REPTILES 199 



just outside the ulnare, and the presence of an extra phalanx in 

 the third digit, and two extra phalanges in the fourth digit. The 

 extra carpal bone is known as a pisiform, and is of different nature 

 from the rest, for it has been developed in the course of a tendon 

 (see p. 48), the muscle belonging to which acquires thereby a 

 greater leverage. 



Hind-Limb Hip-Girdle. Except in unimportant particulars 

 we get a very close agreement with the theoretical type, all three 

 elements ilium, pubis, and ischium being present. Free Limb. 

 There is considerable departure from the simple type as regards 

 the tarsus, the proximal part of which is represented by one 

 element, probably representing tibiale, intermedium, fibulare, and 

 centrale, all fused together. Only two distal elements can be seen 

 in the tarsus; one of these is probably tarsale 3, for the third digit 

 is united with it, while, since digits 4 and 5 both unite with the 

 other distal elements, it perhaps may be regarded as equivalent 

 to the two corresponding tarsalia fused together. It is not clear 

 what has become of the first and second tarsalia. The digits are 

 supported by the same number of phalanges as in the hand. One 

 point is specially worthy of remark, i.e. the ankle-joint comes in 

 the middle of the tarsus, not, as in Mammals, between the tarsus 

 and bones of the lower leg. Such a mesotarsal ankle-joint is 

 characteristic of both Reptiles and Birds (see p. 146). 



Digestive Organs (fig. 131). Lizards feed on insects, small 

 worms, and the like, and possess numerous small conical teeth, 

 and a very mobile forked tongue. The teeth are not lodged in 

 sockets as in a Mammal, but are fixed on to the inner sides of 

 the bones which form the margin of the upper and lower jaws. 

 There are also two small groups of teeth on the palate. It is 

 particularly worthy of notice that reptilian teeth, as compared with 

 those of ordinary Mammals, are not only extremely numerous, but 

 not divided into different kinds incisors, canines, &c. And while 

 a Mammal develops two sets of teeth, a Reptile has, as a rule, an 

 indefinite succession of them, a worn-out tooth being replaced by 

 a new one, which grows up at its base. The tongue can be 

 protruded to some distance, and is worked by a well-developed 

 set of muscles attached to the hyoid apparatus, the large size of 

 which is thus accounted for. 



The digestive tube or gut into which the mouth-cavity is con- 

 tinued consists of a gullet, wide slightly curved stomach, fairly long 



