LECTURE II. — Tuesday, May 2>oth, 187 1. 



Geometrical Classification of Muscles found in Animals. — Application of 

 the principle of Least Action to several foriiis of Muscle, demonstrating 

 the possibility of predicting^'' Animal Structures by Mathematical 

 Calculations similar to those used in Astronomy and the other exact 

 Sciences. — Special Illustrations from the Limbs of the Tiger and Wings 

 of the Albatross. 



In bringing to a conclusion my former lecture, I acted on the principle 

 that I laid down of the "least action." Taking into consideration the 

 feelings of the audience as well as of the lecturer, and judging by my 

 own experience in hearing sermons and lectures, I thought that some- 

 what less than an hour's lecture v/ould suit your tastes. I therefore 

 threw overboard one interesting application of the principle of least 

 action in order to lighten the ship, and bring her safely into harbour ; 

 but if it is your pleasure that I should now state the problem of the 

 tendons of the fore and hind limbs of animals, which I omitted to state 

 in my last lecture, I place myself in your hands ; but you will have 

 yourselves to blame if we do not carry out perfectly the principle of 

 minimum trouble and least action by this rash proposal. 



I hold in my hand the flexor tendon of the hind leg of the eland. 

 You will observe that at one extremity it branches into three distinct 

 tendons, and at the other extremity it divaricates into two. These 

 three tendons are the connecting ropes that join the common tendon in 

 the foot with the three great muscles of the leg that act upon it. Three 

 streams of force enter the common tendon through these three different 

 lines, and they are then distributed by the intervention of this divari- 

 cating tendon into two ; these two applications of force are carried to 

 the toes of the animal. Somewhat similar arrangements are found in 

 the fore limb and hind limb of almost every animal. We have the 

 muscles acting at one extremity of the tendons, which are the connect- 

 ing ropes that join the muscular forces with their points of application; 

 and we have these both in the fore and in the hind limb. Now, in the 

 case of many animals the fore limb and the hind limb are always used for 

 the same purpose. In the case of the llama, the horse, and the cow, 

 the fore limb and the hind limb have scarcely any different functions : 

 the animals are, in the strictest sense of the word, quadrupeds ; their 

 fore feet are used simply for the purposes of locomotion. But in the 

 higher classes of animals, like tigers, cats, bears, dogs, monkeys, and 



