• 1st rib, longus coli m, & manubrium

• Subclavians, carotids, jugulars, superficial cervicals

• Ventral branches T1-2 to brachial plexus, vagosympathetic trunk, phrenic nerve

• Esophagus & trachea
  

• Thoracic inlet

• Diaphragm

• Esophageal hiatus, aortic hiatus, & caval foramen

• Pleura overlying endothoracic fascia

• Muscular
• Tendinous

• Peripherally located
• Attached to:
  • Costae
  • Ventral surface of lumbar vertebral bodies, via crura of the diaphragm
    • Thoracic aorta passes between crura to become abdominal aorta
    • Lumbocostal arch (potential space b/w dorsal body wall & crura)
      • Major splanchnic nerve passes from thoracic cavity into abdominal cavity

• Centrally located
• Openings:
  • Esophagus & caudal vena cava, aorta

• Diaphragmatic
• Costal
• Mediastinal

• Pulmonary
• Epicardial

• Nothing

• Left lobes
  • Cranial
    
    • Subdivided in ruminants, pig, & dog
  • Caudal
• Right lobes
  • Cranial
    • Subdivided in ruminants
    • Right cranial-cranial portion extends to the left, in front of the heart into cupula of pleura
  • Horse has no middle lobe
  • Accessory
• Distinct lobulation in cows but less in small ruminants

• Both sides, b/w intercostal spaces 3 & 4

• Visceral (pulmonary) pleura

• Pulmonary aa. (branches of pulmonary trunk)
• Pulmonary vv.
• Bronchaial aa. from bronchoessphageal a.
• Lymphatics

• Tracheal bifurcation: dorsal to the base of the heart

• Right principal
  • Cranial lobar bronchus
    • Ruminants & pigs- originated directly from the trachea (tracheal bronchus)
  • Caudal lobar bronchus
  • Middle lobar bronchus (not in horse)
  • Accessory lobar bronchus
• Left principal
  
  • Cranial & caudal lobar bronchus

• Medial to the olecranon, Left intercostal spaces 3, 4, & 5

• Medail to the olecranon, right intercostal spaces 3 & 4

• Azygous vein
  • Right azygous dorsolateral to aorta
• Cranial & caudal vena cava

• Pulmonary arteries
  • Right & left pulmonary arteries

• Ascending
  • Right & left coronary arteries
• Arch
  • Brachiocephalic trunk
    • Left subcalvian artery, bicarotid trunk, right subclavian artery
• Descending
  • Dorsal intercostal aa.
  • Bronchoesophageal a.

• Phrenic
  • Ventral branches of C5-7
  • Comes in throacic inlet back to diaphragm
• Vagus (right & left)
  • Cardiac nerves
  • Recurrent laryngeal nerve
    • On left side, branches off the vagus & swings around the heart up the neck to the larynx
    • On right side comes around subclavian
  • Dorsal & ventral branches
    • At bifurcation of trachea, past the heart, the branches will join to make dorsal vagal trunk & ventral vagal trunk
  • Dorsal & ventral vagal trunks (right & left)
• Sympathetic trunk
  • Ganglia
    • Cervicothoracic & sympathetic trunk
    • Nerves
      • Rami communicantes, thoracic splanchnic, cardiac, ansa subcalvia

• Intercostal lnn.
• Mediastinal lymph center
  • Cranial mediastinal lnn.
  • Middle mediastinal lnn.
  • Caudal mediastinal lnn. (large & many)
    • b/w esophagus & aorta
• Pulmonary lnn.
  • Along proximal bronchi
• Tracheobronchial lnn. (right, left, & middle)
  • Tracheal bifurfaction (right above the heart)
• Thoracic duct: Cisterna chyli to venous angle
  • Takes lymph from cd. diagphragm to venous angle
  • Crosses to left side at base of heart

• Cranial mediastinum is cranial to heart
• Middle is in the middle (contains the heart, great vessels, trachea, & esophagus- all covered by mediastinal pleura)
• Caudal is caudal to the heart

• Branch off the vagus
• Right branch leaves the right vagus at the level of the 1st rib & loops around a branch of the subclavian artery & then continues to the neck
  • Tends to be the smaller branch
• Left branch arises farther caudally near the base of the aortic arch & passes from lateral to medial around the arch of the aorta to continue to the neck
  • Has farther to go, so its longer

• The position is the same
• The neurovascular bundle runs caudal along each rib
• The order from cranially to caudally is: artery, vein, then nerve

• Primary bronchi are air passageways to each lung, originating at the tracheal bifurcation.
• Lobar bronchi are the secondary bronchi off the primary bronchus for that lung.  Each secondary leads to a lobe of the lung.

