122 



OSTEOLOGY. 



either side of the foramen magnum ; on their inferior surfaces they bear 

 the occipital condyles by means of which the skull articulates with the atlas. 

 Of elongated oval form, the condyles are so disposed that their anterior 

 extremities, in line with the anterior margin of the foramen magnum, lie closer 

 together than their posterior ends, which extend as far back as the middle 

 of the lateral borders of the foramen. Convex from before backwards, they 

 are skewed so that their surfaces, which are nearly plane from side to side, are 

 directed slightly laterally. Each is supported on a boss of bone, pierced by the 

 canalis hypoglossi (hypoglossal canal), which opens obliquely from within outwards 

 and forwards on the floor of a fossa, situated just lateral to the anterior part 

 of the condyle. The canal transmits the hypoglossal nerve, together with 

 a meningeal branch of the ascending pharyngeal artery and its companion 



Highest nuchal lin 



External occipital protuberance 



Superior nuchal line 



Inferior 

 nuchal., 

 line > 



Canalis condy- 

 loideus 



Jugular process 



Jugular notch 



Condyle 

 Pharyngeal tubercle 



FIG. 133. THE OCCIPITAL BONE AS SEEN FROM BELOW. 



veins. Behind the condyle is placed the fossa condyloidea, in the floor of which 

 the canalis condyloideus (condyloid canal) frequently opens. Through this a 

 vein passes which joins the transverse sinus. The fossae lodge the posterior 

 margins of the superior articular processes of the atlas in extension of the head. 

 The edge of the foramen magnum immediately posterior to the condyle is often 

 grooved for the passage of the vertebral artery around it. Jutting laterally 

 from the posterior half of the condyle is a stout bar of bone, serially homologous 

 with the vertebral transverse processes ; this is the processus jugularis ; deeply 

 notched in front (jugular notch) its anterior border is free and rounded, and 

 forms the posterior boundary of the jugular foramen. Curving laterally from this 

 margin, in line with the hypoglossal canal, there is often a small pointed projection, 

 the processus intrajugulare, which serves to divide the jugular foramen into two 

 compartments. Laterally, the jugular process articulates by means of a synchon- 

 drosis with the jugular surface of the petrous part of the temporal bone. Its 

 posterior border is confluent with the inferior and lateral portion of the occipital 

 squama, and its under surface is rough and tubercular for the attachment of the 



