WESLEY D. ANDERSON 
783 
Valvules of 
pulmonary valve 
Right 
Cranial (anterior) 
Left 
Right coronary a. 
Cranial (ant.) interventricular a 
Left coronary a 
Left circumflex a 
r Cranial (ant.) 
Cusps of J 
mitral valve [^caudal (post.) 
Valvules of 
aortic valve 
Adipose tissue 
Caudal (posterior) 
Cranial (ant.) 
Caudal (post.) 
Septal 
Cut edge of right atrium 
Cut edge of left atrium 
> 
Cusps of 
tricuspid 
valve 
Figure 20. — Dorsal (superior) view of semilunar and atrioventricular valves of sheep heart. 
spaces are supplied by spinal branches from 
the aortic intercostal arteries (Figure 28) 
which anastomose with intercostal branches of 
the internal thoracic arteries. Each aortic 
(dorsal) intercostal artery also has a spinal 
branch which enters the intervertebral foramen 
with the spinal nerve where it gives off a ven- 
tral (anterior) and a dorsal (posterior) radic- 
ular artery which penetrates the dura meter. 
While there is a radicular artery for each spinal 
nerve root, many of the radicular arteries are 
Left 
coro- 
nary a. 
u-i I / r anterior 
Valvules of 
pulmonory 
valve 
Anterior 
interventriculo 
- circumflex 
Rt. coronary a. 
, — Right — I 
Cusps of p anterior 
mitral 4 
valve posterior - 
Cut edge of - 
left atrium 
Cut edge of 
right atrium 
Figure 21. — Diagram of the valves of the heart, in a 
view from above, with both atria cut away and the 
aorta and the pulmonary trunk cut a little above the 
levels of their valves. 
Reproduced by permission from: W. Henry Hollinshead, TEXT- 
BOOK OF ANATOMY (ed. 2). Copyright (1967). Hoeber Medical 
Division — Harper & Row., New York. 
small and exhaust themselves in the nerve roots. 
The radicular arteries, of which there are us- 
ually six to eight pairs larger than 300 microns, 
are important sources of collateral circulation to 
the ventral spinal arteries. They are: one pair 
in the upper cervical area; one to two pairs in 
the lower cervical area ; one to two pairs in the 
upper thoracic area; none to one pair in the 
middle thoracic area ; and one pair in the lower 
thoracic region. 
In the lumbar region the intervertebral 
branches of the lumbar and sacral arteries 
furnish radicular branches to the anterior 
spinal artery. 
THE ANATOMY OF THE VERTEBRAL-BASILAR 
SYSTEM OF DOG IN RELATION TO MAN AND 
OTHER MAMMALS 
According to Rittman and Smith ^ more than 
two-thirds of the arterial blood reaches the dog 
brain by way of the vertebral-basilar system, 
yet the relatively few accounts of the anatomy 
of this system in the dog mention only its most 
striking features.'^-'' 
The major arterial system to the brain in 30 
dogs v^as studied following perfusion of the 
arterial system with neoprene latex and with 
