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1. Arterial System
The arterial system of Scoliodon consists of two types of
blood vessels-the afferent and efferent branchial arteries.
The atferent branchial arteries arise from the ventral
aorta and carry impure blood to the gills. The eferent
branchial arteries collect the purified blood from the gills
and carry it to the dorsal aorta.

3. Afferent branchial arteries :
The ventral aorta arises from the conus arteriosus and
runs forwards along the ventral surface of pharynx
right up to the posterior border of the hyoid arch,
where it bifurcates into two short branches, the
innominate arteries

4. Each innominate artery divides into first and second
branchial arteries. The first afferent branchial artery
runs along the hyoid arch and supplies branches to all
the gill lamellae of the hyoidean demibranch.
The second afferent branchial artery runs along the
posterior border of the first branchial arch and
supplies arterial branehes to the anterior and
posterior gill-lamellae of the first branchial arch

5. The third, fourth and fifth afferent branchial arteries arise
from the ventral aorta almost equidistant from one another
and run along the outer borders of the second, third and
fourth branchial arches, They supply the blood to the third,
fourth and fifth gill archeś respectively.

6. Eferent branch ial arteries : The blood from the
capillaries of gill-lamellae is collected by a series of
blood vessels called the eferent branchial
arteries.There are nine efferent branchial vessels on
each side. Of these the first eight join in pairs to form
four complete loops around the first four gill-clefts. The
ninth runs along the anterior border of the fifth gill-
cleft.

7. The four loops and ninth efferent branchial artery
are joined by short longitudinal connectives running
acroSs the interbranchial septa.Each of the four
efferent branchial loop is continued into an
epibranchial artery which runs backwards and
inwards to the mid-dorsal line. The four pairs of
epibranchial arteries unite to form the median
dorsal aorta. T'he half-loop of ninth efferent
branchial has no fenibranchial of its own.

8. Arteries of the head The first efferent branchial or
hyoidean efferent and a small part from the dorsal
aorta supply blood to the head. The first efferent
branchial vessel gives rise to three branches the
external carotid, afferent spiracular and hyoidean
epibranchial.

9. The external carotid artery arises from the ventral corner
-of the first efterent branchial vessel and runs along the
outer Surface of the hyoid arch. It divides into two
branches ; (1)The ventral mandibular supplying the
coraco-mandibular museles and muscles of lower jaw,
(2) superficial hyoid supplying the skin and sub-
cutaneous tissues over the ventral part of the hyoid arch.

10. The afferent spiracular artery arises at about the middle
of the hyoidean efierent. It runs forward on the outer side
of the hyomandibular and surrounds the spiracle by the
spiracular epibranchial artery across the floor of the orbit
and then enters the cramum through a small foramen

11. Just before entering the oranium 1t gives of the great
ophthalmic artery to the eye-ball. WItn oC Cranlum it
unites immediatelv with a branch of interna crod to
form the cerebral artery which is short vessel dividing
imediately into anterior and posterior cerebral
arteries

12. The hyoidean epibranchial artery arises from the dorsal
part of the first efferent and runs forward and inward
At the level of the orbit it receives a branch from the
dorsal aiota then divides into a stapedial and an
internal carotid.

13. stapedial artery runs forward and enters the orbit
where it gives two branches, one supplying the eye-
muscles and the superficial tissues in the region above
the auditory capsules and other supplying the anterior
boundary of the orbit. The former is called the inferior
orbital, while the latter is called the superior orbital,

14. The internal carotid passes inward along a groove in
the roof of the buccal cavity and enters the oranium
through a foramen. Within the cranial cavity it divides
into two branches one of which unites with its fellow of
the opposite side, while the other unites with the
epibranchialspiracular to form the anterior and
posterior cerebral arteries

15. Dorsal aorta and its branches
The dorsal aorta is formed by the union of four pairs of
epibranchial arteries. It runs back. wards along the whole
length of the body, lying beneath the vertebral column in
the trunk, In the tail region it continues within the haemal
canal of the tail vertebrae as the caudal artery.

16. Anteriorly it gives, off several small branches to the roof
of buccal cavity and the vertebral column, while two of
its branches run forward and outward to join the
hyoidean epibranchial of each side. Close to the union of
the fourth epibranchial arteries, the dorsal aorta gives
off a pair of small ves- sels, the subclavian arteries. Each
subclavian passes outwards and backwards to the
pectoral girdle and the pectoral fin

17. The coeliaco-mesenteric is a large median artery
arising from the dorsal aorte slightly behind the
junction of the fourth pair of epibranchial arteries. It
divides into two unequal branches: the smaller
coeliac and the larger anterior The coeliac artery
supplies the stomach and liver etc., and the anterior
mesenteric artery supplies the panereas, in- testine
and the rectum.

18. The lieno-gastric artery arises from the dorsal aorta a
short distance behind the origin of coeliaco-mesen-
teric. It is also a median blood vessel giving off
branches supplying the genital organs, stomach,
spleen and posterior part of the intes- tine. The
posterior mesenteric artery is a small median essel
which supplies the posterior end ot the gonads and
finally ends in the rectal gland.

19. The parietal arteries are a series of paired mesenteric.
vessels arising at intervals along the whole length of the
dorsal aorta and supplying the body wall. The renal
arteries are small paired Vesseis arising irom the parietal
arteries and supplying the kidneys. he iiac arteries are a
pair of arteries similar to the parietals, each of them
extending into the pelvic as a fenmoral artery and there
breaks up into capillaries.