General Topography and Cervical Part
The initial segment of the internal carotid artery is located deeper and more medially than the external carotid artery, although at its very origin it lies posterior and lateral to it. In the neck, the vessel is constantly accompanied by the internal jugular vein (v. jugularis interna), which lies lateral to it.
The first segment is the cervical part (pars cervicalis). The artery ascends along the lateral wall of the pharynx, passing medially to the parotid gland. It is physically separated from the glandular tissue by the styloglossus and stylopharyngeus muscles. The main anatomical feature of this segment is that the artery gives off no branches here. At the very beginning of the cervical part (at the level of the bifurcation) lies the carotid sinus (sinus caroticus), a small fusiform dilation of the wall containing baroreceptors that monitor blood pressure. The cervical part terminates where the vessel enters the carotid canal of the petrous part of the temporal bone.
Petrous and Cavernous Parts
Inside the skull, the topography of the vessel becomes more complex as it passes through two specific segments:
- Petrous part (pars petrosa). The vessel runs inside the carotid canal of the temporal bone, exactly mimicking its natural S-shaped bends. The artery emerges from the canal into the cranial cavity through the foramen lacerum (foramen lacerum) and enters the carotid sulcus on the body of the sphenoid bone. In this segment, small caroticotympanic arteries (aa. caroticotympanicae) branch off to the mucosa of the tympanic cavity, along with the artery of the pterygoid canal (a. canalis pterygoidei), which supplies the pterygopalatine ganglion.
- Cavernous part (pars cavernosa). The artery penetrates directly into the cavernous venous sinus (sinus cavernosus), becoming literally surrounded by venous blood. Important cranial nerves pass close to it: the oculomotor (III), trochlear (IV), and abducens (VI) nerves, as well as the ophthalmic and maxillary nerves (V₁ and V₂). Here, the vessel makes an anterior and superior bend, giving off branches to the walls of the sinus, the tentorium cerebelli, the meninges, the nerves, and the inferior hypophysial artery (a. hypophysialis inferior) to the posterior lobe of the pituitary gland.
Cerebral Part and Ophthalmic Artery
The cerebral part (pars cerebralis) begins near the lesser wings of the sphenoid bone. Here, small vessels branch off: the branch of the clivus (r. clivi) to the dura mater and the superior hypophysial artery (a. hypophysialis superior) to the anterior lobe of the pituitary gland.
The largest branch of the cerebral segment is the paired ophthalmic artery (a. ophthalmica). It enters the orbit via the optic canal (canalis opticus) alongside the optic nerve, lying lateral to it. This vessel features an extensive network of branches:
- Lacrimal artery (a. lacrimalis) — to the lacrimal gland and eyelids;
- Central retinal artery (a. centralis retinae) — penetrates into the optic nerve;
- Ciliary arteries (posterior and anterior) — to the choroid, ciliary body, and conjunctiva;
- Muscular branches — supplying the extraocular rectus and oblique muscles;
- Ethmoidal arteries (anterior and posterior) — supply the ethmoidal air cells and nasal cavity;
- Supraorbital artery (a. supraorbitalis) — emerges onto the frontal region.
At the medial angle of the eye, the ophthalmic artery divides into the supratrochlear artery and the dorsal nasal artery (a. dorsalis nasi). The latter forms a critically important clinical anastomosis with the angular artery (which belongs to the external carotid artery system).