Muscle Origins, Insertions, Actions: Deep Thoracic Muscles

Transversus thoracis m.

Origin: Dorsolateral border of the sternum between the third and eighth rib Insertion: Costal cartilages near the junction of the ribs Action: Moves ribs

Intercostalis internus m.

Origin: From a caudal rib Insertion: To an adjacent cranial rib Action: Retracts the ribs

Intercostalis externus m.

Origin: From a cranial rib Insertion: To an adjacent caudal rib Action: Protracts the ribs

Serratus dorsalis cranialis m.

Origin: From the cervicothoracic middorsal fascia Insertion: On the outer surface of the first nine ribs Action: Draws the ribs cranially

Serratus dorsalis caudalis m.

Origin: From the lumbar middorsal fascia Insertion: Last four or five ribs Action: Draws the ribs caudally

Transversus costarum m.

Origin: From the side of the sternum Insertion: First rib and costal cartilage Action: Pulls the ribs cranially

Serratus ventralis m.

Origin: From the surface of the first nine or ten ribs and the transverse processes of the last five cervical vertebrae Insertion: Vertebral border of the scapula Action: Draws the scapula toward the thoracic wall and helps to support the scapula

Scalenous anterior, posterior, and medius m.

Origin: S. anterior m.-from the second and third ribs S. posterior m.-from the third or fourth ribs S. medius m.-from the sixth through the ninth ribs Insertion: Transverse processes of all cervical vertebrae Action: Bends the neck and pulls ribs cranially