protuberances, D D, by which the head is connected with the alias, or upper, 

 or first vertebra, or bone of the neck, and these are called the condyloid, 

 cup-shaped, processes of the occipital bone. All the motions of the head are 

 partly, and many of them wholly, performed by this joint. 



Between them is a large hole, called the foramen magnum, or great 

 aperture, E, through which the continuation of the brain, called the spinal 

 cord or marrow, passes out of the skull. 



As an additional contrivance to support the great weight of the head, are 

 two other projections of the occipital bone, jjeculiar to animals whose heads 

 are set on in a slanting direction, and into which powerful muscles are 

 inserted ; they are called the ceracoid, beak-like, processes or prolongations, 

 F F, of ihe occipital bone. 



Runnmg forward, and forming outwardly a part of the base, and inwardly 

 a portion of the floor of the skull, is what, from its wedge-like shape, is 

 called the cuneiform process of the occipital bone (fig. i, p. 68). It is thick, 

 strong and solid ; and placed at the bottom of the skull, not only to be a 

 proper foundation for, and to give additional strength to the arch on each 

 bide, but speedily to break and stop all vibration and concussion. 



At the base of the skull, and anterior to, or below the occipital, lies the 

 sphenoid, wedge-like bone (fig. k, p. 68). Its body, likewise called the 

 cuneiform or wedge-shaped process, is a continuation of the same process of 

 the occipital, and like it is thick and solid, and for the same important 

 purpose. This bone branches out into four irregular bodies or plates, two 

 of which are called the wings, and two running to the palate, the legs. 

 They could not be represented in the cut, and there is nothing important 

 belonging to them so far as our work is concerned. Internally (fig. A), the 

 sphenoid forms a portion of the cavity of the skull. 



Of the ethmoid, sieve-like, bone little can be seen outwardly. A small 

 portion is found in the back part of the orbit, and in the cavity of the cra- 

 nium ; but the most important part of it is that which is composed of a 

 great number of thin plates, forming numerous cavities or cells (fig. /, p. 68) 

 lined with the membrane of the nose, and entering into the cavity of the 

 nose. The upper portion is called the cribriform, or sieve-shaped plate, 

 from its being perforated by a multitude of little holes, through which the 

 nerve connected with the smelling passes and spreads over the nose. 



Altogether, lliese bones form a cavity of an irregular oval shape, but the 

 tentorium penetrating into it, gives it the appearance of being divided into 

 two {d, p. 68). 



The cavity of the cranium may be said to be arched all round. The 

 builder knows the strength which is connected with the form of the arch. 



