Sphenoid bone

Two sphenoidal conchae are situated at the anterior and inferior part of the body.

Sphenoidal crest articulates with the perpendicular plate of ethmoid leading to formation of a part of the septum of nose.

These are asymmetrical air sinuses in the body of the sphenoid, closed by Sphenoidal conchae

This forms the floor of the middle cranial fossa. It presents (starting from the front):

These are two triangular wings projecting laterally from anterosuperior part of the body. Each consists of:

The greater part of the bone is ossified in cartilage. There are fourteen centers in all, six for the presphenoid and eight for the postsphenoid.

The sphenoidal conchae are each developed from a center that makes its appearance about the fifth month; at birth they consist of small triangular laminae, and it is not until the third year that they become hollowed out and coneshaped; about the fourth year they fuse with the labyrinths of the ethmoid bone, and between the ninth and twelfth years they unite with the sphenoid bone.

Soon after, the centers for the postsphenoid part of the body appear, one on either side of the sella turcica, and become blended together about the middle of fetal life.

Each medial pterygoid plate (except its hamulus) is ossified in membrane, and its center probably appears about the ninth or tenth week; the hamulus becomes chondrified during the third month, and almost at once ossifies (Fawcett).

About the fourth month, a center appears for each lingula and speedily joins the rest of the bone.

The presphenoid is united to the postsphenoid about the eighth month, and at birth the sphenoid is in three pieces [Fig. 4]: a central, consisting of the body and small wings, and two lateral, each comprising a great wing and pterygoid process.

In the first year after birth the great wings and body unite, and the small wings extend inward above the anterior part of the body, and, meeting with each other in the middle line, form an elevated smooth surface, termed the jugum sphenoidale.

By the twenty-fifth year the sphenoid and occipital are completely fused.

Between the pre- and postsphenoid there are occasionally seen the remains of a canal, the canalis cranio-pharyngeus, through which, in early fetal life, the hypophyseal diverticulum of the buccal ectoderm is transmitted.

The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not attain their full size until after puberty.

The sphenoid bone of humans is homologous with a number of bones that are often separate in other animals, and have a somewhat complex arrangement.

In the dog the sphenoid is represented by 8 bones: basisphenoid, alisphenoids, presphenoid, orbitosphenoids, pterygoids. These bones remain separate and are the:

This article incorporates text in the public domain from of the 20th edition of