26 ELEMENTARY ANATOMY. [LESS. 



posterior cylinder of the human trunk, spoken of in the First 

 Lesson. 



The thickened anterior parts of the vertebras are also 

 placed and adjusted one upon another, and by their super- 

 position form a vertical solid column, namely, that spoken 

 of in the first lesson as the partition separating the small 

 dorsal cylinder from the larger ventral one. 



The thickened anterior part of each vertebra is called 

 its " body " or " centrum." The ring of the vertebra (which 

 springs from the centrum on each side of its posterior surface 

 meeting in the middle line behind) is termed the arch and, 

 because it contains part of the spinal cord, the neural r 

 arch the spinal cord being, with the brain, the central part of 

 the nervous system. 



The various bony prominences of the vertebras are termed 

 " processes." 



The vertebrae are connected by joints of the second (or 

 mixed) kind. Their adjacent surfaces are for the most part 

 nearly flat, and we find interposed and connecting them a 

 dense fibrous body or disc, toughest and hardest towards its 

 circumference, with a pulpy substance in its middle. Each 

 such body is termed an intervertebral substance. No syno- 

 vial fluid lubricates the joints between the bodies of the 

 vertebrae, though present between the junctions of some of 

 the processes. 



The vertebras are also held together by strong ligaments 

 which pass vertically down the centra, both in front of and 

 behind them. 



7. The VERTEBRA are divisible into five different categories. 



First come those of the neck, which are termed cervical? 

 They are seven in number. 



Secondly, those of the back, which have the ribs attached 

 to them, and which bear the name dorsal. Of these there 

 are twelve. 



Thirdly, we find certain large vertebras which do not 

 bear ribs : these are situate below the dorsal vertebrae, and 

 are called lumbar. There are five of them. 



All the above vertebrae are termed " true vertebras," 

 because they do not become anchylosed together, but remain 

 connected by ligaments and by intervertebral substances only. 



Below these true vertebras come those which are called 

 "false," and which sooner or later anchylose together to form 

 two bony masses. 



1 From i/eupoi/, a nerve. - From cervix, the neck. 



