146 DORSAL VERTEBRA. 



The TWELVE DORSAL may be distinguished from the other 

 vertehrfB of the spine by the following marks. 



Their bodies are of a middle size, between those of the neck 

 and loins. They are more convex before than either of the 

 other two sorts ; and are flattened laterally by the pressure 

 of the ribs, which are inserted into small cavities formed in 

 their sides. This flatness of their sides, which makes the figure 

 of these vertebras almost a half oval, is «of great use ; as it 

 affords a firm articulation to the ribs, allows the tracheal tube 

 to divide at a small angle, and the other large vessels to run 

 secure from the action of the vital organs. Their bodies are 

 more concave behind than any of the other two classes. The 

 upper and lower surfaces are horizontal. 



The cartilages interposed between the bodies of these verte- 

 brae are thinner than in any other of the true vertebra ; and 

 contribute to the concavity of the spine in the thorax, by being 

 thinnest in their forepart. 



The oblique processes are placed almost perpendicularly : 

 the upper ones slanting but a little forwards, and the lower 

 ones slanting as much backwards. The convexity or concavity 

 is not so remarkable as to require particular notice. Between 

 the oblique processes of opposite sides several sharp processes 

 stand out from the upper and lower parts of the plates which 

 join to form the spinous processes : into these sharp processes 

 stroncr lifjaments are fixed for connecting the vertebrae. 



The transverse processes of the dorsal vertebras are long, 

 thicker at their ends than in the middle, and turned obliquely 

 backwards, which may be owing to the pressure of the ribs ; 

 the tubercles of which are inserted into a depression near the 

 end of these processes. 



The spinous processes are long, small-pointed, and sloping 

 downwards and backwards. From their upper and back 

 part a ridge rises, which is received by a small channel in the 

 forepart of the spinous process immediately above, which is 

 here connected to it by a ligament. 



The canal for the spinal marrow is here more circular, but 

 corresponding to the size of that chord, is smaller than in any 



