Thoracic Topography

Question 1

how many pairs of ribs do dogs, cows, and horses have?

Answer 1

dogs and cows have 13 rows of paired ribs, so 26 total
horses have 18 rows of paired ribs, so 36 total

Question 2

describe the musculature of the thoracic wall (5)

Answer 2

1. serratus dorsalis cranialis and caudalis: superficial and pull ribs cranially or caudally
2. serratus ventralis cervicis and thoracic lie more ventrally
3. external abdominal oblique muscles lie deep to serratus ventralis
4. external intercostals lie in the spaces between the ribs
5. rectus abdominis muscle is most medial

Question 3

describe pleura and ID its specific divisions

Answer 3

the pleura lines the thoracic cavity and its organs; includes
1. serous membrane: lines thoracic wall, heart, lungs, and forms mediastinum/visceral pleura; adheres directly to the organs
2. pleural space: potential space containing a few ml of fluid that keeps the lungs adhered to the thoracic wall
3. parietal pleura: further divided into costal (attached to ribs), mediastinal (division between left and right side of mediastinum), and diaphragmatic (attached to diaphragm)

Question 4

which structures populate the cranial (precardiac) mediastinum? (9)

Answer 4

1. trachea
2. esophagus
3. cranial vena cava
4. brachiocephalic trunk
5. lymph nodes
6. thymus
7. vagus nerve
8. cardiac nerves
9. phrenic nerve

Question 5

which structures populate the middle (cardiac) mediastinum? (6)

Answer 5

1. root of lungs
2. esophagus
3. lymph nodes
4. vagus nerve
5. phrenic nerve
6. heart

Question 6

which structures populate the caudal (postcardiac) mediastinum? (5)

Answer 6

1. aorta
2. azygos vein (right vein only in equines and dogs, right and left veins in cows)
3. esophagus
4. caudal vena cava
5. vagus nerve

Question 7

describe cupula pleurae and the clinical significance

Answer 7

where the pleura extends approx 2 inches beyond the first rib (thoracic inlet) on the right side of the thorax; is exposed to injury in equines and can be perforated, leading to pleural cavity infection, putting the lungs and heart at risk

Question 8

describe the line of pleural reflection and ID its caudal extent

Answer 8

the line of pleural reflection is the caudal extent of the pleura; the caudal border of the lungs is cranial to this line, so you can access the pleural cavity in the space between the caudal border of the lungs and the line of pleural reflection

Question 9

describe the dome of the diaphragm and ID its cranial extent

Answer 9

formed by the abdominal cavity squishing up into thorax

Question 10

define puncta maxima and ID their location in dog, horse, and cow

Answer 10

the place where you listen to the heart valves on the thorax
left AV/mitral valve
horse and dog: low in the left 5th ICS
cow: low in the left 4th ICS

aortic valve:
horse and cow and dog: high in the left 4th ICS

pulmonic valve:
horse and cow and dog: low in the left 3rd ICS

Right AV/tricuspid valve:
horse and dog: low in the right 4th ICS
cow: low in the right 3rd or 4th ICS

Question 11

where are the caudal mediastinal lymph nodes in cattle and how might inflammation or these nodes affect the digestive tract?

Answer 11

the caudal mediastinal lymph nodes in ruminants lie near the dorsal vagal trunks, so if these LNs are inflamed, they can compress this trunk; the vagus nerve innervates many abdominal organs and this is why thoracic inflammation can lead to GI issues if these nerves are compressed by caudal mediastinal LNs