CHAP, in.] SKELETON OF THE HEAD AND TRUNK. 35 



familiarly known as the backbone, ribs and breastbone — and the 

 skeleton of tbe head, or cranial sJiekton. 



THE SPINAL SKELETON. 



As has been said, this consists of the backbone, together with certain 

 arches, the ribs, which extend from each side of a certain portion of 

 the backbone downwards to or towards the breastbone or sternum. 



§ 3. The backbone, or, as it is often called, the sjnne or spinal 

 column, consists of a number of small bones placed one behind the 

 other, like a series of counters. Each of these small bones is called 

 a VERTEBRA, and (with certain few exceptions, to be considered 

 later) consists of a bony arch projecting upwards from a solid disk — 

 the counter-like portion of the bone. Each whole vertebra may 

 thus be described as a ring much expanded at one part, which is 

 ihQ lower part, and with certain bony prominences, which stand out 

 from the bony ring in various directions. 



The vertebra} being, as has been said, placed one behind or in 

 front of the other, their juxtaposed rings together form a long 

 horizontal canal (ring being placed opposite ring), which is called 

 the rcrtchml canal. It is also called the neural canal, because it is 

 destined to contain and protect the central part of the nervous 

 system of the trunk, namely the spinal cord — or, as it is popularly 

 termed, the spinal marrow. 



The thickened inferior parts of the vertebrae are also adjusted one 

 in front of another, and by their juxtaposition form a solid but 

 flexible horizontal rod. 



§ 4. The thickened inferior part of each vertebra is called its 

 "body," or centrum (see Fig. 16) ; the ring of the vertebra springing 

 from the centrum is called, as before said, the neural arch. Each 

 lateral half of the neural arch consists of two parts : an inferior 

 rounded part called the pedicle, and a superior broad and flat 

 portion called the neural lamina. 



The various bony prominences of the vertebrae are termed 

 '' 2)rocesses" and at least three kinds of such processes are very 

 generally present. 



The first of these is the process which projects upwards from the 

 junction of the neural laminae at the summit of the neural arch. 

 This is the spinous process, neural spine, or neuropophysis. From the 

 junction of each lamina with its pedicle another process, ending 

 bluntly, juts outwards and upwards : this is called the transverse 

 process. Other processes which project more or less forwards and 

 backwards from the outer part of each lamina to meet corresponding 

 processes of adjacent vertebrae, are termed articular processes or 

 zygapophyses. 



Those projecting forwards have a smooth articular surface, which 

 looks mainly upwards, and are called anterior articular processes, or 

 prezyrjapophyses. 



D 2 



