Fox heart and thorax
Photo and Text: Nick Zolkowski and Elizabeth Farrell
The heart functions as the pump of the circulatory system. Deoxygenated blood returns from the body via the anterior and posterior vena cava and enters the right atrium. It then passes to the right ventricle, and is pumped through the pulmonary artery to the lungs, where it becomes oxygenated. Returning through the pulmonary vein to the left atrium, it then passes to the left ventricle. Here, in the most muscular chamber of the heart, the oxygenated blood is finally pumped through the largest artery in the body, the aorta, to the rest of the body.
At the beginning of the dissection we cut through the costal region with bone shears. We then reflected the rib cage and removed layers of pleura to expose the thoracic cavity. This opened a view from mid-chest to the diaphragm, a semispherical muscle which, due to preservation, was stiff and hard. The heart and lungs are the most noticeable structures in the cavity, with the heart surrounded by the lobes of the two lungs. The lungs are brown, smooth, and relatively thick, with the right lung slightly larger in size. There are seven lobes total: both the right and left lungs have three lobes flanking the sides (cranial, middle and caudal), and the right lung has an accessory lobe dorsal and caudal to the heart. The number and positioning of the lungs are variable across mammalian species, although the functional significance of such variation is disputed. One theory speculates that the placement of the lungs in canids may play a role in locomotion by stabilizing the rib cage and contributing to locomotor-respiratory integration [1].
Running dorsal to the lungs are the esophagus and trachea. We distinguished the trachea from the smoother esophagus by the cartilaginous rings embedded in the tissue, which function to keep the passageway open.
The heart is slightly to the left of the midline, with the aorta and anterior vena cava running parallel to the spine. The tip of the right ventricle is angled ventrally. Before removal, the left ventricle and part of the right ventricle were visible. However, we were able to rotate the heart about the aorta and vena cava to see the other aspects. We removed the heart by cutting through the cranial and caudal vena cava and the aorta. In the ventral view, the fox's right and left atria are superior to the right and left ventricles, respectively. However, the left atrium is significantly smaller in size than the right atrium. Additionally, both atria are small in comparison to the ventricles. In the dorsal view, the cranial and caudal vena cava and aorta are visible. The heart has a cranio-caudal length of 10 cm. and a width of 7 cm., and fits in the palm of a human hand.
Openings in the heart from the pulmonary arteries and veins were also seen. We made incisions in to the walls of the right atrium and right ventricle. This allowed partial visibility into the interiors of the chambers. Despite widening the incision, there was not enough light to observe any internal structures. We did, however, locate the bicuspid, tricuspid, aortic, and pulmonary valves. The tricuspid valve lies between the right atrium and right ventricle, and has three cusps. The bicuspid valve, correspondingly, has two cusps and lies between the left atrium and left ventricle. The aortic valve and pulmonary valve each have three semi-lunar cusps, with the aortic valve lying between the left ventricle and the aorta and the pulmonary valve lying between the right ventricle and pulmonary artery.
1. Bramble, D.M. and Jenkins F.A. Jr., 1993. Mammalian locomotor-respiratory
integration: implications for diaphragmatic and pulmonary design. Science. 262:
235-40