April 1, 1898.] 



KNOWLEDGE. 



93 



wounding the lower jaw. Of course, when the snake is 

 about to strike, the fang has to be raised again ; and with 

 this object certain modifications have been made in the 

 bones of the palate, and certain muscles have been requi- 

 sitioned to govern the necessary motions, to explain which 

 in detail would require another article as long as this one. 

 By means of this complicated machinery the fang of the 

 cobra (Fig. 5) can be erected and depressed to a limited 

 degree, though not to anything like the same extent as in 

 the case of the vipers. In the mamba, however, the diffi- 

 culty has been overcome in another way : the maxillary 

 bone is lifted in front and curved backwards (it is shaped 

 something like a sickle with about six inches of the point 

 broken off, held edge downwards i, so that the base of the 

 fang is considerably above the roof of the mouth (Fig. 6). 

 Now, these long, sharp, delicate weapons are extremely 

 likely to be broken off, and it is very necessary that there 

 should be a reserve of fangs to take their place in case of 

 accidents. Consequently, behind the functional fangs are 

 others in every stage of development : the minute germ, 

 the more markedly grooved tooth, and so on to the per- 

 fectly developed functional fang, with the edges of the 

 groove nearly joining in front (Fig. 7). This being so, the 

 necessity for taking any 

 particular care of the 

 front fangs of course 

 ceases to exist ; indeed, 

 it appears that they are 

 not unfrequently shed 

 voluntarily. 



While the sea-snakes 

 and elapines were thus 

 being armed, the back- 

 fanged snakes (ophisto- 

 glyphs) were slowly 

 becoming front - fanged 

 snakes (proteroglyphs ) also. As regards the poison-gland 

 (with the exception of the exaggerated development of 

 the Dvliiipliis), the duct, and the fang-sheath, the same 

 principles are in evidence ; but the maxillary bone has 

 been modified and turned up in front, the solid teeth 

 in front of the grooved fangs have been discarded 

 (Fig. 8), and the fangs themselves have come into position 

 in the front of the mouth— or, rather, to be more accurate, 

 the front of the mouth has come back to the faugs. 

 At the same time the edges of the groove have gradually 

 closed up, until at length they are fused, and have the 

 appearance of being tubular (Fig. 9) — an appearance 

 which has deceived many into the belief that the fang is 

 actually hollow or perforated. If the fang be bisected, 

 however, the error at once becomes evident, for the section 

 will show the semicircle of pulp completely surrounded by 

 dentine (Fig. 10). Thus came the vipers. It is true that 

 for many years it was considered that the fang machinery 

 of the viper was merely a specialization of the elapine, 

 and it is to Mr. Boulenger's researches that we owe the 

 true solution of the question. In the less specialized 

 forms of viper, such as the Cape viper (Caiisits rhombeatux), 

 "the fangs," to quote his words, " are situated on the 

 posterior extremity of the maxillary, close to its articula- 

 tion with the ecto-pterygoid — a condition which is identical 

 with that of the ophistoglyphous colubrids." In the more 

 highly specialized vipers, such as the crotalines and the 

 atractaspis, the maxillary bone has fallen away altogether 

 in front of the fangs. It is hardly necessary to say that 

 in this family the soUd teeth which were originally in 

 front of the back fangs have altogether disappeared. 



Having, as I have said, the fangs already grooved and 

 elongated before their position was altered from the back 



Fio. 8. — Portion of skull of viper 

 (rattlesnake), showing the vertical 

 position of the maxillary. 



I 



Pia. 9.— Fang (much 

 enlarged) of viper ; a, 

 ori6ce by which venom 

 enters fang ; b, orifice 

 through which venom is 

 injected into wound 

 (much enlarged). 



to the front of the mouth, it became doubly necessary 

 for the vipers to have the maxillary bone movable. 

 There was not much difficulty in 

 ,-■''" this, as that bone had already so 

 changed as to lie almost vertically 

 to the jaw instead of parallel with 

 it (Fig. 8), there being only just 

 sufficient space left on its tooth- 

 bearing face to admit of a single pair 

 of fangs. It was a comparatively 

 easy process, then, that this face 

 should become normally directed 

 towards the throat, with the fangs 

 shut back, as it were, like the blade 

 of a clasp knife, on the roof of the 

 mouth ; and that by a modification 

 of the structure of some of the bones 

 in the front of the skull, and by an 

 exaggeration of the action of the 

 motor machinery already referred to, 

 it should be possible for the snake to 

 erect its fangs vertically to the upper 

 jawwhen it was striking. It is almost 

 superfluous to say that the fangs, 

 having in their new recumbent posi- 

 tion much more room to grow in than when they were at the 

 back of the mouth, have availed themselves of the space at 

 their disposal to the fullest extent, some of them reaching 

 almost to the back of the palate. It is natural, then, that 

 the mobile erectile fangs of the viper should be longer than 

 the practically immovable fangs of the elapine. I trust 

 that no one will be misled by this sentence into the erro- 

 neous idea that the fang itself is movable : the fang ia 

 always and quite immovable ; it is the maxillary bone, to 

 which the fang is attached, that moves. 

 The viper of vipers, the most highly 

 specialized of the group, is the 

 atractaspis from Tropical Africa. The 

 solid teeth on the lower jaw and palate 

 have almost altogether disappeared — 

 there are only about eight or ten all 

 told — and the poison - fangs are so 

 enormously developed that Mr. Wood, 

 in his popular but not over reliable 

 natural history, suggests that the 

 atractaspis cannot open its mouth sufficiently wide to 

 erect its faugs, and that the poison is injected while the prey 

 is being swallowed. If this view were correct, it would be a 

 case in which ultra-development had defeated its own end, 

 for the serpent would find itself in the same position as 

 regards injecting its poison as when it was in its back- 

 fanged position — or, rather, in a worse one, for it would 

 have no solid teeth to secure its prey with. But of course 

 Mr. Wood's supposition is incorrect. The gape of the 

 viper is enormous ; it can easily open its jaws to an angle 

 of one hundred and eighty degrees ; so that it ia quite 

 clear that, however long the fangs may be, there is plenty 

 of space in which to erect them — unless, indeed, they were 

 to grow right down the throat. 



Specimens of these different families are usually to be 

 found in the reptile house at the Zoological Gardens, except 

 the sea-snakes, which die almost at once in captivity, how- 

 ever large the tank. The ophistoglyphs are usually repre- 

 sented by the Cape bucephalus ( Dispholidus tiipus) and 

 some species of sand-snake t PsammopJiis J : the elapines 

 by the cobras, and what they are pleased to call death- 

 adders (as a rule the Pseudechis porphyriacus ) : and the 

 vipers by one or two pit-vipers. They have a cotton- 

 mouth ( Ancistrodon piscivorusj there now and a fer-de- 



Fio. 10. — Section 

 of fang of viper; a, 

 dentine ; b, pulp 

 (much enlarged). 



