396 ZOOLOGY. 



lating surfaces, there being no ribs connecting with them. The vertebrae 

 which follow the abdominal ones are soldered together, and constitute the 

 quadrangular ossa sacra, or sacrum, concave below and convex above. 

 Their number is generally very restricted, and varies within narrow limits. 

 The vertebral column terminates by the vertebrae of the tail, which in their 

 form and number differ greatly from the others. The first ones still possess 

 the canal for the spinal maiTOW, but it vanishes gradually ; and the last of 

 the series consists of a cylindrical or prismatical body, more or less elongated, 

 with rudimentary apophyses, or completely deprived of them. 



The ribs correspond in number to the dorsal vertebrae ; they are elongated 

 and curved cylindrical, prismatical, or compressed bones, without lateral 

 processes, and never immediately connected with the breast bone below. 

 The breast bone itself is composed of numerous cylindrical or compressed 

 pieces, situated behind each other, with which the true ribs are united by 

 means of cartilages. The others, or false ribs, are situated behind the 

 breast bone ; are always shorter, and are connected together by cartilagi- 

 nous pieces. 



Most of the mammals are provided with four legs ; the hind pair consist- 

 ing of a thigh, a shank, a tarsus, and a foot ; the fore pair, of an arm, a fore 

 arm, a wrist, and a hand. The fore legs are generally shorter than the hind 

 ones, and usually bent a little inwards; but, again, in some they are so 

 short, and the hind so long, that when the animal attempts to walk on four 

 legs, the anterior part of the body is much lower than the posterior part, 

 even though the hind legs be considerably bent. Hence, it results that 

 these animals, as kangaroos, &c., prefer jumping or running on the hind 

 legs alone. The opposite development of the legs, or the presence of 

 fore legs longer than the hinder, is observed in the Asiatic orang outang, in 

 the long-armed monkey, the sloth, 6tc. In the bat, also, the fore legs, or 

 rather the fingers, are very long, and between them and the hind legs the 

 skin of the body is extended, so that by this means these animals can 

 keep on the wing. In others the skin is less expanded, and serves only as a 

 parachute, and not for the real act of flying. Mammals walk either on the 

 toes alone, or else, as in the bear, on the entire sole of the foot. In the first 

 case, the foot is generally long, and forms, with the lower end of the leg, 

 the backward directed knee. 



The feet are usually directed forwards ; only in the walrus and seal, and 

 slightly in the bat, the hind feet are directed backwards. Some are pro- 

 vided with short and broad fore feet, fitted for digging or scratching in the 

 sand. 



The normal number of toes is five, viz. the thumb, the innermost toe ; 

 next to this, the indicator-finger; then the middle finger ; next to the latter, 

 the ring-finger; and finally the outermost, the little finger. But in several 

 genera there is one finger wanting to the hind feet ; or two are wanting ; or 

 we find four toes to the fore feet, and five behind ; or four everywhere ; or 

 four to the fore, and three to the hind feet; or two before, and four behind; 

 or two before, and three behind. These toes, however, are not always 

 developed ; as, for instance, in the case of a single hoof, or of two hoofs. 

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