Herbivore Thorax

Osteology

• 18 pairs of ribs

• sternum (manubrium, body, cartilaginous xyphoid process)

Withers

• topographic landmark between the shoulder blades

• spinous processes of T2-8

Cutaneous muscles

• cutaneous trunci

• cutaneous omobrachialis (fused to cutaneous trunci cranially)

Extrinsic limb muscles

• pectorals (+subclavius)

• trapezius

• serratus ventralis

• latissimus dorsi

Transversus thoracis

• ventral floor of thoracic cavity

Epaxial muscle groups

• dorsal to transverse processes of thoracic vertebrae

• spinalis system

• multifidus system

• longissimus

Hypaxial muscles

• ventral to the transverse processes of thoracic vertebrae

• longus colli - ventral aspect of neck into thoracic inlet

Diaphragm

• caudal aspect of thoracic cavity

• aortic hiatus for passage of aorta, R azygous vein, & thoracic duct

• esophageal hiatus for passage of esophagus & vagal trunks

• foramen vena cava for passage of caudal vena cava

Pleura

• maintains negative pressure for breathing

• visceral + parietal (mediastinal, costal, diaphragmatic)

Cupula pleura

• extension of pleura past level of rib 1 into neck

Line of pleural reflection

• where the parietal pleura reflects off of the ribs and onto the diaphragm

• demarcates caudal extent of thoracic cavity

Tracheal bifurcation

• into principal bronchi

• between intercostal space 4-6

Left lung lobes

• cranial and caudal lobe

• cardiac notch between lobes at level of ribs 3-6

Right lung lobes

• cranial & caudal lobe

• cardiac notch between lobes at level of ribs 3-4

• accessory lobe on medial aspect

Basal border of lung

• caudal aspect of lung in normal/relaxed state

• at ventral aspect of rib 6, middle aspect of rib 11, and dorsal aspect of rib 16

Heart location

• in intercostal spaces 2-6

• more vertically positioned

• long axis caudoventral, left of midline

Puncta maxima

• points of maximum heart sounds

• pulmonary valve: low intercostal 3 (L)

• aortic valve: high intercostal 4 (L)

• left AV: low intercostal 5 (L)

• right AV: low intercostal 3-4 (R)

Principal blood flow (left)

• ascending aorta → L/R coronary artery (provide heart w/oxygenated blood)

• aortic arch → brachiocephalic trunk

• brachiocephalic trunk → R/L subclavian + bicarotid trunk

  • different from dog!!

Left subclavian branches

• costocervical trunk → dorsal scapular + supreme intercostal

• deep cervical

• vertebral

• internal thoracic

• superficial cervical

Bicarotid trunk branches

• L/R common carotids

Right subclavian branches

• costocervical trunk → deep cervical + dorsal scapular + supreme intercostal

• vertebral artery

• internal thoracic

• superficial cervical

Dorsal/descending aorta branches

• bronchoesophageal

• dorsal + ventral intercostals caudal to each rib (anastomotic ring)

Supreme intercostal artery

• gives rise to first 3 intercostal arteries

Thoracic veins

• pulmonary veins (carry oxygenated blood back to heart)

• cranial + caudal vena cava

• R azygous vein

  • dorsal intercostal veins insert on R azygous

Intervenous tubercle

• contraction directs blood down from atria to ventricle

Parasympathetic NS

• craniosacral origin

• CN X/vagus nerve → R/L dorsal & ventral branches → dorsal & ventral trunks

• recurrent laryngeal nerve

• cardiac nerves

Sympathetic NS

• thoracolumbar spinal cord origin

• ramus communicans → sympathetic trunk w/ganglia

• middle cervical ganglion + cervicothoracic ganglion connected via ansa subclavia

• vertebral nerve off of cervicothoracic ganglion

• travel up vagosympathetic trunk towards head

Vagosympathetic trunk

• mixed parasympathetic & sympathetic NS

• dorsal + ventral vagal trunks from R/L dorsal + ventral vagal branches

• enter esophagus @ esophageal hiatus

Phrenic nerve

• originate from cervical spinal nerves 4-6

• motor innervation to diaphragm

• not ANS

Lymphocenters

• cranial, middle, & caudal mediastinal

• tracheobronchial (dorsal to tracheal bifurcation)

• intercostals (inconstant)

• sternal