420 GRACE A. WELLS 



passage of the spinal cord, is visible from above at the posterior 

 end of the cranium. It lies in the median line, somewhat in ad- 

 vance of the lateral occipital region (to be described later). A 

 little in front of the foramen magnum, a pit — the fossa endo- 

 lymphaticus {J. end.) contains the external openings of the endo- 

 lymph ducts (e.d.). This pit is deepest behind, its boundary 

 curving forward from the posterior side of the fossa until it 

 becomes parallel with the axis of the cranium, gradually fading 

 out just inside the sulcus longitudinalis of either side. The fora- 

 mina for the endolymph ducts occur, one on either side, close to 

 the wall of the fossa at about the middle of its antero-posterior 

 extent. A little behind these, there is, on either side, a larger 

 opening for the perilymph duct (per d.), close to the postero- 

 lateral curvature of the fossa. 



Behind the posterior wall of the fossa endolymphaticus, the 

 dorsal surface of the cranium slopes obliquely downward and 

 back to the hinder margin of the cranium, this basal surface 

 being nearly as much vertical as dorsal. From the posterior 

 wall of the endolymph fossa a ridge, the crista occipitalis (c.o.), 

 extends in the median line back to the anterior (superior) mar- 

 gin of the foramen magnum. 



In the view from above, the posterior margin of the cranium 

 is irregular in outline. Behind and below the foramen magnum 

 is the depression where the centrum of the first vertebra artic- 

 ulates with the cranium and on either side of this is a some- 

 what triangular occipital condyle (o.c.) which articulates with 

 the corresponding side of the centrum. Lateral to each con- 

 dyle the posterior margin has an arcuate excavation, the outer 

 border of this being formed by the postero-lateral angle of the 

 cranium. 



On the roof of either otic capsule, between the fossa endo- 

 lymphaticus, the postero-lateral angle and the postorbital 

 process are ridges indicating the position of the semicircular 

 canals of the ear, within the capsule. One, over the posterior 

 canal, (p.c.) extends from the postero-lateral margin of the fossa 

 endolymphaticus outwards and backwards, fading out near the 

 postero-lateral margin of the cranium. The other, covering the 



