Equine & Ruminent Thorax

1. What are the boundaries of the bony thorax in the equine species?

dorsally: thoracic vertebra
laterally: ribs
ventrally: sternum

2. What forms the withers anatomically?

dorsal spinous processes of T2-T8

3. How many ribs are present in the horse?


4. Identify the parts of the equine sternum.

(cranial -> caudal) manubrium, body, xiphoid process (cartilage)

5. Be able to identify the muscles of the thoracic wall presented in class.

-cutaneous trunci
-extrinsic mm of thoracic limb:

6. Which muscles are included in the equine pectoral muscles?

superficial pectoral: descending & transverse pectorals
deep (ascending) pectoral

7. Where is the scalenus muscle located in relation to the equine thorax?


8. Which neural structures are anatomically associated with the scalenus muscle of the horse?

brachial plexus

9. Which muscle is present inside the thoracic cavity on the ventral aspect of the vertebral bodies?

longus colli

10. Which muscle covers the sternum inside the thoracic cavity?

transversus thoracis

11. Regarding blood supply and innervation of the thoracic wall, where are the intercostal arteries and nerves located in relation to the ribs and intercostal space?

caudal side of ribs

12. What is the topographic location of the heart within the thorax?

Intercostal spaces 2-6, more vertical than dog

13. What is the position of the heart in regard to its axis in the equine thorax?

long axis directed caudoventrally to left of median plane

14. Be able to identify the surface and internal structures of the heart.


15. Identify the fossa ovalis; what is its name and function in the fetus?

RA: in Interatrial septum depression where cranial and caudal vena cavae join @ intravenous tubercle, it is caudal to that.
Fetus: foramen ovale- hole btw atria

16. What is the function of the trabecula septomarginalis (septomarginal band, moderator band)?

In RV, muscular strand from interventricular septum to RV free wall that allows perkinje fibers to deliver electrical charge short cut

17. What are the puncta maxima and their clinical significance? Where are they located topographically in the horse?

Left: pulmonary valve (3rd ICS-low), aortic valve (4th ICS-high), L. AV valve (5th ICS-low)
Right: R. AV valve (3rd-4th ICS-low)

18. Why is it anatomically difficult to auscult the pulmonic valve in the equine species?

The position of the forelimbs, specifically the large mass of the triceps muscle, limits access to heart sounds

19. What is the topographic relationship of the olecranon to the lateral thoracic wall?

5th ICS

20. Be able to trace blood flow through the cardiac and pulmonary circulation.


21.Trace the arterial flow from the aortic arch to the level of the axillary artery; include all branches encountered along the path.

aortic arch-> brachiocephalic trunk-> (R/L subclavian, bicarotid trunk)
-Left subclavian-> costocervical trunk, deep cervical, vertebral, superficial cervical, continuation of left subclavian--> axillary, internal thoracic
-Right subclavian-> costocervica

22.Whatis the origin of the common carotid arteries?

bicarotid trunk,

23. Identify the ligamentum arteriosum; what is its name and function in the fetus?

connective/fibrous tissue btw PT and aorta
Fetus: ductus arteriosus, open vessel btw pulmonary trunk and aorta

24.Identify the major veins of the heart.

cranial vena cava, caudal vena cava, right azygos, pulmonary vv

25. What is the regional function of the azygos vein? Where is it located?

on right side, intercostal veins drain into it and meet up with cranial vena cava

26. Understand the naming convention for identifying mediastinal lymph nodes.

cranial mediastinal= numerous, cranial to heart, surround esophagus and vessels
middle mediastinal
caudal mediastinal= between esophagus and aorta, cranial to diaphragm

27.Be able to identify the thymus if present.

cranial mediastinum, largest @ 2mo and regresses, little remains after 3 years

28. Describe the path of the vagus nerve through the neck and thoracic cavity.

originates in brain stem CN X comes down neck, combined with sympathetic fibers (=vagosympathetic trunk) enters thoracic inlet (vagus), gives of recurrent laryngeal @ aorta, dorsal & ventral branches @ base of heart, L/R dorsal/ventral branches meet to ma

