774 
ANATOMY AND PATHOLOGY 
Figure 8. — Some variations in the branches of human aorta, a is the expected pattern; 
in b the left common carotid shares a short common trunk with the brachiocephalic; 
in c and in d the left vertebral artery arises directly from the aorta; in e there is a 
short left brachiocephalic trunk; and in / the right subclavian arises anomalously 
and passes behind trachea and esophagus. 
Reproduced by permission from: W. Henry Hollinshead, TEXTBOOK OF ANATOMY (ed. 2). Copy- 
right (1967). Hoeber Medical Division — Harper & Row., New York. 
have a distinct vessel demarcating it. The apex 
of the sheep heart is somewhat pointed and 
projects obliquely downward and toward the 
diaphragm near the sixth intercostal space, 
while the apex of the human heart projects 
about eight cm to the left at the fifth inter- 
costal space. The atria and origin of the great 
vessels form the base of the heart in the sheep 
while the sternocostal surface is formed prin- 
cipally by the left ventricle and by a portion 
of the right ventricle. In this sulcus dividing the 
two ventricles, the cranial interventricular 
branch of the left coronary artery descends 
while the great cardiac vein ascends and turns 
to the left to enter the coronary sulcus where 
it will become the coronary sinus and empty 
into the right atrium. 
Comparison to Man 
The mean distance from the base to apex of 
the sheep heart is generally 12-13 cm, while 
the circumference taken at the coronary groove 
is approximately 29 cm. The distance from base 
to apex of the sheep heart is remarkably similar 
to base-apical distance in man of 12.5 cm.^ The 
mean weight in a study involving 54 sheep 
hearts was 222.0 gms, while the average weight 
of the human female heart is 255 gms and the 
human male heart 312 gms.^ 
Autonomic Innervation of Heart and 
Associated Structures 
In quadrupeds as in man two sets of nerves 
reach the heart: one from the sympathetic 
trunk and one from the vagi. The right and left 
vagal nerves enter the thorax of the sheep on 
the lateral surface of the esophagus, cross be- 
neath the subclavian artery and continue cau- 
dally parallel to the brachiocephalic trunk 
where they each give off cardiac branches (Fig- 
ures 12 and 13). On the left surface of the 
aorta, the left recurrent laryngeal nerve arises 
