WESLEY D. ANDERSON 
773 
pericardial ligament. The sternocostal surface 
of the sheep heart is partially covered by the 
right and left cranial lobes and right middle 
lobe of the lung (Figure 10), and in the young, 
the heart is also partially covered by the tho- 
racic lobe of the thymus. The fibrous pericar- 
dium is coated by a layer of mediastinal pleura 
and is crossed near the base of the heart by 
the right and left phrenic nerves. Cranial to 
the heart in the sheep and calf, the mediastinum 
encloses considerable amounts of adipose tissue 
as well as the thoracic lobe of the thymus. 
External Anatomy 
The surface of the sheep heart, unlike the 
surface of the human heart, is characterized 
by abundant amounts of epicardial fat espe- 
cially prominent in all sulci. The right or acute 
margin is demarcated by the right marginal 
artery while the left or obtuse margin does not 
Brachiocephalic trunk 
Figure 7. — Aortic arch of the sheep. 
