a) Squamous – curved blade that extends posterior to the occipital foramen.

b) Basilar – anterior to the occipital foramen and thick.

scaly:

External face : posterior and convex. It has the following structures:

• External Occipital Protuberance – located between the apex of the bone and the foramen magnum
• External Occipital Crest
• Supreme Occipital (Nucal) Line – site of insertion of the galea aponeurotic. The external occipital protuberance is located laterally
• Superior Occipital (Nuchal) Line – located below the superior nuchal line
• Inferior Occipital (Nuchal) Line – just below the superior nuchal line

Inner Face : located anteriorly. It has the following structures:

• Cruciform Eminence – divides the inner face into four fossae
• Internal Occipital Protuberance – point of intersection of the four divisions
• Sagittal sulcus – houses the posterior portion of the superior sagittal sinus
• Internal Occipital Crest – inferior portion of the cruciform eminence
• Transverse Sinus Groove – lateral to the internal occipital bulge
• Superior Occipital Fossa (Brain)
• Inferior Occipital Fossa (Cerebellar)

Basic :

• foramen magnum – large oval opening that gives passage to the medulla oblongata (brain stem – medulla) and its membranes (meninges), cerebrospinal fluid, nerves, arteries, veins and ligaments.

Side :

• Occipital Condyles – are oval in shape and articulate with the 1st cervical vertebra (Atlas)
• Hypoglossal Canal – small excavation at the base of the occipital condyle that gives exit to the hypoglossal nerve (12th cranial nerve) and entry to a meningeal branch of the ascending pharyngeal artery.
• Condylar canal – next to the foramen magnum (gives the way to veins)
• Jugular Process – located lateral to the occipital condyle

The Occipital articulates with six bones: Parietal (2), Temporal (2), Sphenoid and Atlas.

OCCIPITAL - EXTERNAL VIEW

Source: SOBOTTA, Johannes. Atlas of Human Anatomy. 21 ed. Rio de Janeiro: Guanabara Koogan, 2000.