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OG'CIPITAJ, BONE. 



Fig. 23.' 



basilar portion of the bone is the foramen magnum, oblong in form, and 

 larger behind than before, transmitting the spinal cord, spinal accessory 



nerves, and vertebral arteries. Upon 

 the lateral margins of the foramen 

 magnum are two rough eminence's, 

 which give attachment to the odon- 

 toid ligaments, and immediately above 

 these the openings of the anterior con- 

 dyloid foramina. In front of the fora- 

 men magnum is the basilar process, 

 grooved on its surface, for supporting 

 the medulla oblongata, and along each 

 lateral border, for the inferior petrosal 

 sinuses. On each side of the foramen 

 magnum is a groove, for the termina- 

 tion of the lateral sinus ; a smooth sur- 

 face, which forms part of the jugular 

 fossa; and a projecting process, which 

 divides the two, and is called the 

 jugular eminence. Into the jugular 

 fossa will be seen opening the posterior condyloid foramen. 



The superior borders are very much serrated, and assist in forming the 

 lambdoidal suture ; the inferior are rough, but not serrated, and articulate 

 with the mastoid portion of the temporal bone by means of the p'ldita- 

 mentum sutura? lambdoidalis. The jugular eminence and the side of the 

 basilar process articulate with the petrous portion of the temporal bone, 

 and the intermediate space, which is irregularly notched, forms the poste- 

 rior boundary of the jugular foramen, or foramen lacerum posterius. 



The angles of the occipital bone are the superior, inferior, and two 

 lateral. The superior angle is received into the interval formed by the 

 union of the posterior and superior angles of the parietal bones, and cor- 

 responds with that portion of the foetal head which is called the posterior 

 fontanelle. The inferior angle is the articular extremity of the basilar 

 process. The lateral angles at each side project into that interval formed 

 by the articulation of the posterior and inferior angle of the parietal with 

 the mastoid portion of the temporal bone. 



Development. By seven centres ; four for the four parts of the expanded 

 portion divided by the crucial ridge, one for each condyle, and one for 

 the basilar process. Ossification commences in the expanded portion of 

 the bone at a period anterior to the vertebraB ; at birth the four remaining 

 pieces are distinct; they are united at about the fifth or sixth year. After 

 twenty the basilar process unites with the body of the sphenoid. 



*The internal surface of the occipital bone. 1. The left cerebral fossa. 2. The left 

 cerebellar fossa. 3. The groove for the posterior part of the superior longitudinal sinus. 

 4. The spine for the falx cerebelli, and groove for the occipital sinuses. 5. The groove 

 Tor the left lateral sinus. 6. The internal occipital protuberance, the groove on which 

 lodges the torcular Herophili. 7. The foramen rnagnurn. 8. The basilar process, 

 grooved for the medulla oblongata. 9. The termination of the groove for the lateral 

 sinus, bounded externally by the jugular eminence. 10. The jugular fossa; this fossa 

 is completed by the petrous portion of the temporal bone. 11. The superior border. 

 12. The inferior border. 13. The border which articulates with the petrous portion of 

 the temporal bone, and which is grooved by the inferior petrosal sinus. 14. The anve 

 rior condy'oid foramen. 



