The Sphenoid Bone: A Butterfly-Shaped Wonder of the Skull
By Caroline Barrow CST-D MCSS, BSc
There are many intricacies to the bones of the skull. I wonder if you have a favourite?
Many people favour the sphenoid for its delicacy and butterfly-like beauty, alongside the maxilla and temporal bones. Its greater and lesser wings flare out from a central body and the delicate pterygoid processes point downwards, as anchors for the palatines of the back of the hard palate. See what you think…
Why the Sphenoid Matters in CranioSacral Therapy
It’s the King Pin!
Many people working with CranioSacral Therapy love the sphenoid because it acts as a linchpin within the cranium. It articulates with all the cranial bones, including the frontal, temporal, parietal, occiput and ethmoid bones. It also connects with the vomer, palatines and maxilla behind the hard palate, as well as the zygoma in the lateral part of the orbit.
Cranial osteopath Dr Sutherland first described the variety of ‘lesions’ the sphenoid can develop. He explored the subtle ways the bone can twist, affect neighbouring bones and be influenced by them in return.
As we will see shortly there is so much going on in, around and through this bone that working with it can have quite an effect.
Anatomy of the Sphenoid: Inside the Cranium
You can look at it from inside and out
The easiest place to start looking at it is from inside the cranium. You see the curves of the greater wings as they make up part of the middle fossa of the cranial floor and the body in the midline with its rectangular bumpy surface for articulation with the occiput at the sphenobasilar junction. This is a synchondrosis, or a fibrous joint that ossifies by the mid 20s or so; it is also a joint that causes some to question how the sphenoid can have any even slight movement from the osteopathic/craniosacral standpoint, but that is a topic for another day!
Most of the lateral side of the greater wing articulates with the squamous part of the temporal bone, the very top part reaching up to the parietal, while the more posterior edge aligns with the petrous part of the temporals. Anterior midline (at the front, in the middle!) is the articulation with the delicate ethmoid, which extends inferiorally a cm or two, (‘into the page’ in the image above) as these bones make up the roof of the nasal cavity.
The Lesser Wing: A Delicate Feature
One delicate feature of this bone is the lesser wing.
This is a very thin piece that reaches out sideways from either side of the body, making up the very back part of the anterior cranial fossa (front top shelf in which the brain sits) articulating with the frontal bone as it does so. Many models make it appear as though the lesser wing joins the greater wing at its outer edge, but in reality the frontal bone creates the connection between them. There is a large hole between the greater and lesser wings which I will consider in Part 2.
The inward curving ends of the lesser wing attach the tentorium cerebelli, one of the big sheets of the dural membrane which slides in between the underside of the temporal lobe of the cerebrum and on top of the cerebellum, as do two upward pointing pieces at the back section of the body. These structures are called the anterior and posterior clinoid processes.
The Body of the Sphenoid and the Pituitary Fossa
The central area, known as the body of the sphenoid, contains a number of important anatomical features. Inside the bone itself are two holes, separated by a septum: the sphenoidal sinuses. Like the other sinuses in this region, the sphenoidal sinuses are lined with mucous membranes. The maxillary sinuses were covered previously, and similar structures are also found within the frontal bone and ethmoid. A tiny opening allows the sphenoidal sinuses to drain into the upper nasal cavity.
At the centre of the sphenoid body sits a dip, or fossa, called the sella turcica, also known as the pituitary fossa. This is where the pituitary gland rests. At the back of this area, a small rectangular section of bone called the dorsum sellae rises upwards, forming the point from which the posterior clinoid processes extend.
Pterygoid Processes and TMJ Connection
Looking from the outside….
Looking at the underside of the skull, you can see the two pterygoid (‘ter-a-goid’) processes extending downwards. Each process divides into a medial and lateral pterygoid plate. These provide attachment points for the medial and lateral pterygoid muscles of the TMJ. This creates another strong connection between the sphenoid and the mandible through muscular attachments.
The pterygoid plates also connect with the palatine bones in a more complex arrangement. For now, it is enough to note their position. These are some of the main features of the sphenoid bone. In Part 2, we’ll explore the many openings within and around the sphenoid, and what passes through them.
Caroline Barrow
The College of Body Science began in 2001 with a focus on teaching anatomy and physiology to complementary therapists. More than two decades later, the fascination with these intricate details of the body is still as strong as ever. Hopefully you’ll find them just as exciting too!
You can check out the online courses we offer at www.collegeofbodyscience.com. Check me out with the free ones and if you like my vibe there are some longer programmes to enjoy too!
