' OSTEOLOGY. 13 



The internal surface is irregularly concave and divided by 

 a crucial ridge, or occipital cross, into four fossae, the upper, for 

 the posterior lobes of the cerebrum, and the lower, for the lateral 

 lobes of the cerebellum. Its centre is marked by an eminence, 

 the internal occipital protuberance, which is hollowed out to 

 correspond to the torcular Herophili, or confluence of the sinuses. 



The upper division of the crucial ridge affords attachment 

 for the falx cerebri, being grooved for the great longitudinal 

 sinus; the lower extremity, called also the internal occipital 

 crest, affords attachment for the falx cerebelli, being grooved 

 for the occipital sinus; and the lateral divisions afford attach- 

 ment for the tentorium cerebelli and are grooved for the lateral 

 sinuses. 



The internal surfaces of the jugular processes are grooved 

 for the lateral sinuses. 



In front of the foramen magnum is the basilar groove, 

 lodging the medulla oblongata and part of the pons Varolii. Its 

 lateral borders (the basilar process) are grooved for the inferior 

 petrosal sinus. 



The superior angle articulates with the parietal bones, the 

 inferior angle articulates with the sphenoid, and the lateral 

 angles are wedged in between the mastoid portion of the tem- 

 poral and the posterior inferior angle of the parietal. 



This bone has four foramina foramen magnum, anterior 

 and posterior condyloid, and foramen lacerum posterius. 



It articulates with six bones two parietal, two temporal, 

 the sphenoid, and the atlas. 



The muscular attachments are twelve (12) : occipito-fron- 

 talis, trapezius, sterno-mastoid, complexus, splenius capitis, ob- 

 liquus superior, rectus capitis, posticus major and minor, rectus 

 lateralis, rectus anticus major and minor, and superior pharyn- 

 geus constrictor. 



It is developed from seven (7) ossific centres: four for 

 the tabular, or supra-occipital, or occipital portion proper; one 

 for each condyloid, or external occipital portion, and one for the 

 basilar, or basi-occipital portion. 



TEMPORALS. These are situated at the side and base of the 

 cranium, and consist of three portions the squamous, mastoid, 

 and petrous. 



The squamous portion is scale-like and overlaps the parietal 

 bono. Its external surface, convex behind, concave in front, pre- 

 sents from before backward the following: 



The zygoma, or zygomatic process, an arched process of 

 bone articulating with the zygomatic process of the malar bone, 

 and affording attachment above to the temporal fascia and below 



