OSTEOLOGY AND SYNDESMOLOGY. 21 



stjlo-mastoid, mastoid, magnum, laccra postica, anterior and posterior 

 condyloid, aqueductus cochlea3, and the tympanic foramina in the petrous 

 bone. 



The inside of the skull {^jI. 121, fig. 5) is divided into the arch or vault, 

 and the base. On the vault is seen the sulcus for the longitudinal sinus, 

 the frontal crest, the grooves for the middle arteries of the dura mater, the 

 depressions for the convolutions of the brain and for the granulations or 

 glands of Pacchioni. The base of the skull is very uneven, and presents ou 

 each side of the median line three regions or fossae, on different planes, viz. 

 the anterior or frontal, the middle or spheno-temporal, and the posterior or 

 occipital. 



The anterior or frmital division is formed of the orbital plates of the 

 frontal bone, the cribriform plate of the ethmoid, and the lesser wings of 

 the sphenoid. The foramina are the coecum {fig. 5'), the olfactory {fig. 5^), 

 the internal orbital, and the optic (fig. 5 "). 



The middle or spheno-temporal division is bounded before by the lesser 

 wings of the sphenoid bone ; on the sides by the squamous portions of the 

 temporal, and behind by the superior angles of the petrous portions of the 

 same bone, and by the posterior clinoid processes of the sphenoid. In the 

 middle is the sella turcica ; on each side of, but below this, is a groove for 

 the carotid artery {fig. 5 '*), and below this is a shallow groove for the 

 superior maxillary nerve. Further out on each side are the cavities to 

 lodge the middle lobes of the brain, and on the superior surflice of the 

 petrous bones are seen the juttings of the vertical semicircular canals. 

 ^e foramina in this division are, the foramina lacera orhitalia superiora, 

 rotunda {fi^. 5"), ovalia {fig. 5'^), carotica {fig. 5"), spiaalia {fig. 5'°), lacera 

 basis cranii anteriora, and innorninata or hiatus Fallopii. 



The posterior or occipital region is bounded before by the basilar process 

 and by the posterior surface of the petrous bones, and behind by the 

 occipital ; it presents the basilar process, the foramen magnum, and the 

 perpendicular ridge of the occipital crossed by the transverse, by which 

 this bone is divided into four fossce. On the superior angle of each petrous 

 bone is a shallow groove for the superior petrosal sinuses; the transverse 

 occipital ridge presents a deep groove for the lateral sinuses, which last are 

 continued over the inferior angles of the parietal bones, and thence descend 

 inwards along the mastoid portions of the temporal bones, and then again 

 groove the occipital, passing forwards on it to the posterior foramina lacera. 

 The perpendicular ridge is grooved above for the longitudinal sinus, which 

 terminates sometimes in the left, but more frequently in the right lateral 

 sinus. The vertical ridge below the tentorium gives attachment to the falx 

 minor, and is slightly grooved for the occipital sinuses. The foramina in 

 this division are, the foramina auditoria interiora {fig. 5 ^°), the aqueductua 

 vestihuhrum, foramina lacera postica.^ foramen magnum, foramina condyloüitjf 

 antica {fig. 5"), Sind postica {fig. 5"). 



727 