• A secondary bronchus straight off the trachea.
• It is the right cranial lobar bronchus in ruminants & pigs.

• The left lung has cranial & caudal lobes in all species
  • Its partially split into cranial & caudal parts in larger ruminants, pigs, & dogs.
• The right lung as cranial, caudal, middle, & accessory lobes.
  • Accessory lobe lies on midline
  • Ruminants: cranial lobe is subdivided into cranial & caudal parts, that extend to the left in front of the heart & into the cupula of the mediastinum.
  • Horses do not have a middle lobe
• Cow: heavily lobulated with connective tissue
  • Each lobe has its own secondary bronchus off of the primary bronchus for that lung
• Pigs & ruminants: cranial lobar bronchus comes off the trachea

• Covered by pulmonary pleura
• Pulmonary ligaments are the reflections of the pleura b/w the mediastinal pleura & the right & left caudal lungs
• Plica vena cava is the connecting pleura b/w the caudal vena cava & the diaphragm, pericardial sac, & floor of the thorax

• Horse, which lacks a middle lobe for the right lung

• Pulmonary aa. & vv. carry blood back & forth b/w heart & lungs
• Bronchial a. & bronchoesophogeal a. carry blood for nutrition to the cranial portion of the lung

• Tracheobronchial lnn. lie along the bifurcation of the trachea
  • Left tracheobronchial lnn. is present in all species
  • Others also have middle & right ones
• Also pulmonary lnn. at the primary bronchii

• Cranial & left aortic sinuses b/w the cusps of the aortic valve give rise to the right & left coronary arteries, respecitvely.
• Right coronary artery courses cranially under the right atrium & into the right coronary groove.
  • In the horse, it then gives rise to the subsinuosal interventricular groove (b/w ventricles on the caudal side of heart)
• Left coronary artery courses under the left atrium & branches into the paraconal interventricular branch that runs in the paraconal interventricular groove (b/w ventricles on cranial side of heart) & circumflex branch, that continues in the coronary groove to the right side of the heart
  • In the dog, this vessel gives rise to the subsinuosal interventricular branch
• The circumflex branch & right coronary artery may anastomose.

• An anastomosis b/w the right coronary artery & the circumflex branch

• Right & left coronary arteries

• Brachiocephalic trunk
  • Left subclavian a. - supplies neck, cranial thoracic wall, & left limb
  • Vertebral a. - courses cranially & through transverse canal of cervical vertebrae
  • Costocervical trunk - arises near vertebral a.
  • Superficial cervical a. - arises near thoracic inlet & runs on superficial neck from shoulder
  • Internal thoracic a. - arises opposite the superficial cervical a. & courses along the floor of the thorax
  • Bicarotid trunk
  • Right subclavian a. - supplies neck, cranial thoracic wall, & right limb
  • Vertebral a. - courses cranially through the transverse canal of cervical vertebrae
  • Costocervical trunk - arises near vertebral a.
  • Superficial cervical a.
  • Internal thoracic a.

• Dorsal intercostal aa.
• Brochesophageal a.

• Left side:
  • Intercostal spaces 3, 4, & 5 fo pulmonic, aortic, and left AV valve respectively
• Right side:
  • Intercostal spaces 3 & 4 for the right AV valve

• Fibrous pericardium- fibrous sac surrounding the heart & serous pericardium
• Serous pericardium- potential space b/w the two layers is called the pericardial cavity
  • Parietal layer of serous pericardium- lines inner surface of the fibrous pericardium
  • Epicardium- visceral layer of serous pericardium

• Right azygous v. enters b/w caval openings or joins cranial vena cava, blood deflected by intervenous tubercle ventrally to AV ostium --> AV valve --> right ventricle --> passes trabecula septomarginalis, trabeculae carnae, conus arteriosus --> pulmonary valve --> pulmonary trunk --> right or left pulmonary artery --> lungs --> pulmonary veins --> craniosinistral, craniodextral, caudal sites of left atrium --> left AV valve --> left ventricle, apex --> aortic valve --> aorta

* Coronary sinus in right atrium