RESPIRA TION 



IO»' 



would not form a joint with the spine ; but it may be suggested 

 that this series of joints is of far more importance in securing 

 flexibility of the spine than in respiratory functions, while the 

 method by which they articulate shows that they are propping 

 the spine up — a feature which is in marked contrast to the false 

 ribs. If the true ribs be examined, it will be found that both 

 the head and tubercle are large and well developed, the tubercle 

 being disposed above the head (Fig. 41. A), and both so arranged 

 towards the vertebrae that they prop it up. From the first to 

 the seventh rib the substance and strength of rib is very 

 evident ; from the eighth backwards the ribs decrease in size, 

 both in width and depth, and the decrease in substance becomes 

 progressively greater. From the first to the thirteenth rib the 



Fig. \z. — Vertical Section of the Body through the Eighth and 

 Seventeenth Dorsal Vertebrae. 



A, Eighth dorsal ; B, seventeenth dorsal section. 



tubercle is above the head, but from the fourteenth backwards 

 the tubercle is placed lower and lower, and finally is in the same 

 horizontal plane as the head (Fig. 41, B). The tubercle begins to 

 descend from the time the ribs are so far removed from the 

 sternum, that no further propping up of the spine is possible. 



The narrowness of the anterior part of the thorax is to accom- 

 modate the fore-legs, which are, as it were, plastered on to it. 



The false ribs have no sternal insertion, but each one is con- 

 nected to the one in front by means of a piece of cartilage ; while 

 rigidity of the walls is characteristic of the anterior chest, mobility 

 is characteristic of that portion now being considered. The false 

 ribs are narrow, thin, and curved. The curve gives the barrel 

 shape to the side of the chest. Further, these ribs before they 

 curve downwards have a relatively level or flat surface on their 



