150 OPHIDIA. 



with the blow by which the Serpent inflicts its 

 wound, the poison is at the same moment injected 

 with force into the wound from the tip of the 

 perforated fang." 



A singular exception to the general structure 

 of the teeth occurs in a South African Snake 

 {Deirodon, Owen), described by Dr. Andrew 

 Smith, which is so interesting that we quote 

 Professor Owen's description of the dentition and 

 its use. The teeth are so small as to be scarcely 

 perceptible ; and are besides so soon liable to be 

 lost, that the reptile has been described as tooth- 

 less. The ofiice assigned to this Serpent is to 

 keep down the inordinate increase of the smaller 

 birds, by preying on their eggs ; and, as has been 

 observed, the apparent defect in its dentition is 

 in reality one of those beautiful instances of 

 adaptation of structure to the exigencies of the 

 case, to which every naturalist has so often to 

 advert. " If," says Professor Owen, " the teeth 

 had existed of the ordinary form and proportion, 

 in the maxillary and palatal regions, the egg 

 would have been broken as soon as it was seized, 

 and much of its nutritious contents would have 

 escaped from the lipless mouth of the Snake 

 in the act of deglutition ; but, owing to the almost 

 edentulous state of the jaws, the egg glides along 

 the expanded opening unbroken, and it is not 

 until it has reached the gullet, and the closed 

 mouth prevents any escape of the nutritious 

 matter, that the shell is exposed to instruments 

 adapted for its perforation. These instruments 

 consist of the inferior spinous processes of 

 the seven or eight posterior cervical vertebras, 

 the extremities of which are caj)ped by a layer 



