40 SPHENOIDAL BONE. 



carotid foramen in the posterior border, is an irregular excavation 

 forming part of the jugular fossa, and divided into two parts by a 

 ridge and a sharp spine, the jugular process. Upon this ridge, at 

 the posterior margin of the carotid foramen, is a small opening 

 leading into the canal which transmits the tympanic branch of the 

 glosso-pharyngeal nerve (Jacobson's nerve). 



Borders. The superior border is sharp, and gives attachment to 

 the tentorium cerebelli. It is grooved for the superior petrosal 

 sinus, and near its extremity is marked by a smooth notch upon 

 which reclines the fifth nerve. 



The anterior border is grooved for the. Eustachian tube, and 

 forms the posterior boundary of the foramen lacerum basis cranii ; 

 by its sharp extremity it gives attachment to the tensor tympani 

 and levator palati muscles. The posterior border is grooved for the 

 inferior petrosal sinus, and excavated for the jugular fossa ; it forms 

 the anterior boundary of the foramen lacerum posterius. 



Developement. By five centres ; one for the squamous portion, 

 one for the mastoid, one for the petrous portion, one for the audi- 

 tory process, and one for the styloid process. 



Articulations. With Jive bones ; occipital, parietal, sphenoid, in- 

 ferior maxillary, and malar. 



Attachment of Muscles. To fourteen ; by the squamous portion, 

 to the temporal ; by the zygoma, to the masseter ; by the mastoid 

 portion, to the occipito-frontalis, splenius capitis, sterno-mastoid, 

 trachelo-mastoid, digasticus and retrahens aurem; by the styloid 

 process, to the stylo-pharyngeus, stylo-hyoideus, stylo-glossus, and 

 two ligaments the stylo-hyoid and stylo-maxillary; and by the 

 petrous portion, to the levator palati, tensor tympani, and stapedius. 

 SPHENOIDAL BONE. The sphenoid (tf^v, a wedge) is an irregular 

 bone situated at the base of the skull, wedged between the other 

 bones of the cranium, and entering into the formation both of the 

 cranium and face. It bears some resemblance in form to a bat 

 with its wings extended, and is divisible into body, wings, and pro- 

 cesses. 



The body forms the central mass of the bone, from which the 

 wings and processes are projected. From the upper and anterior 

 part of the body extend on each side two small triangular plates, 

 the lesser wings ; from either side and expanding laterally are the 

 greater wings ; proceeding backwards from the base of the greater 

 wings, the spinous processes ; and downwards, the pterygoid pro- 

 cesses. 



The body presents for examination a superior or cerebral sur- 

 face, an antero-inferior surface, and a posterior surface. 



Superior Surface. At the anterior extremity of this surface is a 

 small projecting plate, the ethmoidal spine, and spreading out on 

 either side the lesser wings. Behind the ethmoidal spine in the 

 middle line is a rounded elevation, the olivary process, which sup- 

 ports the commissure of the optic nerves. Passing outwards and 

 forwards from the olivary process, are the optic foramina, which 

 transmit the optic nerves and ophthalmic arteries. Behind the optic 



