Page 236 - My FlipBook

246 ANATOMY. ;
side at the posterior inferior extremity of the pons varolii to form the
basihir artery.
TAf Branches of the Vertebral Artery are divided into cervical and
encranial. The cervical branches are the lateral spinal and muscular
the encranial branches are the posterior meningeal, posterior spinal,
anterior spinal, and the posterior cerebellar. The distribution of these
branches is generally implied in their names.
The Basilar Artery is formed by the union of the right and left ver-
tebral arteries, which takes place at the posterior inferior extremity of
the pons varolii. From this point it passes forward and upward within
a groove along the middle of the superior surface of the basilar process
of the occipital bone to the anterior extremity of the pons, close to the
posterior clinoid processes. Here it divides into the posterior cerebral
arteries already described.
The Branches of the Basilar Artery are the trans v'erse, six or eight in
number, which supply the under surface of the pons ; the right and left
auditory, whicli pass through the internal auditory meatus of the tempo-
ral bone, together with the auditory nerve, and supply the labyrinths of
the ear ; the anterior or inferior cerebellar, right and left, which supply
the anterior inferior portion of the cerebellum and other structures in
juxtaposition, and anastomose with the inferior cerebellar branches of
the vertebral; the superior cerebellar, right and left, which supply
through their numerous branches the cerebellum and other structures
in the vicinity; and the terminal or posterior cerebral arteries previously
described.
The Thyroid Axis is about 6 mm. (| inch) in calibre and but a few
lines in length. It arises from the anterior superior surface of the first
part of the subclavian artery, and passes upward a very short distance
close to the proximal border of the anterior scalenus muscle. Here it
breaks up into three branches, inferior thyroid, suprascapular, and trans-
versal is colli.
The Inferior Thyroid Artery is about 31 mm. (^ inch) in calibre. It
arises from the tliyroid axis, and could be reo;arded as a continuation
of this artery. From its origin it passes directly upward in front
of the vertebral artery and under the central portion of the omo-hyoid
muscle. Sliglitly above tlie muscle, opposite the fifth cervical vertebra,
it curves inward in a tortuous manner, and passes beneath the slieath of
the large vessels of the neck and sympathetic nerve to the inferior part
of the thyroid body. Here it breaks up into fine branches which sup-
ply tlie gland and anastomose with brandies of the superior thyroid
artery, as >vell as the corresjionding artery of the opj^osite side. The
other branches of the inferior thyroid are the ascending cervical, inferior
laryngeal, and tracheal.
The Ascending Ccrrical Artery is ;ibout 2 mm. (y^^- inch) in calibre,
and arises from the inferior thyroid just as it curves inward behind the
sheath of the large vessels of the neck. It jmsses upward immediately
anterior to the pln-enic nerve in the interspace between the anterior sca-
lenus and tlie rectus capitis anticus major muscles, and is distributed
through small branches to these muscles, a few branches extending
across the neck to anastomose with offshoots from the vertebral. Other