This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Occipital Artery arises from the posterior part of the external carotid, nearly opposite to the origin of the lingual artery: it may be divided into three stages.
In its first stage it lies in the anterior superior lateral triangle of the neck, running towards the digastric groove of the temporal bone, and extends as far as the anterior margin of the sterno-mastoid muscle, passing obliquely over the concavity of the arch formed in the neck by the hypo-glossal nerve, which is therefore said to pass round it. In this stage the occipital artery at first runs along the inferior margin of the posterior belly of the digastric muscle; more posteriorly, however, this muscle partly covers the artery, and forms one of its superficial relations; still more superficially we find a portion of the parotid gland, the fascia of the neck, a few fibres of the platysma, and the integuments. Its deep-seated relations are the internal carotid artery, the pneumogastric nerve, and the internal jugular vein, from which last it is separated by the spinal accessory nerve.
In its second stage it passes somewhat horizontally from before backwards, and in its course is covered by the following parts :—the skin and a strong layer of condensed areolar tissue, the sterno-mastoid muscle, and behind this by the splenius capitis; then deeper, by the trachelomastoideus or complexus minor, then by the mastoid process itself, and still deeper by the origin of the posterior belly of the digastric muscle. In this stage the artery is lodged in a distinct, but frequently superficial, groove in the temporal bone, internal to the deep groove for the posterior belly of the digastric, and lies on, or more correctly speaking, external to the outer margin of the rectus capitis lateralis muscle, and above the transverse process of the atlas; it then passes across the insertion of the obliquus superior, and afterwards arches over the insertion of the complexus major muscle: it occasionally lies underneath this muscle.
In its third stage it arrives at the posterior region of the neck by passing through a condensed fascia, which unites the posterior margin of the sterno-mastoid muscle , with the anterior border of the trapezius at their insertions, and then ascends obliquely inwards and ramifies on the occipital region of the head. In this stage it appears in the triangular space which the splenii capitis muscles form by their divergence on the middle line in the superior part of the back of the neck, and then ascends on the back of the head, through the fibres of the occipital muscle, in company with the posterior branch of the second cervical nerve.
The occipital artery gives off the following branches:
Muscular. Descending Cervical.
Posterior Meningeal. Mastoidean.
The Muscular Branches are distributed to the posterior belly of the digastric muscle, and to the stylo-hyoid and sterno-mastoid muscles. It occasionally gives off the stylo-mastoid artery, which enters the stylo-mastoid foramen and anastomoses with a branch of the middle meningeal from the internal maxillary.
The Posterior Meningeal branch arises from the occipital as it lies on the side of the internal jugular vein; it enters the foramen lacerum posterius, and is distributed to the dura mater in the posterior and lateral regions of the interior of the cranium.
The Descending Cervical branch arises from the artery as it lies under cover of the splenius, near its posterior margin: it sends branches to the muscles in the immediate neighborhood, and anastomoses with the cervicalis superficialis and cervicalis profunda arteries. There are sometimes two or even three descending cervical branches present.
The Mastoidean Branch, at its origin, corresponds to the posterior surface of the mastoid process of the temporal bone; it passes through the mastoidean foramen in this part of the bone, accompanied by a vein, sends minute branches to the mastoid cells, and is distributed within the cranium to the dura mater of the occipital fossae. As the occipital artery is arching over the ob-liquus superior muscle, it communicates with the vertebral artery; sometimes it gives off the stylo-mastoid artery.
The Terminating Branches of the occipital artery ascend tortuously in the course of the lambdoidal suture to supply the occipito-frontalis muscle and integuments, and to anastomose with the temporal and posterior auricular arteries, and with the occipital of the opposite side. We sometimes find one of those small branches passing through the parietal foramen to be lost in the dura mater.
Should it ever be necessary to tie the occipital artery in case of profuse hemorrhage from any of its branches, the incision already recommended for exposing the external carotid will also expose this vessel in the commencement of its first stage; or an incision may be made along the lower margin of the posterior belly of the digastric muscle, on raising which the artery is brought into view. Care should be taken not to injure or include the hypo-glossal nerve.
The depth of this artery behind the mastoid process is very variable, and unless there be a wound to guide us to the vessel, it is not an operations that should be attempted.