Inferior View Of The Skull

Inferior View Of The Skull:

In this section we’ll look the skull inferiorly. The bones that form this part of the skull are the Maxilla, Palatine, Sphenoid, Occipital and Temporal Bone. Inferiorly, the skull is divided into 3 parts: 

1. An anterior part –that includes the teeth and the hard palate
2. A middle part –that extends from the base of the hard palate to the anterior margin of the Foramen Magnum
3. A posterior part –that extends from the anterior margin of Foramen Magnum, all the way to the superior nuchal line posteriorly.

Now let’s examine the individual parts and the bones they house, in detail.

Anterior Part:

This part mainly forms the teeth and the hard palate.

The teeth are planted in the Alveolar Arch of the maxilla.

The Hard palate is formed anteriorly by the paired Palatine process of the maxilla and posteriorly by the Horizontal Plates of the Palatine Bone. The palatine process of the maxilla meets at the midline to form the intermaxillary suture, posteriorly with the palatine bone at the palatomaxillary suture. The paired horizontal plate of Palatine bone meets at the midline at the interpalatine suture. Together all the three sutures form the crucifix suture.

More of the bony feature include;

• The incisive fossa –present behind the incisors. 
• The Greater Palatine Foramen leading to Greater palatine canal –present on the posterolateral border of the hard palate. 
• The Lesser Palatine Foramen Leading to Lesser Palatine Canal –present behind the Greater palatine foramen, on the pyramidal process of palatine bone. 
• And the Posterior Nasal Spine –at the posterior free border of the hard palate

Middle Part:

For sake of description, the middle part if further divided into 2 parts: 

• Anterior Half –the sphenoid and vomer bones.
• Posterior Half –the occipital and paired temporal bones.

Anterior Half of the Middle part of the Base of the skull is formed by Vomer and Sphenoid Bone.

Vomer bone rests on the body of the sphenoid bone at the midline. It forms the bony nasal septum, separating the two Choanae.

Sphenoid bone is composed of 4 parts: 

1. The Body
2. The Pterygoid Processes.
3. The Lesser Wing
4. The Greater Wing

However only 3 parts (excluding the lesser wing) of the sphenoid bone are visible from the Inferior view of the skull. The Body of the Sphenoid Bone is place at the midline and comprises of 2 sphenoid sinuses divided by a septum. It articulates anteriorly with the Vomer, Ethmoid, Palatine bones, posteriorly with the base of occipital bone, and laterally with the temporal bone.

The two Pterygoid Processes project inferiorly from the junction of body and greater wing of the sphenoid bone. These processes comprise of the medial and lateral plate separated by the Pterygoid fossa. The bony features i.e the Pterygoid hamulus, pteregoid fossa and the scaphoid fossa are labeled on the models.

The Greater Wing of the Sphenoid bone not only forms the base of the skull but also contributes to the lateral wall as well. It articulates laterally and posteriorly with parts of the temporal bone.

Posterior Half of the middle part of the base of the skull is composed of occipital and temporal bones. The occipital bone or more specifically the basilar part of the occipital bone is bounded anteriorly by the body of the sphenoid bone, laterally by the temporal bone and posteriorly it is limited by the foramen magnum. Prominent feature on the basilar part of the occipital bone is the Pharyngeal Tubercle which provides attachment for part of the pharynx to the base of the skull. The occipital bone is discussed in detail later in the ‘posterior part’ of the middle part of the base of the skull.

Temporal bone is found immediately lateral to the sphenoid and basilar part of occipital bone. The petrous part of temporal bone is bounded anteriorly by the greater wing of sphenoid bone and posteriorly by the occipital bone. Lateral to the junction of the basilar part of occipital bone and body of sphenoid, is the irregular shaped foramen Lacerum. Posterolateral to the foramen Lacerum is the carotid canal for the internal carotid artery. Lateral to the greater wing of the sphenoid bone is the squamous part of the temporal bone that houses the Mandibular Fossa for the temporomandibular joint. Anterior to that is a prominent feature, the Articulate Tubercle.

Posterior Part:

Posterior part of the base of the skull extends from the anterior border of the foramen magnum all the way to the external occipital protuberance posteriorly. It consists of occipital bone medially and temporal bone laterally.

Occipital Bone is the major bony element in this part of the base of the skull. It comprise of 4 parts: 

• The squamous part -posterior to the foramen magnum
• The lateral parts –lateral to the foramen magnum
• The basilar part –anterior to the foramen magnum

The squamous and lateral parts form the posterior part of the base of the skull.

The most prominent feature of the squamous part of the occipital bone is the Occipital Crest, extending from the external occipital protuberance to foramen magnum posteriorly. On each anterolateral border of the foramen magnum are occipital condyles for the articulation of the skull with the first (C-1 atlas) Vertebra. Posterior to each condyle is a depression –the condylar fossa- containing a condylar canal. Anterior and superior to each condyle is the large hypoglossal canal. Lateral to that is the large jugular foramen, formed by the jugular notch of occipital and petrous part of temporal bone.

Temporal Bone is found lateral to the posterior part of the base of the skull. The parts of temporal boon seen here are the mastoid process (and mastoid notch) and the styloid process. Both of which provide attachment for muscles. Between the two is Stylomastoid Foramen for the facial nerve.