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- Cervical part: Median fibrous raphe of the neck, from the 3rd cervical to 7th cervical vertebra.
- Thoracic part: From the supraspinous ligament and dorsal spines of 1‐9 thoracic vertebrae.
- Insertion: Scapular spine.
- Nerve supply: Dorsal branch of the accessory (cranial nerve [CN] XI) nerve.
- Action: Elevate and draw limb forward
Serratus ventralis muscle
- Cervical part: Transverse processes of the last 3 cervical vertebrae.
- Thoracic part: Lateral surface of the 1st eight ribs.Insertion: Serrated face of scapula.
- Nerve supply: Cervical part, by ventral branches of the last 3 cervical spinal nerves, thoracic part by the long thoracic nerve of the brachial plexus.
- Action: Passive support of the trunk, with both limbs planted on ground, thoracic part helps in inspiration; moves scapula forward and backward.
- Strap‐like muscle. The superficial cervical lymph node is medial to this muscle (in all species!).
- Origin: Wing of atlas.
- Insertion: Lower spine of scapula.
- Nerve supply: Accessory (CN XI) nerve.
- Action: Draws scapula forward.
- Rhomboideus capitis: Occipital bone of skull.
- Rhomboideus cervical part: Tendinous raphe of neck from the 3rd cervical to the 7th cervical vertebrae; and spines of 1‐3 thoracic vertebrae.
- Rhomboideus thoracic part: From spines of the 4th – 6th thoracic vertebrae.
- Nerve supply: Ventral branches of 3‐7 cervical and 1‐6 thoracic spinal nerves.
- Action: Elevate the limb, move scapula forward, backward and pull it close to trunk
Latissimus dorsi muscle
- Origin: From thoracodorsal fascia via an aponeurosis (and indirectly from the spinous processes of the last 7 thoracic through lumbar vertebrae), lateral surface of the last 2‐3 ribs.
- Insertion: Mainly to the teres tubercle on the medial shaft of the humerus.
- Nerve supply: Mainly the thoracodorsal nerve from the brachial plexus.
- Action: Draw the limb backwards, and flex the shoulder joint.
- Attachments: Distal part of the humeral crest, to the cranial half of the cervical fibrous raphe, and to the mastoid part of the skull.
- Nerve supply: The cleidobrachialis part is supplied by a nerve from the brachial plexus (brachiocephalicus), the cleidocephalicus is supplied by ventral branches of several cervical nerves as well as the accessory (CN XI) nerve (specifically to the cleidomastoid part).
- Note: The complex innervation of this muscle indicates that it is a muscle resulting from the fusion of various muscles during evolution.
- Action: To draw limb forward, acting bilaterally, can flex the neck, acting on one side, can turn the neck
Superficial pectoral muscle
- Origin: From the first 2 sternebrae and associated costal cartilages.
- Insertion: Crest of the major tubercle of the humerus.
- Nerve supply: Cranial pectoral nn.Action: Mainly adduction of limb.
Deep pectoral muscle
- Origin: From all the sternebrae.Insertion: Both greater and lesser tubercles of humerus.
- Nerve supply: Mainly caudal pectoral nerves.
- Action: Mainly adduction of limb, also helps to draw limb backwards, or pull the trunk forwards.
What is the midline raphe?
All the spinous processes of vertebrae give rise to deep fascia. This deep fascial sheet reaches the dorsal midline of the neck and trunk, and gives origin to muscles. The fibrous line on the dorsal aspect of the neck and trunk formed by this deep fascia is called the midline raphe.
What is an important clinical note on the external jugular vein?
To apply digital pressure over the venipuncture site to prevent hematoma formation. Chances of hematoma formation is quite high here because the external jugular vein is surrounded by loose superficial fascia.
Has 2 parts, occipital and mastoid parts. This muscle arises from the manubrium of the sternum, and attaches to the mastoid part of the skull, and the nuchal line of the occipital bone of the skull. The muscle essentially flexes the neck when acting bilaterally, or helps to turn the head to one side. The external jugular vein runs on lateral surface of the sterno‐occipital part of the muscle. The sternomastoid part of the muscle is deeper, and cannot be easily separated from the occipital part.
The sternohyoid muscle attaches from the manubrium of the sternum, and part of the 1st set of costal cartilages. It attaches to the basihyoid bone of the hyoid apparatus, and helps in swallowing.
Made up of deep fascia, and envelops the common carotid artery, internal jugular vein, vagosympathetic trunk, tracheal lymph duct, and the recurrent laryngeal nerve. The deep fascia of the carotid sheath is continuous with the mediastinal fascia of the thorax, and thus, any infection in the carotid sheath has a chance to get into the thorax and cause infections there.
- A large muscle, easy to palpate cranial to the spine of the scapula in a live animal.
- Origin: Supraspinous fossa, part of the spine of the scapula, and neck of scapula.
- Insertion: Major (greater) tubercle of humerus.
- Nerve supply: Suprascapular nerve.Action: Extension of shoulder.
- A large muscle that fills the infraspinous fossa, and can be palpated caudal to the scapular spine in a live animal.
- Origin: Infraspinous fossa, spine of scapula.
- Insertion: Lateral aspect of the greater tubercle of the humerus.
- Nerve supply: Suprascapular nerve.Action: Flexes (mainly) and may also extend the shoulder, and slight abduction of limb.
What muscle has a bursa associated with it?
Intraspinatus muscle. Bursitis of this structure may cause lameness of the shoulder.
- A minor muscle, not terribly important (but we describe it anyway for completeness). Its minor surgical importance is when a caudal approach to shoulder is attempted, the muscle has to be reflected from the joint capsule with which it is closely associated.
- Origin: Mainly from the Infraglenoid tubercle.
- Insertion: Along the tricipital line proximal to the deltoid tuberosity on the humerus.
- Nerve supply: Axillary nerve.
- Action: Flexion of shoulder.
- Has two parts, the spinous part and the acromial part. The acromial part is larger and covers the acromion. If the muscle is atrophied (from axillary nerve damage), the acromion becomes prominent in a live animal. Palpation of the acromial part is a good landmark for locating the shoulder joint. A needle is then inserted proximal to the greater tubercle of the humerus.
- Origin: Acromion and spine of the scapula.
- Insertion: Deltoid tuberosity.
- Nerve supply: Axillary nerve.
- Action: Mainly flexion of shoulder, may help in abduction of limb.
What muscle in the forearm does not exhibit a tendinous origin? What would this mean in surgery?
The deltoid muscle. The muscle fibers are attached by fibrous tissue to the acromion. In surgery to access the shoulder joint, an acromion osteotomy would have to be performed, reflecting the acromial part of the muscle. The closure requires that the surgeon wire the process to the spine, and healing take place.
- Very large muscle located medial to the scapula and hence not palpable.
- Origin: Subscapular fossa of scapula.
- Insertion: Lesser tubercle of humerus.
- Nerve supply: Subscapular and axillary nerves.
- Action: Minor adduction of limb, may help in flexion and/or extension, depending on the phase of motion that the limb is in when the muscle contracts.
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