WESLEY D. ANDERSON 
769 
of certain artificial heart devices which must 
be implanted in the cranial portion of the tho- 
rax. The sheep does however have many mor- 
phological advantages in cardiovascular re- 
search; unfortunately, the small thoracic inlet 
is one of its disadvantages. 
The bony thorax of man on the other hand 
(Figure 2) is more conical in shape and in the 
adult male the transverse diameter averages 
12.5 cm and its anteroposterior diameter meas- 
ures 6.0 cm.- 
Trachea, Bronchi and Associated Structures 
The bifurcation of the trachea into right and 
left principal bronchi occurs at the sixth tho- 
racic vertebra in sheep and the seventh thoracic 
vertebra in the living human being (Figures 3 
and 4). The right principal bronchus has a 
wider diameter than the left bronchus in sheep, 
calf and man, and the left principal bronchus in 
these species is larger and arises by more of an 
acute angle than the right (Figures 5 and 6). 
There is also similarity in position of the aorta, 
Figure 2. — Anterior view of human bony thorax. 
Reproduced by permission from: W. Henry Hollinshead. TEXTBOOK OF ANATOMY (ed. 2). Copyright (1967). Hoeber Medical Di- 
vision — Harper & Row., New York. 
