SCIENCE-GOSSIP. 



22- 



SERPENTS' FANGS. 

 Bv Harold S. Ferguson, F.L.S. 



'THE general practice of dividing snakes into two 

 divisions of poisonous and non-poisonous has 

 been declared in the light of modern knowledge to 

 be unscientific. It is well known that all poisonous 

 snakes have poison-fangs which are grooved, and 

 that down this groove is poured the poison into the 

 wound made by the fangs ; but it has been found 

 that certain so-called harmless snakes are also 

 possessed of grooved fangs. These fangs, unlike 

 those of the very poisonous snakes, are situated 

 further back in the jaw, hence the family of the 

 Colubridae to which they, equally with the poison- 

 ous sea-snakes, and the cobras, and bungari of the 

 Elapinas belong, has been divided into three 

 divisions : the Aglypha — that is those not having 

 grooved teeth — from two Greek words meaning 

 "not" and "hollow"; the Opisthoglypha — those 

 having grooved teeth situated in the back of the 

 jaw ; and the Proteroglypha, or those with grooved 

 teeth in the front of the jaw. To the second division 

 belong many of the tree-snakes, and Mr. Boulenger 

 writes ; " Experiments recently made on Ccelopeltis, 

 a genus allied to Psammophis and Dryophis, have 

 shown that these snakes are poisonous and that 

 they paralyze their small prey before deglutition. 

 It is probable that all snakes with grooved teeth 

 will prove to be poisonous to a greater or less 

 degree, as it is clear a priori that these grooved 

 fangs are not without a function." 



Another genus of tree-snakes, Dipsas, lends itself 

 to this view, for the species comprising it have a 

 repulsive look, and with their flat heads and 

 grooved teeth might easily be mistaken for the 

 deadly poisonous snakes. I have, however, never 

 seen them exhibit any signs of having injected 

 poison into their prey. The common green tree- 

 snake of India is another possessing grooved teeth, 

 but it is a very gentle snake, and the only one that 

 the natives appear not to be in dread of, for they 

 will handle it freely, though they take good care to 

 tie up its head with a rag first. No other kind of 

 snake will they on any account touch. The grooved 

 teeth in this instance are quite at the back of the 

 jaw. It is certain that the grooves must have been 

 developed for some purpose, and it is therefore 

 reasonable to conclude that they serve as poison 

 ducts ; but as far as one can judge from seeing these 

 snakes feed in captivity, they simply seize their 

 prey and swallow it at once without letting it go. 

 There is no appearance of the prey, usually a frog, 

 being paralysed by poison, and the whole act is 

 performed so rapidly that there does not seem to 

 be time for anything of the sort to occur ; however, 

 there are the teeth 



November, 1895. — No. 21, Vol. II. 



There are then several degrees of perfection as 

 regards poison-fangs represented in the teeth of 

 snakes. First we have the grooved, fang-like teeth 

 of the tree-snakes, whose salivary gland gives a 

 secretion the properties of which can hardly be 

 said to be poisonous at all, or, at least, only in 

 a very slight degree, the fang-like teeth being 

 situated behind on a lengthened maxillary bone. 

 Then there are the deadly Elapinae, whose poison- 

 fangs are situated in front and the poison-glands 

 of which secrete an active poison ; here the fangs 

 are more deeply grooved or folded over to form a 

 channel ; they are placed on the front of the 

 maxillary, which has a slight power of movement ; 

 and lastly we have the highly developed poison 

 apparatus of the vipers, where the grooving has 

 been carried on so far that the two sides of the 

 groove have coalesced and formed a complete 

 channel, giving the appearance of a perforated 

 tooth. In these snakes the maxillaries have a 

 considerable power of movement, so that the fangs 

 can be erected or depressed at the will of the snake. 



To render these stages clear it is necessary to 

 enter a little more into detail about the bones of 

 the head of a snake. If the head of an ordinary 

 harmless snake be examined, a bone will be found 

 running from the point of the jaw as far back as 

 the eye-socket, of which it forms the base : this 

 bone is called the maxillary. In it are fixed a 

 considerable mumber of teeth. It is joined to 

 another series of bones, also studded with teeth, 

 forming an interior row; the bone joining it is 

 called the transpalatine, or transverse bone, and 

 the bones holding this interior row of teeth are 

 called the palatine and the pterygoid respectively. 

 The latter extends backwards and meets a small 

 bone called the quadrate, which unites it to the 

 skull. This is the ordinary arrangement of the 

 bones in the head of the common harmless snakes. 

 Now compare the jaws of a cobra. Here the 

 same three bones may be seen, the maxillary, the 

 transverse and the pterygoid, but their relative 

 proportions are considerably altered. The maxillary 

 is much shortened and bears the grooved poison- 

 fang, with only two or three solid teeth behind it ; 

 the transverse bone is lengthened, and as the 

 maxilla and quadrate bones are movable on the 

 skull, there is a power of movement of the fang 

 through an angle of about forty-five degrees, so that 

 in these snakes the fang is partially erectile. The 

 perfection of mechanism, however, is reached 

 in the vipers, especially in the Russell's viper 

 of India. Here the maxillary is shortened 

 excessively, and heightened so that it is higher 



K 



