. 
MORPHOLOGY OF THE ARTERIES. 
889 
body, the kidney, and the ovary or testicle, and it is accordingly termed the intermediate visceral 
artery. The third artery, which is known as the splanchnic segmental artery, springs from 
Fic. 607.—DIAGRAM OF THE CEPHALIC AORTIC ARCHES, AND OF THE SEGMENTAL AND INTERSEGMENTAL 
ARTERIES IN THE REGION IN FRONT OF THE UMBILICUS. 
C.A.A TI, II, I1I, 1V, V. The cephalic aortic arches. 
Co. Anastomosing vessel between the primitive 
ventral aorta and the ventral somatic 
anastomosis. 
D.D. Dorsal division of a somatic segmental artery. 
D.Sp. Dorsal splanchnic anastomosis. 
L.B. Lateral branch of ventral division of somatic 
segmental artery. 
L.E.D. Branch to lateral enteric diverticulum. 
P.D.A. Primitive dorsal aorta. ; 
Po.C.  Post-costal anastomosis. 
the ventral surface of the descending aorta. 
Po.T. Post-transverse anastomosis. 
Pr.C. —- Pre-costal anastomosis. 
P.V.A. Primitive ventral aorta. 
So.S.A1, 2, 3, 4, 5, 6, 7, 8. Somatic segmental 
arteries. 
Sp.S.A. Splanchnic segmental arteries. 
V.D. ‘Ventral division of a somatic segmental artery. 
V.E.D. Branch to ventral enteric diverticulum. 
VEN Vitelline vessels. 
V.So. Ventral somatic anastomosis. 
V.Sp. Ventral splanchnic anastomosis. 
It runs in the tissues developed from the splanchnic 
mesoderm, and supplies the wall of the alimentary canal. 
The somatic segmental arteries form in the early embryo a regular series of paired vessels 
throughout the cervical, dorsal, lumbar, and sacral regions. 
lumbar regions that their original 
characters are retained. The paired 
vessels pass backwards by the sides 
of the vertebree, and divide into 
dorsal and ventral branches which 
accompany the corresponding 
anterior and posterior primary 
divisions of the spinal nerves. 
The ventral branches run out- 
wards between the ribs in the 
dorsal region, and im corresponding 
positions in the lumbar region. 
They are connected together, near 
their commencements, by a series 
of precostal anastomoses which pass 
in front of the necks of the ribs, 
and they are also connected together 
near their terminations by ventral 
anastomosing channels which run 
WAVE 
Fic. 608.—DIAGRAM OF THE CAUDAL AORTIC ARCH, AND OF THE 
SEGMENTAL AND INTERSEGMENTAL 
BEHIND THE UMBILICUS. 
It is, however, only in the dorsal and 
ARTERIES IN THE REGION 
in the thoracic region behind the Cd.A.A. Caudal aortic arch. So.S.A. Somatic segmental 
costal cartilages, and in the lumbar D.Sp. Dorsal splanchnic ana- _ arteries. 
region behind or in the substance stomosis. Sp.s.A. Splanchnic segmental 
of the rectus abdominis muscle. nae ee ae eta V.ED(H nee Anica 
: ; : a aC. arietal branch from .E.D.(Hy). Bra a ventre 
pigs smears ane De =e thaahe caudal arch. enteric diverticulum. 
ifs Be ] t 4 1 t i i Mee P.D.A. | Primitive dorsal aorta. Vi.c. Visceral branch from the 
USES sateral CULANeOUS, DlancwmOt PVids, Primitive ventral aorta: caudal arch. 
a spinal nerve. 
The dorsal branches run back- 
V.V. Vitelline vessels. 
wards between the transverse processes of the vertebra ; they are connected behind the necks of 
the ribs by post-costal anastomoses, and again behind the transverse processes of the vertebre by 
