Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Thorax and Heart of the Cat (Felis catus)

Photos and Text by Adam Harstsone-Rose

Introduction:

The thoracic organs (lungs and heart), nerves, and vessels of the cat are much like those of the human, though the orientation of the cat’s thoracic organs differs mostly due to cats’ quadrupedality [1].

Dissection Technique:

Begin the dissection by removing all skin and as much musculature as possible from the anterior of the chest and neck.  Make a transverse incision just caudal to the xiphoid process (of the sternum).  Take care to cut into the thoracic cavity cranial to the diaphragm and avoid the abdominal cavity, which is caudal to the diaphragm.  Cut through the ribs (with a strong pair of scissors or shears) from the transverse cut you just made, along the side of the animal (in the coronal plane) all the way to the neck.  Repeat this cut along the other side.

Reflect the newly freed anterior thoracic wall cranially.  The parietal pleura (the outer layer of the lung covering) may adhere to the thoracic wall.  Remove it from either the ribs or the lungs, but take care not to damage the organs.

The lungs, heart (wrapped in pericardium), thoracic vessels and nerves should all be visible, as should the thymus gland, a mass of pinkish glandular tissue cranial to the heart along the midline.  Observe these structures as they are in the body, and then remove the heart by carefully piercing and reflecting the pericardium and severing the great vessels as close to the heart as possible.  Note that the heart is centered in the thorax and that the ventricles are oriented ventral to the atria.  This is different than the human state, which many anatomists are most familiar with.  Remove the lungs by severing them at their root, close to the mediastinum (the central mass of nerves, vessels and connective tissues between the lungs).  Note that, in the cat, the left lung has three lobes and the right lung has four.  The three cranial lobes of the right lung are very symmetrical with those of the left lung, and its fourth lobe is caudal to the heart along the midline and rests on the diaphragm.

Clean the connective tissue along the vessels, nerves and esophagus in the thorax and neck.  Do this carefully as these structures can be fairly delicate.

The heart:

The great vessels enter and exit the heart dorsally and it hangs with its apex pointing ventrally.

Table 1.  Great Vessels of the Heart.

Blood Flow:

The heart is the body’s blood pump.  Blood flows into the right atrium of the heart from the precaval vein (“superior vena cava” of humans), from the upper limbs, head, neck and part of the thorax, and the postcaval vein (a.k.a. the “inferior vena cava” of humans) from the abdomen, lower limbs and the rest of the body wall.  From the right atrium it is pumped into the right ventricle.  The right ventricle pumps it out into the lungs via the pulmonary artery (the only artery in the adult mammal with predominantly deoxygenated blood).  The blood then returns to the heart’s left atrium via the pulmonary vein (the only vein in the adult mammal with predominantly oxygenated blood) where it is pumped into the left ventricle.  The left ventricle then forces the blood at high pressure out of the heart and to the rest of the body via the aorta.

Heart Anatomy:

The atria are thin, lined sacks predominantly composed of tissue from the developing great vessels.  The atrial caverns are continuous with the auricles, sac-like appendages that wrap around the craniodorsal surface of the heart.  Between the atria, on the atrial septum, is the closed oval foramen, or fossa ovalis [2].  It and the closed arterial duct, the ligamentum arteriosum, are the remnants of two important shunts that protected the developing fetal lungs from high blood pressure before they were needed for oxygenation.  These shunts close at or shortly after birth.  The ventricles, unlike the thin atria, are tough muscular pumps that pumps blood to the lungs and body.  They are lined with trabeculae carnae, strap-like muscles that attach to the atrioventricular valves via the string-like chordae tendinae to keep the valves from flowing in the wrong direction when the blood is being forced out of the heart.  At the most proximal end of the aorta, just as it leaves the heart, are ostia of the coronary arteries.  Though the heart can get some of its oxygen from the blood within it, most of the oxygen that feeds the thick heart muscles comes from the blood pumped through these arteries that wind around the heart between its four chambers.

Arterial Blood Flow:

As in all vertebrates, blood leaves the heart through the aorta, which immediately gives off a right brachiocephalic artery and then a left common carotid artery and left subclavian artery.  The right brachiocephalic trunk splits into right common carotid and right subclavian arteries.  One major difference between the quadrupedal cat and the bipedal human arrangement is that in the cat there is no real “aortic arch.”  Instead the aorta is fairly straight and runs caudally along the left side of the vertebral bodies down through the diaphragm, and the heart is suspended ventral to it.

Venous Blood Flow:

Blood flows into the right atrium of the heart from one large craniad vein (precaval vein) and another caudad vein (postcaval vein).  The precaval vein is the combination of left and right brachiocephalic veins, which themselves are the combination of the jugular and subclavian veins of their respective sides.

Discussion:

If you have dissected another mammal, then this dissection should be rather straightforward and familiar.  The cat differs only in very few ways from other higher mammals, and these differences are mainly in the orientation and relative size of structures, and the number of lobes of the lungs (though even these are similar to many other mammals) [1].  Thus, from a comparative mammalian stand point the cat is fairly typical.

References:

1. Vollmerhaus, B., Roos, H., Matis, U., Veith, G. & Tassani-Prell, M. 1999. The specific anatomy and function of the thorax of the domestic cat. Tierarztliche Praxis Ausgabe Kleintiere Heimtiere. 27:365-370

2.  Macdonald, A. A. & Johnstone, M. 1995. Comparative anatomy of the cardiac foramen ovale in cats (Felidae), dogs (Canidae), bears (Ursidae) and Hyaenas (Hyaenidae). J. of Anat. 186: 235-243