XVI] IN THE SKELETON OF QUADRUPEDS 703 



constitutes a great portion of the posterior cantilever arm, or 

 even its chief portion in cases where the size and weight of the 

 tail are insignificant, as is the case in the majority of terrestrial 

 mammals. 



We may also note here, that just as a bridge is often a 

 "combined" or composite structure, exhibiting a combination of 

 principles in its construction, so in the quadruped we have, as 

 it were, another girder supported by the same piers to carry the 

 viscera ; and consisting of an inverted parabolic girder, whose 

 compression-member is again constituted by the backbone, its 

 tension-member by the line of the sternum and the abdominal 

 muscles, while the ribs and intercostal muscles play the part of 

 the web or filling. 



A very iew instances must suffice to illustrate the chief 

 variations in the load, and therefore in the bending-moment 

 diagram, and therefore also in the plan of construction, of various 

 quadrupeds. But let us begin by setting forth, in a few cases, 

 the actual weights which are borne by the fore-limbs and the 

 hind-limbs, in our quadrupedal bridge*. 



It will be observed that in all these animals the load upon the 

 fore-feet preponderates considerably over that upon the hind, the 

 preponderance being rather greater in the elephant than in the 

 horse, and markedly greater in the camel and the llama than in 

 the other two. But while these weights are helpful and sug- 

 gestive, it is obvious that they do not go nearly far enough to 

 give us a full insight into the constructional diagram to which 

 the animals are conformed. For such a purpose we should 



* I owe the first four of these determinations to the kindness of Dr Chalmers 

 Mitchell, who had them made for me at the Zoological Society's Gardens ; while 

 the great Clydesdale carthorse was weighed for me by a friend in Dundee. 



