GENEKAL CHAEACTERS OF THE VEETEBEATA. 201 



and whicli are known as the radius and ulna {r and m), of 

 which the former is the bone mainly concerned in carrying the 

 hand or fore-foot. 4. A number of small bones, which form 

 the wrist, and are termed the carpus (df). 5. The cylindrical 

 bones (usually five in number) which form the root of the 

 hand, and are known as the metacarpus (m). 6. The bones 

 which form the fingers proper, and which are known as the 

 phalanges [p). 



Essentially the same parts can be traced in the hind-limb 

 of a typical Vertebrate animal, but they are known by differ- 

 ent names. The bones which unite the limb to the trunk are 

 usually more or less completely united together, constituting 

 a single mass, known as the innominate hone (Fig. 97, i). 

 This is followed by a long, cylindrical bone, which forms the 

 upper portion of the hind-limb, and is known as the " thigh- 

 bone," or femur (f). Following this are the two bones of 

 the shank, corresponding to the radius and ulna of the fore- 

 limb, and known as the tibia and fibula (t and s). Qi these, 

 the tibia (t) corresponds to the radius, and is mainly con- 

 cerned in carrying the foot. Next comes a series of small 

 bones, which form the ankle, and are known as the tarsus {r). 

 This is succeeded by a series of cylindrical bones (usually five in 

 number), which form the root of the foot, and which are termed 

 the metatarsus (m). Finally, the metatarsus is succeeded 

 by the bones of the toes, which in this case are again termed 

 the phalanges {p). In both limbs the usual number of pha- 

 langes to each toe or " digit " is three. 



The digestive system of the Vertebrata does not require a 

 lengthened notice. The mouth is usually furnished with teeth, 

 which have for their chief function the reduction of the food 

 to a condition in which it can be digested. In some animals, 

 however, such as the snakes, the teeth are only used to hold 

 the prey, and not for mastication ; and in others, such as the 

 turtles and birds, the jaws are not furnished with any teeth 

 at all. The food is also usually subjected in the mouth to the 

 action of a special fluid — the saliva — which acts chemically as 

 well as mechanically upon the food, and which is secreted by 

 special glands, known as the " salivary glands." From the 

 mouth the food passes through a muscular tube — the gullet, 

 or oesophagus (Fig. 98, g) — to the proper digestive cavity, or 

 stomach (s). Here it is subjected to the action of a special 

 digestive fluid — the " gastric juice " — and is converted into a 

 thick, pasty fluid, which is called chyme. From the stomach 

 the chyme passes into a long, convoluted, muscular tube, which 



