Dissection 2.1 - Superficial Thorax

Dissection guide

Articulated Skeleton

• Costal groove: inferior border ribs 2-12

• Costal margin: inferior border of rib cage

• Sternum sections (superior → inferior)

  • Suprasternal notch → Manubrim → Sternalchondral ligamen → Body of sternum → Xiphoid process

Anterior Thoracic Wall

• Cephalic vein: located between deltoid and pectoralis major (in deltopectoral groove)

• Layer 1: Pectoralis major

  • 3 bony attachments: ribs, sternum, clavicle

  • Innervated by lateral pectoral n. (superior to medial pectoral n.)

• Layer 2: Pectoralis minor

  • Deep to pectoralis major

  • Innervated by medial pectoral n. (nerve pierces muscle and then enters pectoralis major)

• Layer 3: External intercostal muscles

  • Fibers slant inferiorly and medially

    • Collagen fibers have same orientation

  • Medial part → External intercostal membrane (thin stretched out external intercostal m.)

• Layer 4: Internal intercostal muscle

  • Lateral to sternum

  • Fibers slant inferiorly and laterally (perpendicular to external intercostal m.)

• Intercostal VAN located in costal groove

  • Ventral rami of first 11 thoracic spinal n. → 11 intercostal n.

  • Ventral ramus T12 → Subcostal n.

Dermatomes

• Cutaneous n. that innervate a region of skin

  • All SS cell bodies located in DRG of spinal n.

• Clinically relevant for herpes zoster

Skinning the Neck

• Layer 1: Platysma (embedded in superficial fascia)

  • SM innervated by cervical branch of CN VII

  • Other structures in the area include tributaries of anterior jugular v. and cutaneous branches of cervical plexus

  • Attaches onto the clavicle

• Layer 2: SCM (not covered in this dissection)

  • Attaches onto the clavicle

Clavicle Removal

• Clavicle is superficial to structures of the neck and thorax

• Sternoclavicular joint: Joint between sternum and clavicle

Bolded terms

Acromion process

• Flat, expanded projection at the outer end of the spine of the scapula (shoulder) and articulates with clavicle

Body of the sternum

• Part of sternum between manubrium and xiphoid process

  • Manubrium is superior to the body (manubirosternal joint aka sternal angle in between, contain intraarticular sternochondral ligament)

  • Xiphoid process is inferior to the body

Cephalic vein

• Located between deltoid and pectoralis major

• Cephalic v. → Axillary v. → Subclavian v. → Brachiocephalic v. → Superior vena cava → Right atrium

Clavicle

• Bone located superficial to structures of the neck and thorax but deep to muscles of the thorax

• Attachment for SCM and platysma at superior border

Corpus (body) of the mandible

• Section of mandible between mental protuberance and ramus

Costal cartilage

• Hyaline cartilage that connects the ribs to the sternum

  

Costal groove

• Groove located on the inferior border of ribs 2 to 12

• Formed by pulsations of the intercostal artery

• Holds the intercostal VAN

Costal margins

• Inferior border of the ribcage

Costochondral joint

• Short bar of costal cartilage located between the anterior end of the first rib

• Articulates with the manubrium of the sternum (sternochostal joint)

Dermatome

• Strip of skin innervated by dorsal and ventral cutaneous nerves from a single spinal nerve

External intercostal membrane

• The most medial part of external intercostal muscle that is a semi-transparent membrane (under which we can see internal intercostal muscles)

External intercostal muscle

• Seen lateral to the costochondral joint

• Muscle fibers point inferior-medially

• Elevate the ribs and expand the chest cavity

First rib

• Most superior rib

Genu/symphysis of the mandible

• The point of fusion where the two halves of the lower jaw (mandible) join together during development, forming a single bone

• Located in midline - near chin

Gonial angle

• Inferior angle of mandible (between body and rami)

Intercostal artery

• Runs in intercostal groove

• Subclavian a. → Costocervical trunk → Intercostal a.

Intercostal nerve

• Runs in intercostal groove

• Arises from ventral rami of 1st 11 thoracic spinal nerves

Intercostal vein

• Runs in intercostal groove

Internal intercostal muscle

• Located just lateral to the sternum and deep to external intercostal membrane

• Fibers run inferiorly and laterally

• Pulling the ribs downward and inward, effectively reducing the thoracic cavity volume and pushing air out of the lungs

Lateral pectoral nerve

• Supplies innervation to pectoralis major (located medially)

• Branch of lateral cord of brachial plexus

Manubrium

• Superior portion of sternum

Medial pectoral nerve

• Supplies innervation to pectoralis minor (located laterally - pierces into pectoralis minor and enters pectoralis major)

• Branch of medial cord of the brachial plexus

Pectoralis major

• Superficial muscle in thorax

• Innervated by medial and lateral pectoral nerves

Pectoralis minor

• Deep to pectoralis minor

• Innervated by medial pectoral nerve

Platysma

• Thin muscle embedded in the superficial fascia deep to the skin

• Innervated by CN VII

Ribs

Second rib

Sternocostal joint

• Joint between manubrium of the sternum and the costal cartilage which joins the anterior ends of the 1st rib

Sternum

Subcostal nerve

• The ventral ramus of T12 that lies below the 12th rib

Suprasternal/jugular notch

• Notch at the superior margin of the manubrium

Trapezius muscle

• Large diamond shape muscle that spans the back

Ventral rami

• Carry all 3 fiber types to the ventral side of the body (SM, SS, VS)

Xiphoid process

• Inferior portion of the sternum