208 ELEMENTARY BIOLOGY. [XITI. 



together in the adult: the following points can 

 however be made out with tolerable ease. Drawings 

 should be made of each aspect of the skull. 



1. Examine the posterior end of the skull. 



a. The large aperture (foramen magnum) in the 

 middle line, leading into the cranial cavity. 



b. The convex surface (occipital condyle), on each 

 side of the foramen magnum, which articulates 

 with the corresponding concave facet on the 

 front of the atlas. 



c. The bone bearing the condyle on each side and, 

 with its fellow, enclosing the foramen magnum, 

 is the exoccipital, 



d. The thick bone running outwards in front of the 

 exoccipital, on each side, protects the front part of 

 the internal ear, and is the pro-otic bone. 



e. Between these two bones, on the outer side of the 

 chamber which contains the organ of hearing 

 (periotic capsule.,) is a cartilaginous interspace 

 containing an oval aperture, the fenestra ovalis. 

 In this is fixed the inner end of a partly carti- 

 laginous and partly osseous rod, the columella 

 auris. 



f. Attached to the outer end of the pro-otic bone is 

 a hammer-shaped bone the squamosal, which 

 extends from the pro-otic bone to the articulation 

 of the lower jaw, 



2. The roof of the skull 



a. Passing forwards from the exoccipitals are two 

 long flat bones, the parieto-frontals, one on each 



