THE SPHENOID BONE. 135 



the basilar groove of the occipital bone, supporting the pons and the basilar 

 artery. Anteriorly and laterally the angles of this ridge project over the fossa 

 hypophyseos in the form of prominent tubercles, called the processus clinoidei 

 posteriores (posterior clinoid processes). To these are attached the tentorium 

 cerebelli and interclinoid ligaments. In front of the fossa hypophyseos there is a 

 transverse elevation, the tuberculum sellse, towards the lateral extremities of which, 

 and somewhat behind, there are oftentimes little spurs of bone, the processus 

 clinoidei medii (middle clinoid processes). In front of the tuberculum sellse is the 

 sulcus chiasmatis, which passes laterally on either side to become continuous, 

 between the roots of the small wings, with the optic foramina. 



This groove is liable to considerable variations, and apparently does not always serve for the 

 lodgment of the optic chiasma. (Lawrence, " Proc. Soc. Anat.," Journ. Anat and Physiol. 

 vol. xxviii. p. 18.) 



In front of the sulcus chiasmatis, from which it is often separated by a thin sharp 

 edge, the superior surface continues forwards on the same plane as the upper surfaces 

 of the small wings, and terminates anteriorly in a ragged edge, which articulates with 

 the lamina cribrosa of the ethmoid, and has often projecting from it, in the median 

 plane, a pointed process, the sphenoidal spine. The lateral aspects of the body are fused 

 with the great wings, and in part also with the roots of the pterygoid processes. 

 Curving along the side of the body, above its attachment to the great wing, 

 is an f- shaped groove, the sulcus caroticus (carotid groove), which marks the 

 position and course of the internal carotid artery. Posteriorly, the hinder margin 

 of this groove, formed by the salient lateral edge of the posterior surface of the 

 body, articulates with the apex of the petrous portion of the temporal bone, and 

 is hence called the petrosal process ; just above this, on the lateral border of the 

 dorsum sellae, there is often a groove for the abducent nerve. 



The anterior surface of the body displays a vertical, median crista sphenoidalis 

 (sphenoidal crest), continuous above with the . sphenoidal spine, and below with 

 the pointed projection called the sphenoidal rostrum. This crest articulates in front 

 with the perpendicular plate of the ethmoid. On each side of the median plane 

 are seen the irregular openings leading into the sphenoidal air sinuses, the thin 

 anterior walls of which are in part formed by the absorption of the sphenoidal 

 conchse (O.T. turbinated bones) with which in early life they are in contact. With 

 exception of a broad groove leading downwards from the apertures above mentioned, 

 which enters into the formation of the roof of the nasal cavity of the corre- 

 sponding side, the lateral aspects of this surface of the bone are elsewhere in 

 articulation with the labyrinths of the ethmoid and the orbital processes of the 

 palate bones. The sphenoidal rostrum is continued backwards for some distance 

 along the inferior surface of the body, where it forms a prominent keel which 

 fits into the recess formed by the alee of the vomer. The edges of the alae 

 serve to separate the rostrum from the incurved vaginal processes at the roots of 

 the medial plates of the pterygoid processes. Posteriorly, the inferior surface of the 

 body of the sphenoid is rougher, and covered by the mucous membrane of the roof 

 of the pharynx ; here, occasionally, a median depression may be seen which marks 

 the position of the inferior extremity of a foetal channel, called the canalis 

 craniopharyngeus. 



Alae Parvae. The small wings are two flattened triangular plates of bone 

 which project forwards and laterally from the anterior and upper part of the body 

 of the bone, with which they are united by two roots which enclose between 

 them the optic foramina for the transmission of the optic nerves and ophthalmic 

 arteries. Of these roots, the posterior springs from the body just wide of the 

 tuberculum sellae, separating the carotid groove behind from the optic foramen 

 in front ; laterally this root is confluent with the recurved posterior angle of the 

 small wing, forming the projection known as the processus clinoideus anterior 

 (anterior clinoid process), which overhangs the anterior part of the body of the 

 bone and affords an attachment to the tentorium cerebelli and interclinoid liga- 

 ments. The anterior root, broad and compressed, unites the upper surface of the 

 small wing with the anterior and upper part of the body. Laterally, the lateral 



