26 



ANATOMY. 



a. The cavity of the skull, shown cut 

 through vertically in the middle line 

 in Fig. 9, has completely solid walls, 

 formed of the united bones of the cra- 

 nium. One of these bones, the frontal, 

 Fig. 8, 1, corresponds with the forepart 

 of the head (the frons, forehead), and 

 also forms the upper margin of the 

 sockets for the eyes ; two others, one 

 on each side, 2, called the parietal bones 

 (paries, the side), form the sides and 

 top of the skull ; other two, also exist- 

 ing in pairs, called the temporal bones, 

 3, correspond with the temples (tempus, 

 time) ; another single bone, which forms 

 the back of the head, is called the occi- 

 pital bone (ob and caput, the head) ; and 

 two other single bones, viz., the sphe- 

 noid or wedge-shaped bone, and the 

 ethmoid or sieve-like bone, complete the 

 base or floor of the skull, which is also 

 in part composed of the occipital and 

 temporals. All these bones are joined 

 together by their edges, which are un- 

 evenly toothed, or serrated, so that the 

 lines by which they meet, called the 



sutures of the skull, are more or less uneven or zigzag. It is also 

 obvious that the walls of the skull are put together after the manner 

 of an arch or vault. The cavity of the skull is lined throughout by a 

 tough membrane, called the dura mater, Fig. 9 c (hard mother), which 

 acts as a sort of internal periosteum, and also smooths off the asperi- 

 ties of the bony surface. The dura mater also sends off a vertical 

 partition downwards along the middle line, named, from its sickle- 

 shape, the /ate, /, which again falls behind on a transverse partition, 

 called the tentorium or tent. The interior of the dura mater is every- 

 where lined by a very thin, smooth, and moist membrane, belonging 

 to the serous membranes, and named the arachnoid (apa/vy, araclme, 

 a spider). From the back part of the base of the skull there extends 

 nearly the whole length down the centre of the spine or back-bone, a 

 secondary cavity, or rather a long canal, which is called the spinal or 

 vertebral canal. The upper part of this canal, s, and its continuity 

 with the cavity of the skull, which is effected through a large hole in 

 the occipital bone, called the occipital foramen (or hole), are clearly 

 seen in Fig. 9. It is lined by a tubular extension of the dura mater, 

 covered on its inner surface with the arachnoid membrane : the dura 

 mater does not here attach itself closely to the bones, which have their 

 proper periosteum distinct from it. The mode in which the bony canal 

 is formed is this. The spine, as already stated, consists of a' series of 

 bones called vertebrae, arranged in form of a column. There are in 

 the neck (cervix), Fig. 10, 1, seven of these bones, called cervical ver- 



Fig. 8. The bones of the head, which con- 

 gists of the cranium, and face ; 1, frontal 

 bone ; 2, left parietal bone ; 3, left temporal 

 bone ; 4, right upper jawbone ; 5, lower 

 jawbone ; 6, right cheek-bone. This figure 

 also shows the two eye-sockets or orbits, the 

 opening leading into the right and left 

 nasal or nose-cavities, and the arrangement 

 of the teeth in the jawbones. The cranium 

 has eight, and the face fourteen bones. 

 (From Nature.) 



