(4.53)

Now we’ll move on to look at the sphenoid bone. The sphenoid bone is extremely complex! It extends all the way from one side of the skull to the other. The sphenoid bone forms important parts of the underside, and outside of the skull; and it forms part of the orbit. The sphenoid bone also forms this large and complicated part of the floor of the cranium.

Here’s a sphenoid bone all by itself. The sphenoid bone has a central part, and on each side three major projections - the lesser wing, the greater wing, and the pterygoid process. The central part of the sphenoid includes the clinoid processes, and the pituitary fossa. The central part of the sphenoid bone is hollow, as we’ll see.

The lesser wing, which is the highest part of the sphenoid bone, forms the sphenoid ridge, which separates the anterior and middle cranial fossae.

The underside of the lesser wing forms this small but important part of the back of the orbit. The greater wing of the sphenoid forms the front wall and part of the floor of the middle cranial fossa.

On the outside the greater wing forms this part of the temporal, and infratemporal fossae, and it also forms this large part of the lateral wall of the orbit .

The greater wing and the lesser wing are joined here, but more medially they’re separated by this triangular gap, the superior orbital fissure, which forms an large opening between the orbit, and the inside of the cranium.

Here’s the superior orbital fissure from the inside. We’ll get a better look at it in a minute. The pterygoid process of the sphenoid bone projects downward behind the maxilla.

The pterygoid process includes the lateral, and medial pterygoid plates, which are the attachments for some important muscles that we’ll see later. This hollow between the pterygoid plates is the pterygoid fossa. This little hook is the pterygoid hamulus. It’s a pulley, as we’ll see later.

The last bone on our list of large facial bones is another quite complicated bone, the ethmoid. The ethmoid bone is a little hard to understand at first, because in the intact skull most of it is hidden from view.

The only parts of the ethmoid bone that we can readily see are this small part of the floor of the anterior cranial fossa, the two cribriform plates with the crista galli in between, and this part in the medial wall of each orbit .

It’ll be easier to understand the ethmoid bone when we look at the nasal cavity in the next section. Till then we’ll leave the ethmoid bone alone. There are three smaller facial bones that we’ll look at briefly: the nasal, lacrimal, and palatine bones.

This is the nasal bone, this is the lacrimal bone. The two thin nasal bones form just the upper part of the bridge of the nose. The structural supports for the projecting parts of the nose are made of cartilage, as we’ll see later.

The little lacrimal bone forms the most medial part of the inferior orbital margin. This opening between the lacrimal bone and the ethmoid bone is for the nasolacimal duct, which takes tears from the corner of the eye to the nasal cavity.

Last of all we’ll look at the palatine bone. Here’s the lower part of it. On each side the palatine bone forms the posterior part of the hard palate, and part of the side wall of the nasal cavity. We’ll get a better look at the palatine bone when we look at the nasal cavity.