BY W. J. McKAY. 903 



anticus, which is also inserted on the posterior half of the inferior 

 surface of the bone. The sacro-lumbalis prolonged forward from 

 the dorsal region is also attached to the lateral spines. The superior 

 surface is deeply excavated to receive the medulla. The basi- 

 occipital articulates with the basisphenoid, exoccipital, and 

 proptic. 



Os EXOCCIPITALE. 



Pars lateralis ossis occijyitis, D'Alton ; Occijntalia lateralia, 

 Cuvier, Gegenbaur, Kallmann, Harting, Joh. Miiller, Owen, Stan- 

 nius, Hoffmann, Wiedersheim ; JSxoccipitale, Huxley, Parker and 

 Bettany, Parker ; Gelenkstilck des Hinterhauptbeins, Meckel j 

 Schenkel des Hinterhauptbeins, Rathke. 



The exoccipitals are irregularly shaped bones which bound in 

 great part the foramen magnum. Each bone consists of a superior 

 horizontal, and a vertical lateral piece. The upper face of the 

 superior piece is flattened and gives attachment to the spinalis dorsi, 

 complexus, and trachelo-mastoideus. The anterior border articu- 

 lates with the supraoccipital, the mesial border with its fellow of the 

 opposite side, while the external is raised into a prominent edge 

 to join the opisthotic, and gives attachment to some of the fibres of 

 origin of the digastric muscle. The vertical or lateral plate presents 

 a small tubercle for the attachment of the trachelo -mastoid, while 

 immediately beneath this there is a second tubercle for the superior 

 part of the rectus capitis anticus. The internal surface of this 

 plate is in contact with the medulla. Four foramina may be seen 

 on the surface. The anterior three lie in the same line, and 

 transmit the ninth, tenth, and twelfth nerves; the fourth is placed 

 superiorly and posteriorly, and is the " posterior condyloid fora- 

 men" (Parker). The anterior border articulates with the 

 opisthotic, and slightly with the prootic, the inferior with the 

 basioccipital, while the posterior runs downwards and backwards 

 and goes to make up the occipital condyle by being the superior 

 moieties of the trefoil-shaped surface. The foramen magnum is 

 bounded almost entirely by these bones, the basioccipital supplying 

 the lower portion only. 

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