Chapter 1: Thorax, Shoulder and Neck
Skin the cranial left quarter of the cat by making a midventral incision from the level of the ear to the level of the umbilicus. Make a transverse incision to the left from the caudal end of the midventral incision to the dorsal midline. Make a second transverse incision to the left from the cranial end of the midventral incision, just caudal to the ear, to the dorsal midline. Make a third transverse incision to the left from the midventral incision down the forelimb to the wrist. Make a circular incision around the wrist and reflect the skin to the dorsal midline.
Examine the muscles on the dorsal surfaces. Clean the muscles to expose the directions of the fibers. Identify and isolate each muscle using blunt dissection, freeing each muscle from its origin to its insertion. Do not remove the muscles from their attachments.
On the dorsal surface identify the three divisions of the trapezius muscles. The spinotrapezius muscle originates from the spinous process of the fourth through the twelfth thoracic vertebrae and inserts on the spine of the scapula. The acromiotrapezius muscle lies cranial to the spinotrapezius and it arises from the spinous processes of the cervical and the first four thoracic vertebrae. It inserts on the spine and metacromion process of the scapula. The clavotrapezius muscle arises from the superior nuchal line of the skull and from the mid-dorsal line of the neck to the spine of the axis and inserts on the clavicle.
Identify the latissimus dorsi and omotransversarius muscles (levator scapulae ventralis). Separate the spinotrapezius from the underlying latissimus dorsi muscle. The latissimus dorsi muscle originates from the thoracolumbar fascia over the spinous processes of the fifth thoracic through the sixth lumbar vertebrae and inserts on the proximal end of the humerus. Isolate the latissimus dorsi muscle.Transect the latissimus dorsi muscle two inches from its insertion on the humerus and reflect it to its attachments. Clean and observe the thoracodorsal artery and nerve on the inner surface of the latissimus dorsi at its humeral end.
Identify the three divisions of the deltoid muscle. The clavobrachialis muscle (clavodeltoid) arises from the clavicle and inserts on the ulna. The acromiodeltoid muscle arises from the metacromion process of the scapula deep to the omotransversarius and inserts on the proximal end of the humerus. The spinodeltoid muscle arises from the spine of the scapula and inserts on the proximal end of the humerus.
Observe the cephalic vein caudal to the clavobrachialis. Dissect the caudal margin of the clavobrachialis and Isolate the axillary nerve as it enters the deep surface of the clavobrachialis just distal to the clavicle. Isolate the acromiodeltoid and spinodeltoid muscles as far as possible.
On the ventral surface, identify the superficial pectoral muscles. The pectoantebrachialis muscle originates from the manubrium. Isolate this muscle from the pectoralis major and trace it to its insertion on the ulna. Transect this muscle and reflect it to its attachments. The pectoralis major muscle has its origin on the first three sternebrae and inserts on the proximal two thirds of the humerus.
The deep pectoral muscle consists of the pectoralis minor and the xiphihumeralis . The pectoralis minor muscle arises from the body of the sternum and inserts on the proximal half of the humerus. The xiphihumeralis muscle arises from the xiphoid process and passes deep to the pectoralis minor to insert on the proximal end of the humerus. Separate the pectoral muscles so that their attachments can be seen.
The clavobrachialis muscle lies cranial to the pectoral muscles. It arises from the clavicle and inserts on the ulna. Palpate the clavicle located medial to the greatest tubercle of the humerus. The clavotrapezius muscle arises from the superior nuchal line of the skull and from the mid-dorsal line of the neck to the caudal end of the axis and inserts on the clavicle. Dissect the cranial margin of the clavobrachialis and the clavotrapezius.
Displace the pectoral muscles cranially and observe the fan shaped serratus ventralis muscle . The serratus ventralis muscle arises from the last five cervical vertebrae and the first nine ribs and inserts on the vertebral border of the scapula. Identify the long thoracic nerve along its lateral surface.
the three scaleni muscles on the thoracic wall deep to the pectorals.
They arise from the cervical vertebrae and insert on ribs one through nine.
Medial to the scaleni identify the small rectus thoracis muscle and the cranial
portions of the rectus abdominis muscle. The rectus thoracis arises from the
sternum and inserts on the first rib.
In the neck, observe the external jugular vein on the medial border of the clavotrapezius muscle as it crosses the sternomastoid muscle superficially. Dissect the medial border of the clavotrapezius muscle and Isolate the sternomastoid muscle.
The sternomastoid muscle arises from the manubrium of the sternum and inserts on the mastoid process and the nuchal line of the skull. Identify the cleidomastoid muscle deep to the sternomastoid and the clavotrapezius. It arises from the clavicle and inserts on the mastoid process of the skull. The omotransversarius muscle may be seen dorsal to the cleidomastoid.
Locate the sternohyoid muscle originating from the manubrium and inserting on the hyoid bone in the ventral midline of the neck. The sternothyroid muscle is located deep and lateral to the sternohyoid. It originates on the manubrium and inserts on the thyroid cartilage of the larynx. Isolate these muscles from their origin to their insertion.