OSTEOLOGY AND SYNDESMOLOGY. 21 
stylo-mastoid, mastoid, magnum, lacera postica, anterior and _ posterior 
condyloid, aqueductus cochlez, and the tympanic foramina in the petrous 
bone. 
The inside of the skull (pl. 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 on 
each side of the median line three regions or fossee, on different planes, viz. 
the anterior or frontal, the middle or spheno-temporal, and the posterior or 
occipital. 
The anterior or frontal 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 ccecum (jig. 5"), the olfactory (jig. 5°), 
the internal orbital, and the optic (jig. 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 
supericr maxillary nerve. Further out on each side are the cavities to 
lodge the middle lobes of the brain, and on the superior surface of the 
petrous bones are seen the juttings of the vertical semicircular canals. 
The foramina in this division are, the foramina lacera orbitalia superiora, 
rotunda (fig. 5"), ovalia (fig. 5"), carotica (fig. 5”), spinala (fig. 5”), laceru 
basis cranw antervora, and innominata or hiatus Fallopi. 
The posterior or occipital region 1s 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 fossee. 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 ig 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 shghtly grooved for the occipital sinuses. The foramina in 
this division are, the foramina auditoria interiora (fig. 5*°), the aqueductus 
vestibulorum, foramina lacera postica, foramen magnum, foramina condyloide 
antica (fig. 5), and postica ( fig. 5**), 
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