EXTERIOR OF THE SKULL. 59 



The INFERIOR REGION, or external base of the skull, extending from the 

 incisor teeth to the occipital protuberance, and transversely from the 

 mastoid process and dental arch on one side to the corresponding points on 

 the other, is divisible, on removal of the lower jaw, into an anterior, 

 middle, and posterior part. 



The anterior part consists of the palate and the alveolar arch. It is 

 traversed longitudinally by a mesial suture, and transversely by that 

 between the maxillary and palate bones. Anteriorly, in the middle line, is 

 the anterior palatine foramen, with the four smaller foramina contained 

 within it; posteriorly, on each side, at the base of the alveolar border, is 

 the posterior palatine foramen, and externally and posteriorly to that, the 

 posterior and external small palatine foramina. The palate is surrounded 

 in front and on the sides by the alveolar arch and teeth of the upper jaw. 



The middle part, extending back to the front of the foramen magnum, is 

 the most complicated. Its central portion has been called the guttural fossa. 

 In the middle line is the basilar process of the occipital bone, and in front of 

 that the body of the sphenoid bone, concealed anteriorly by the extremity of 

 the vomer. On each side, the petrous portion of the temporal bone reaches 

 as far forwards as the extremity of the basilar process; and between the 

 petrous and squamous portions of the temporal is the back part of the great 

 wing of the sphenoid bone. Between this division of the base of the skull 

 and the palate are the posterior nares, separated by the vomer, and bounded 

 above by the body of the sphenoid bone, below by the horizontal plates of 

 the palate bones, and on the sides by the internal pterygoid processes. 

 Between the pterygoid plates is the pterygoid fossa; and placed in an 

 oblique line backwards and outwards from this are the foramen ovale, 

 foramen spinosum, and processus spinosus; while behind and parallel to 

 these is a groove for the Eustachian tube, formed by the margins of the 

 sphenoid bone and pars petrosa, leading into the Eustachian orifice, and in 

 a line with the fissure of Glaser. Between the apex of the pars petrosa, the 

 basilar process, and the sphenoid bone, is the foramen lacerum anterius basis 

 cranii, called also foramen lacerum medium, on the external wall of which 

 opens the carotid canal, and on the anterior the Vidian canal ; it is closed 

 inferiorly by a plate of cartilage, but its area is crossed by the internal 

 carotid artery and by the Vidian nerve. Behind the pars petrosa, and 

 bounded posteriorly by the jugular fossa of the occipital bone, is the foramen 

 jugulare, or foramen lacerum posterius : it is divided into a large external 

 and posterior part, bounded anteriorly by the jugular fossa of the temporal 

 bone, and occupied by the jugular vein; and a small anterior and inner 

 part, bounded by a portion of the pars petrosa distinct from the jugular 

 fossa, and transmitting the glosso-pharyngeal, vagus, and spinal accessory 

 nerves. The two parts of the foramen lacerum posterius are sometimes 

 completely separated by a spiculum of bone. Anterior to this opening is 

 the carotid foramen, external to it is the stylo-mastoid foramen and styloid 

 process, and internal to it is the anterior condyloid foramen. 



The posterior part of the inferior region presents on each side of the fore 

 part of the foramen magnum, in a transverse line outwards, the occipital 

 condyle, the rough surface for the rectus capitis lateralis muscle, the occi- 

 pital groove of the temporal bone, the digastric fossa, and the mastoid 

 process. Behind is the inferior division of the expanded part of the occipital 

 bone, with its ridges and muscular impressions. 