29.Be able to identify the origin of the recurrent laryngeal nerve in the thoracic cavity.

origin: vagus n
left side: courses around the aortic arch
right side: courses around the right subclavian a

30. Understand how the vagus nerve divides near the base of the heart to continue through the thoracic cavity and into the abdominal cavity as it changes from vagal branches to vagal trunks.

left/right have dorsal/ventral branches which come together to form dorsal and ventral vagal trunks

31. Be able to identify the sympathetic trunk and associated sympathetic ganglia.

cranially near first few ribs running along longus colli mm laterally, enlarged potions =ganglia

32. What is the origin of the vertebral nerve; what is its functional significance?

origin: cervicothoracic ganglion
-sympathetic contribution to cervical spinal nn

33. Be able to classify neural structures in the thoracic cavity as sympathetic or parasympathetic in function.

sympathetic: sympathtic trunk & ganglion, ansa subclavia, vertebral nn
parasympathetic: vagus nn, cardiac nn, phrenic n, brachial plexus

34. What is the specific origin of the phrenic nerve?

C5-7, crosses sclaenus, enters thoracic inlet

35. What is the specific origin of the brachial plexus?

C6-8, T1-2 emerges btw parts of scalenus

36. Where is the tracheal bifurcation located topographically?


37. What is the relationship of the thoracic esophagus and trachea?

esophagus is dorsal to trachea

38. Which vessels provide the functional and the nutritional blood supply of the lungs?

functional: pulmonary arteries (L&R)
nutritional: bronchoesophageal a

39. Be able to identify all the lobes of the equine lungs.

Left: cranial & caudal
Right: cranial, caudal, & accessory

40. Where are the left and right cardiac notches located?

left: rib 3-6
right: rib 3-4

41. What and where is the basal border of the lung? (Refer back to question #18 & 19 for clinical significance of the anatomy)

the most caudal/ventral margin of the caudal lobes which extends from 6,11,16
-costochondral junction 6th rib
-middle of 11th rib
-dorsal part of 16th rib
ventral bd of auscultation of lung fields

42.Be able to classify or identify pleura based on its location.

visceral/pulmonary: on the lung
parietal (mediastinal, costal, diaphragmatic)

43.Be able to distinguish the difference between the costodiaphragmatic recess and the cupula pleurae.

costodiaphragmatic recess is the potential space btw costal and peripheral part of diaphragmatic pleura
cupula pleurae- outpouching of pleura on the medial side of the right 1st rib, extending several cm in the neck

44. What is the clinical significance of the cupula pleurae?

only on right side, can puncture and cause pneumothorax

45. What and where is the line of pleural reflection in the equine species?

reflection of the costal pleura onto the diaphragm. Follows a course from : Ribs 8-9 costochondral jnct, curves caudally & dorsally progressively further from costochondral junctions of succeeding ribs, rib 17 vertebral end; dividing line between thoracic

46. What is thoracocentesis and where is it performed?

inserting a needle in pleural cavity 7th ICS-low

47. Understand the extent of the doming of the equine diaphragm.

oblique angle, vertex at rib 6

48. Identify the natural openings in the diaphragm; which structures pass through each?

Aortic hiatus: aorta, azygos v, thoracic duct
Esophageal hiatus: esophagus, vagal trunks
Foramen venae cavae: caudal vena cava

1. What is the ossa cordis and where is it located?

bone of heart in ruminant supporting aortic valve

2. Which lobes are present in ruminant lungs?

Left lung: cranial lobe (cranial & caudal parts), caudal lobe
Right lung: cranial lobe (cranial & caudal parts), middle lobe, caudal lobe, accessory lobe

3. What is the tracheal bronchus and where is it located?

@ T3, supplies right cranial lobe

4. Which specific part of the lungs is supplied by the tracheal bronchus?

right cranial lobe