48 



CLASSIFICATION 



side of the backbone, and from each of them a tube, the 

 ureter, conducts the products of waste to a good -sized bag, 

 the urinary bladder, which is sheltered in the cavity of the 

 pelvis and opens to the exterior. 



4. The Liver.— Nitrogenous waste is got rid of chiefly by 

 the liver and kidneys. The liver, which has already been de- 

 scribed as a digestive gland, is also a waste -eliminating organ, 

 for bile is a waste product as well as a digestive juice. 



ORGANS OF MOVEMENT. 



I. Muscular Action. — The obvious movements of the body 

 are brought about by the masses of flesh technically known as 

 muscles, which make up a large proportion of its weight. These 

 muscles are of various shapes, in accordance with 

 ''111/ A "-'^^ differences in their uses; but they all agree in 

 t J \\ ' ^'"& composed of vast numbers of microscopic 

 - ' iibres which, under the control of the nerves, are 

 ble to contract, i.e. to shorten, while at the same 

 I 'me they become broader. The result is, that the 

 parts to which the ends of an elongated muscle are 

 fixed are brought nearer together. Such a muscle 

 is generally attached at one end (the origin) to a 

 relatively fixed part, and at the other (the insertion) 

 to a relatively movable part. This is the case, for 

 example, with the biceps muscle, easily felt as a 

 mass of flesh on the front of the forearm (fig. 24). 

 This takes origin from the scapula and is inserted 

 into the radius, the result being that when it con- 

 tracts, the forearm, being the relatively movable 

 part, is drawn up. 



Muscles are commonly attached by means of 

 firm fibrous cords, the tendons, an arrangement 

 which permits a large number of muscles to be 

 attached to a small part, such as a finger-bone, and 

 further permits such muscles to act from a considerable distance. 

 The use of skeletal parts in giving attachment to muscles is 

 obvious, and the numerous ridges and projections seen on bones 

 are largely related to this function. 



Muscle is also important in relation to the movements of 



Fig. 24. — Biceps 

 Muscle of the Arm 



BS; Fleshy part; 00', 

 origin; i, insertion. 



