:Action: fixator
Caudal (Flexors):
:Innervated by: Axillary n. of the brachial plexus
:'''Deltoids'''
::Origin: caudal border and spine of the scapula, one head in the horse and two in species with an acromion (site of second origin)
::Insertion: deltoid tuberosity on the humerus
:'''Teres Major'''
::Origin: dorsal part of the caudal scapula
::Insertion: teres tuberosity midway down humerus
:'''Teres Minor'''
There are no defined extensors of the shoulder. Those involved (brachiocephalic m., biceps brachii, supraspinatus, and ascending pectorals) have other, more primary roles.
====Muscles of the Elbow====
====Muscles of the Elbow====
''Extensors'': Radial n. from the brachial plexus
''Extensors'':
:Innervated by: Radial n. from the brachial plexus
:'''Triceps brachii''': Three heads, four in the dog
::Long head: caudal margin of the scapula
::Lateral, medial, and accessory heads: shaft of the humerus
::Insertion: olecranon, proteced by tricipital bursa against the bone and subcutaneous bursa against the skin
:'''Tensor fasciae antebrachii'''
::Overlies triceps extending from scapula to olecranon
:'''Anconeus'''
::Origin: distal humerus
::Insertion: lateral olecranon
''Flexors'':
:Innervated by: Musculocutaneous n. from the brachial plexus
:'''Biceps brachii'''
::Origin: supraglenoid tubercle of the scapula
::Insertion: medial tuberosity of proximal radius and adjacent ulna
::Runs through the intertubercular groove of the humerus
:'''Brachialis'''
::Origin: proximocaudal humerus
::Insertion: spirals to insert next to biceps
====Muscles of Supination and Pronation ====
====Muscles of Supination and Pronation ====
''Supinators'': Radial n.
''Supinators'':
:Innervated by: Radial n. from the brachial plexus
:'''Brachioradialis'''
::Origin: lateral epicondyle of the humerus
::Insertion: distal medial forearm within superficial fascia
::Prominent in the cat but nearly absent in the dog
:'''Supinator'''
::Deep to extensor muscles, passing from lateral humeral epicondyles to upper medial radius
''Pronators'':
:Innervated by: Median n. from the brachial plexus
:'''Pronator teres''': only functional in cat and dog
::Origin: medial epicondyle of the humerus
::Insertion: supinator
:'''Pronator quadratus''': only found in carnivores
::Origin: shaft of the ulna
::Insertion: shaft of the radius
====Muscles of the Carpal and Digital Joints====
====Muscles of the Carpal and Digital Joints====
''Extensors'':
:Innervated by: Radial n. from the brachial plexus
:Craniolateral position on the forearm
:Almost all originate from the lateral epicondyle of the humerus
:'''Extensor carpi radialis''': most medial, inserts on 2nd/3rd metacarpal bone
:'''Ulnaris lateralis''': most lateral, inserts on accessory carpal bone
:'''Extensor carpi obliquus''': aka '''abductor pollicis longus'''
::Origin: cranial radius
::Insertion: most medial metacarpal bone
:Last two may also serve in medial deviation of the paw
:'''Common Digital Extensor'''
::Insertion: extensor process of the distal phalanx of each digit
::Sends a medial branch to dew claw and medial digits in all but horse and cat
:'''Lateral Digital Extensor'''
::Insertion: dorsal proximal phalanx
''Flexors'':
:Innervated by: Median or Ulnar n. of the brachial plexus
:Caudal position on the forearm
:Originate from the caudal medial epicondyle of the humerus
:'''Flexor carpi radialis''': most medial, inserts on upper 2nd/3rd metacarpal bone
:'''Flexor carpi ulnaris''': most lateral, inserts on the accessory carpal bone
:'''Superficial Digital Flexor'''
::Branches according to the number of digis and inserts in proximal interphalangeal joint
:'''Deep Digital Flexor'''
::Passes through carpal canal before branching and continues to palmar distal phalanges
''Interosseus muscles''
:Support metacarpophalnageal joints
:Arise from palmar proximal metacarpal bones and insert on sesamoid bones within the joints, continued by ligaments to phalanges
==Vasculature of the Forelimb==
*'''[[Arteries of the Forelimb - Anatomy & Physiology|Arteries of the Forelimb]]'''
*'''[[Veins of the Forelimb - Anatomy & Physiology|Veins of the Forelimb]]'''
*'''[[Lymphatics of the Forelimb - Anatomy & Physiology|Lymphatics of the Forelimb]]'''
==Innervation of the Forelimb==
The nerves affecting the forelimb arise from spinal nerves C6 to T2 and pass through the '''brachial plexus'''.
'''Suprascapular Nerve'''
* Origin - cranial part of brachial plexus, C6 and C7
* Motor innervation - supraspinatus and infraspinatus
* Sensory innervation - none
* Route - out of the brachial plexus, laterally round the cranial aspect of the neck of the scapula
'''Subscapular Nerve'''
* Origin - cranial part of the brachial plexus, C6 and C7
* Motor innervation - subscapular muscle
* Sensory innervation - none
* Route - direct to muscle
'''Musculocutaneous Nerve'''
* Origin - middle part of the brachial plexus, C7 and C8 (sometimes C6)
* Motor innervation - Biceps brachii, brachialis, coracobrachialis
* Sensory innervation - dorsomedial aspect of forelimb
* Route - medial aspect of the limb, close to the median nerve
'''Axillary Nerve'''
* Origin - middle brachial plexus, C7 and C8
* Motor innervation - shoulder flexors, teres minor, deltoid
* Sensory innervation - dorso-lateral aspect of proximal limb
* Route - behind the shoulder joint
'''Radial Nerve'''
* Origin - caudal brachial plexus, C7 to T2
* Motor innervation - extensors of elbow, carpus and digits
* Sensory innervation - dog: craniolateral and medial forearm, horse: lateral forearm
* Route - through the triceps, around the humerus to the lateral aspect of the forearm
'''Median and Ulnar Nerves'''
* Origin - caudal brachial plexus, C8, T1 and T2
* Motor innervation - flexors of carpus and digits
* Sensory innervation - caudal aspect of the limb
* Route - along the medial aspect of the limb, the median forms branches to the musculocutaneous nerve
==Species Specifics==
==Species Specifics==
===[[Canine Forelimb - Anatomy & Physiology|Canine Forelimb]]===
===[[Canine Forelimb - Anatomy & Physiology|Canine Forelimb]]===
===[[Bovine Forelimb - Anatomy & Physiology|Bovine Forelimb]]===
===[[Bovine Forelimb - Anatomy & Physiology|Bovine Forelimb]]===
{{Template:Learning
|OVAM = [http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-forelimb-extrinsics-quicktime Muscle flashcards - extrinsic musculature of the canine forelimb]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-shoulder-quicktime Muscle flashcards - muscles of the canine shoulder]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-elbow-quicktime Muscle flashcards - muscles of the canine elbow]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-antebrachium-quicktime Muscle flashcards - muscles of canine antebrachium]
}}
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[[Category:Musculoskeletal System - Anatomy & Physiology]]
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