i:j() THE CAT. [CHAP. v. 



known in mechanics. A " lever " consists of a rigid rod, movable 

 in one plane round a point the " fulcrum." 



The first order of levers is where the fulcrum is placed between 

 the weight and the motive power. 



The second order is "where the iveight to he moved (or resistance 

 to be overcome) is placed between the fulcrum and the power. 



The third order is where the power is applied between the fulcrum 

 and the weight or resistance. 



In the action of the hind-legs of a cat which is lying on its back 

 and scratching at an object with its hind claws, we have an example 

 of the first order of levers. For thus the muscles of the calf, being 

 attached to the tuberosity of the os calcis, act on the skeleton of the 

 foot as on a rod resting against the distal end of the tibia as on a 

 fulcrum. The other end of this rod (the claw-bearing part) pushes 

 away any object against which it may strike. 



The same parts, as employed in walking, may serve as an example 

 of the second class of levers. Thus considered, the earth will be 

 the fulcrum, the weight to be moved (the body as resting on the 

 tibia) being placed between it and the point of muscular attachment 

 that is where the motive power is applied. 



An example of the third order of levers is seen in the action of the 

 cat in raising the fore-paw to strike or to wash the face or ear. Here 

 the paw is the weight, and the fulcrum is the distal end of the humerus. 

 The motive-power being applied in the intermediate space, viz. (as we 

 shall see) at the attachment of the biceps muscle to the radius. 



6. The CLASSIFICATION of muscles follows naturally that of the 

 parts of the skeleton. Thus we have 



(a) Muscles of the exo-skeleton, the skin, and 



(b) Muscles of the endo-skeleton. 



To these it will be convenient to add a third categoiy, namely, 



(c) Muscles of the viscera. 



The exo-skcletal system of muscles may consist of smooth or striped 

 fibres. Some are large and some very small. 



The endo-skeleta! system is naturally divisible, like the endo- 

 skeleton itself, into parts appertaining to the head, trunk, and tail 

 (the axial portion), and parts belonging to the limbs (the appen- 

 dicular portion). 



The viscero-skeletal system of muscles consists of the muscular 

 fibres placed in the walls of the alimentary canal and in a variety of 

 tubes or organs (such as the heart, bladder, &c.,) to be hereafter 

 noticed in describing those parts. 



Since, however, the muscles of the first category are few in 

 number, while those of the third may be better considered in treat- 

 ing of the viscera they help to form, the best practical course here 

 will be to consider the muscles according to the regions of the body 

 to which they belong the head and neck, the trunk and tail, and 

 the limbs. 



