Part 66

=The Common Carotid.=—Near the last cervical vertebra the two carotid arteries occupy the same channel, to which they are attached by fascia, and, lying close to the inferior surface of the bodies of the cervical vertebræ, are covered by the colli muscles. Near the third or the fourth cervical vertebra, the two carotid arteries separate. Near the atlas each carotid divides into the carotis cerebralis and carotis externa. Near this division the superior cervical artery branches off. This latter artery extends down the neck in company with the pneumogastric nerve and the jugular vein, supplies the skin and the neck muscles, and anastomoses with the inferior cervical artery and the subcutaneous colli artery.

The occipital artery originates either from the carotis communis or sometimes from the superior cervical.

BRANCHES OF THE CAROTIS CEREBRALIS

The branches of the carotis cerebralis are as follows:

1. The =occipitalis= (Fig. 72, No. 18), which in turn gives off, first, the occipitalis sublimis. The occipitalis sublimis supplies the outer and the middle portion of the digastricus and the posterior mylo-hyoideus muscle. It also gives off, second, the occipitalis profunda which supplies the inner portion of the digastricus muscle and becomes the meningeal artery, which passes through the foramen vagi, entering the brain cavity, where it supplies the coverings of the brain as far as the sella turcica. Superficial branches of this artery are distributed to the muscles in the region of the atlas and anastomose with the vertebral artery.

2. The =ophthalmica externa=, which passes below the articulation of the quadrate bone, around the tympanic cavity, enters the canalis caroticus, and passes into the cranial cavity. The ramus occipitalis, passing out of the same foramen, again enters the diploë of the cranium; then after passing dorsally over the upper outer semicircular canal of the ear, passes backward through the occipital bone.

The ophthalmica externa (Fig. 72, No. 9) forms a main trunk and gives off two branches: the temporal artery and the recurrent ophthalmic. The recurrent ophthalmic gives off the rete temporalis, rete ethmoidalis, a branch to the orbital gland, and finally anastomoses with its own branches and with those of the internal ophthalmic at the olfactory foramen and aids in forming the ethmoidal artery. These arteries supply blood by giving off branches to the muscles of the eye, sclerotic coat, iris, choroid coat, and the ciliary bodies. It gives off another branch to Harder’s gland, and finally anastomoses with the ethmoidalis.

3. The =plexus temporalis=, rete mirabile ophthalmicum, or wonderful network (Fig. 72, No. 8), is formed between the second and the third trunk of the trigeminus nerve and the rete ophthalmicum.

Inferior to this is the alveolar plexus, which plexus accompanies the third branch of the trigeminus into the lower jaw. Two main branches form this plexus, one coming from the carotis facialis, which anastomoses with the alveolar artery.

The palpebral plexus lies between the trunks of the trigeminus, and supplies mainly the lower eyelid.

The plexus muscularis extends to the fifth portion of the temporal muscle.

The plexus lacrimalis forms on the posterior orbital wall on the ramus ethmoidalis and supplies the lacrimal gland and the upper eyelid. It anastomoses with branches from the facial artery.

The ramus ciliaris posticus supplies the inferior rectus and the external rectus muscle of the eyeball. It anastomoses with the ophthalmica externa.

The median meningeal artery passes through the foramen occupied by the second branch of the trigeminal nerve. Passing into the cranial cavity, it supplies the dura mater. Before passing into this foramen, small branches are given off, which supply the skin and the temporal muscle; and some branches anastomose with the superior cervical and the ethmoidal arteries.

=4. The Cerebral Artery.=—Each cerebral artery enters the cranial cavity through the canalis caroticus located in the sphenoid bone, passes forward medially from the cochlea, dorsally from the Eustachian tube, and passes through a small canal which opens on the inner surface of the sella turcica. Originating in this foramen, the sphenoid artery divides into two branches which anastomose with the pterygoidean and the pterygo-pharyngeal artery and which supply the upper jaw and the throat regions.

The spheno-maxillaris artery supplies the gums.

The right and the left cerebral arteries unite at the sella turcica. After this union they divide again immediately and pass to the base of the brain, where they give off twigs to the optic nerve, to the optic chiasm, and where also is given off the arteria retinæ centralis. Passing posteriorly each cerebral artery gives off the ramus posterior, and then passes to the side of the cerebellum.

The basilar artery, a continuation of the anterior spinal artery, is located ventrally and mesially to the cerebellum. Laterally and inferiorly the basilar artery gives off the inferior cerebellar artery.

The ramus anterior is given off from the cerebralis artery and continues as the internal ophthalmic artery. The ramus anterior also gives off the sylvian artery, which supplies the sides of the cerebrum and the middle brain. In the fissure between the hemispheres and the optic thalamus is located the arteria cerebri profunda. This artery passes along the median surface of the cerebrum and in its course supplies the adjacent parts. It enters into the formation of the choroid plexus of the lateral ventricle.

The internal ophthalmic artery extends out of the cranial cavity, through the optic foramen, into the orbital cavity. It passes upward along the interorbital wall and supplies the optic nerve, the trigeminus nerve trunk, and the eye muscles, and dorsally anastomoses near the olfactory nerve with the rete ethmoidale and the external ophthalmic artery, and continues as the ethmoidal artery.

The ethmoidal artery supplies the supra-orbital gland and the gland of Harder. It gives off twigs to the rete ophthalmicum and other branches to the skin of the frontal region, where it anastomoses with branches of the external facial artery. These branches in the frontal region are rather large. Large branches are given off to the comb.

The arteria ethmoidalis externa originates in the nasal cavity from a division of the ethmoidal artery.

The external ethmoidal artery passes below the lacrimal bone, extends forward, supplies the walls of the nasal cavity, and finally sends a branch anteriorly into the upper median portion of the jaw bone, and other branches to the septum nasi and other parts of the nasal cavity.

There are frequent anastomoses between the ethmoidalis interna, the facialis, and the spheno-maxillary artery.

The internal ethmoidal artery supplies principally the posterior turbinated bones and septum nasi.

BRANCHES OF THE EXTERNAL CAROTID ARTERY

Branches from the external carotid and the facial artery supply the tongue and its muscles, the larynx, the lower jaw bone, the gums, and the upper lateral facial region.

The external carotid (Fig. 62, No. A, 8) gives off the following branches: