Systematre Course. 68 
(c) Viperide (Viperine snakes).—These are poisonous snakes, 
with triangular heads. They have the anterior maxillary 
teeth enlarged and grooved for injecting the poison 
fluid. They can be easily recognised by the peculiar broad 
triangular head, narrow neck, short tai] and the numerous 
small seales with which the whole body, and especially 
the neck and the sides of the head are covered. They 
may be classified as (1) Viperine (True Vipers), and (2) 
Crotaline (Pit Vipers). 
(1) Vipertne (True Vipers).—These vipers have no 
loreal pit between the eye and the nostril, and 
are excessively poisonous. The only species which 
the students are likely to meet with in India are 
the Daboia (Chain or Russell’s viper) and the 
Echis. The first can be recognised by its chain- 
like markings, and the second by its peculiar 
serrated scales. The students should sketch 
the head of these forms in the School Museum, 
noticing particularly the absence of the loreal pit. 
(2) Crotaling (Pit Vipers).—These vipers have a well- 
marked loreal pit, which isa little hole in the 
side of the head between the eye and the nostril. 
They comprise a number of species, which are all 
poisonous but not so deadly as the true vipers. 
The students should .sketch the side of the head 
of one of the Crotaline from the school collection, 
indicating the position of the loreal pit, which is 
the easiest feature for recognising them, 
Birps. 
Lixe the reptiles, Birds are air-breathing vertebrates in which the skull 
articulates to the vertebral column by means of a single occipital condyle. 
The mandible articulates to the skull by means ofa pair of quadrate 
bones. Birds themselves are warm-blooded; they are clothed with 
feathers, which are modifications of the epidermis, They have the fore- 
limbs converted into wings. The jaws are covered with a horny epider- 
mal sheath. The heart is divided into four chambers, and the aortic 
arch is single and curves over to the right side. The lungs are firmly 
fixed to the back of the thorax and have air-sacks in connection. For 
details of the structure of a typical bird, see the chapter on the dissection 
of the sparrow. 
Birds are chiefly of importance in Indian forests—(a) as distributors 
of the seeds of such trees as the figs, mulberry, sandal and the parasitic 
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