112 HIGH SCHOOL ZOOLOGY. 



Fiff. 82 Scales of the head in Coluber (Bascanium) constrictor. 



(After Garman.) 



1, Rostral. 2, Nasals. 3, Loreals. 4, Preoculars or Antorbitals. 5, Postoculars or 

 Postorbitals. 6, Temporals. 7, Internasals. 8, Prefontals. 9, Frontal, 10, .Supracili- 

 aries or Supraoculars. 11, Parletals. 12, Occipitals. 13, Labials. 14, Infralabials. (lie- 

 tween the iiifralal)ials are the submentals, and clothing the tip of the lower jaw the 

 mental). 18, Ventrals. 19, Dorsals. 



19. One of the chief peculiarities of the Ophidia is their 

 method of securing their prey, and bolting it undivided. Some 

 of the larger forms are dependent entiiely on the flexibility of 

 tlie vertebral column and the power of the trunk and intercostal 

 muscles for strangling their prey, but the smaller snakes either 

 seize their victims with their teeth, or first inflict a fatal wound 

 with their poison-fangs. The poisonous snakes must be re- 

 garded as the most specialized of the Oi)hidia, for the teeth are 

 not only reduced in number in comparison with the harmless 

 forms (where they may be as numerous as in the Teleosts), but 

 the poison-fangs (which are confined to the maxillaries), are 

 either provided with a groove on the anterior surface, or with a 

 canal connected with the ducc of the poison-gland, — a special- 

 ized part of the glands of the upper lip, which is compressed 

 by the muscles which close the jaws. That the snakes may be 

 enabled to swallow their booty whole, a process which is often 

 a very gradual one, the parts of the mouth are provided with 

 extraordinary mobility. The pterygo-palatine bar is capable of 

 greater movement than is even possible in tlie fishes, where it 

 will be remembered its bones are not incorporated with the 

 cranium, and not only is the quadrate bone freely moveable, 

 but the squamosal which supports it, is hinged to the skull, 



