58 



ANATOMY FOR NURSES 



[Chap. V 



T ZoM^UA^. 



the ethmoidal sinuses, wliich communicate with the nasal fossae. 



Descending from the horizontal plate on either side of the septum 



are two processes of 

 very thin, cancellous, 

 bony tissue, named the 

 superior and middle tur- 

 binated processes. 



Sphenoid bone. — It 

 is situated at the an- 

 terior part of the base of 

 the skull and binds the 

 other cranial bones to- 

 gether. It helps to form 

 tlie cavities of the cra- 

 nium, orbits, and nasal 

 fossae. In form it some- 

 what resembles a bat 

 ^ „„ ^ with extended wings, 



Fig. 29. — Parietal, Temporal, and Sphe- . -i j 



NOiD Bones. Posterior aspect. 1, body of sphe- and IS described aS COn- 



noid bone; 2, 2, preater wings of sphenoid bone; • j.' „ _f _ U^J,, +,,r„ 



3, 3, parietal bones ; 4, 4, mastoid process of tem- ^^^l^mg 01 a DOQJ , tWO 



poral bones. (Gould's Dictionary.) pairs of wiugS, and 



two pterygoid processes. 

 The body is joined to the ethmoid in front and the occipital be- 

 hind. It contains cavities which are called sphenoidal sinuses. 

 They communicate with the nasal fossae. 



THE SKULL AS A WHOLE 



The cranium is a firm case or covering for the brain. Four of the 

 eight bones which form this bony covering are classed as flat 

 bones. They consist of two layers of compact tissue, the outer 

 one thick and tough, the inner one thinner and more brittle. The 

 cancellated tissue lying between these two layers, or " tables of the 

 skull," is called the diploe. The base of the skull is much thicker 

 and .stronger than the walls and roof; it presents a number of 

 openings for the passage of the cranial nerves, blood-vessels, etc. 



The bones of the cranium begin to develop at a very early 

 period of fcetal life. Thus, before birth the bones at the top and 

 sides of the skull are separated from each other by membranous 

 tissue in which bone is not yet formed, and being then imperfectly 



