November 2, 1891. J 



KNOWLEDGE 



207 



tion between a Crocodile and a lizard. A still more impor- 

 tant difference occurs, however, in the under part of the 

 skull. Thus, whereas in a lizard the external nostrils 

 open directly through the palate into the front part 

 of the mouth, m a Crocodile the bones of the palate 

 develop a kind of flooring beneath its roof, and thus form 

 a closed passage by wliich the internal or posterior nostrils 

 are brought to the very hinder extremity of the skull. 

 This remarkable peculiarity is well exhibited m Fig. 2, A, 



Fig. 2. — Lower view (A) of skull without the lower 

 jiiw, and (B) upper view of skull with lower jaw of 

 a Crocodile. 0, orbit ; T, temporal pit ; P, palatal 

 vacuitv ; iV, internal nostrils. 



where A' indicates the internal nostrils. The small round 

 aperture seen in the front of the palate in both A and B 

 is closed during life with membrane, and thus prevents 

 any communication between the external nostrils and the 

 front of the mouth. The object of this peculiar arrange- 

 ment is to enable the animal to breathe when its mouth 

 is open under water, and the nostrils are alone in the air ; 

 this being* effected by the closing of the back of the mouth, 

 in front of the internal nostrils, by means of a fold of skin, 

 thus leaving a free communication between the nostrils 

 and the wind-pipe. The advantage of this arrangement 

 to animals which, like Crocodiles and Alligators, kill their 

 prey by holding them under water, is self-apparent. 



If to these differences between the skulls and teeth of 

 Crocodiles and lizards, we add that, whereas in. the latter 

 the ribs articulate to the joints of the back-bone or 

 vertebrae by means of little knobs on the sides of the 

 vertebrie themselves, in Crocodiles they join the summits 

 of long horizontal processes of bone projecting from the 

 upper part of these vertebrre, we think we shall have 

 said enough to convince our readers that it is altogether 

 incorrect to speak of ('rocodiles and Alligators as lizards. 

 Crocodiles are, indeed, first cousins of those extinct reptiles 

 which were described in a previous article in KNowLEnoK 

 as " Giant Land Reptiles," and they ought, therefore, to 

 be regarded with respect as being the sole existing, 

 although collateral, representatives of that great group of 

 reptiles which dominated the earth at a time when 

 mammals were only just beginning their career. 



Having said thus much as to the distinctness of Croco- 

 diles from lizards, we may proceed to consider how the 

 former differ from Alligators, and to make some mention 

 of a few of the various species of each. Now if we exiiminc 

 the skulls of the ditferent kinds of Crocodiles we shall iiiid 

 that the number of teeth in the upper jaw varies from 17 

 to 19, while in the lower jaw there are invariably 15 ; and 



we shall likewise find that the teeth of the two jaws inter- 

 lock with one another when the mouth is closed. 

 Moreover, when the jaws are in opposition it will be 

 observed that the first tooth on each side of the lower jaw 

 is received into a pit in the palate of the skull, while the 

 fourth lower tooth, which (like the first) is larger than the- 

 others, bites into a notch in the side of the skull (as 

 shown in Fig. 1), and is thus more or less distinctly visible 

 externally in the living animal. Crocodiles are now found 

 in the rivers of Africa, India, Burma, Australia, and 

 America, as well as in many of the larger islands in warm 

 regions. They vary greatly in regard to the relative 

 length of the skull, the longest-snouted species occurring 

 in South America and West Africa, while those of India 

 have the shortest and broadest skulls (Fig. 2). On the 

 other hand, if we examine the skull of an Alligator, we 

 shall find that the upper teeth bite on the outer side 

 of the lower ones without any sort of interlocking, and 

 both the first and the fourth lower teeth are receiveil into 

 pits in the skull, so that when the mouth is closed both of 

 them are totally invisible from the outer side. Moreover, 

 in no Alligator does the number of lower teeth ever fall 

 short of 17. Again, in all Alligators the skull is even 

 broader and shorter than in the Indian Crocodiles. Till 

 within the last few years it was believed (in spite of 

 the persistent assertion of sportsmen, that the Indian 

 " Magars," as they are called by the natives, are Alli- 

 gators) that Alligators were confined to the New World, 

 but recently it has been found that there is one species in 

 China. This is, indeed, a very curious instance of what 

 is known as discontinuous distribution, and one which 

 only finds a complete parallel in the case of the tapirs, of 

 which there is one species inhabiting the Malay peninsula 

 and adjacent islands, while all the others are restricted to 

 South America. There are several species of -Alligators, 

 which are divided into two groups, according as to whether 

 an armour of bony plates, or scutes, is or is not developed 

 on the under surface of the body. In the true Alligators, 

 which agree with all living Crocodilians in having a dorsal 

 armour of these bony scutes, the namber of upper teeth 

 varies from 17 to 20, and that of the lower from 18 to 20, 

 while there is no bony armour on the imder surface of the 

 body. The two well-known species are the Mississippi and 

 the Chinese Alligator,, in addition to which there is a third 

 American form of which the exact habitat is unknown. The 

 second group of Alligators, or Caimans, as they are called 

 in Brazil, is confined to South America, where it is 

 represented by five species. These are characterized by 

 having fi-om 18 to 20 upper, and from 17 to 22 lower teeth 

 on each side, and also by having the lower surface of the 

 body protected by a shield of bony scutes, which overlap 

 one another like the tiles on a roof, and each of which is 

 composed of two separate pieces united together by what 

 is known as a sutural union. 



The above, then, are the chief difterences which distin- 

 guish Alligators and Caimans from Crocodiles, and they 

 are such as surely do not justify the statement that 

 naturalists merely pretend to distinguish between the 

 two. Alligators and Crocodiles do not, however, exhaust 

 the list of living Crocodilians, since we have two peculiar 

 species diftering from all the others by the great length of 

 their snouts, and respectively inhabiting the Gauges and 

 the rivers of Borneo — the former being known as the 

 Gharial, and the latter as Schlegel's Gharial. In both of 

 these reptiles the numerous teeth are long and slender, 

 and dilYer from one another but little in size in ditferent 

 parts of the jaw, while neither of them have an armour on 

 the lower surface of the body. They dift'er from Crocodiles 

 and Alligators in feeding chiefiy on fish. 



