56 STRUCTURE OF OPHIDIANS. BOAS, ^ 



of the temporal bone, called mastoid bone, (ma.) which is also 

 separate from the cranium, and attached to this bony case by 

 ligaments and muscles only ; the branches of the upper jaw are 

 not fixed to the intermaxillary bone except by ligament, which 

 permits them to separate more or less; the palatine arches also 

 participate in this mobility. Another character, peculiar to this 

 group, is the existence of sharp teeth, curved backwards, planted 

 in these arches as well as in the upper and lower jaws. 



49. In other respects the armature of the mouth varies, and 

 these differences are of great importance ; for they coincide with 

 the existence or absence of an apparatus for the secretion of an 

 active poison, which the animal 'uses to kill the prey it bites. 

 Ordinary serpents are therefore divided into venomous serpents, 

 and serpents which are not venomous. 



Fiq. 18.* 50. The NON-VENOMOUS SERPENTS, are re- 



cognised by their teeth, no one of which is 

 moveable or hollowed by a canal or gutter ; 

 they are all fixed, and they form in the mouth 

 four nearly equal ranges above, (Fig. 18.) 

 and two below. 



5J. Those serpents that have the under 

 part of the body and tail furnished with a 

 single band of transverse scales are described 

 under the name of Boas; and we give the 

 collective name of Colubers to those in which 

 the under part of the tail is covered by plates 

 im in pairs, divided on a middle line. 



52. The division of BOAS is composed of Boas properly so 

 called, of Erix, &c. 



53. The BOAS PROPERLY so CALLED, have a compressed body, 

 a prehensile tail, a hook on each side of the anus and small scales 

 on the back of the head at least. The largest serpents known, 

 belong to this genus ; certain species attain thirty and even forty 

 feet in length, and manage to swallow deer, and, as we are 

 assured, even oxen. They are unprovided with venom, but, 



* Exportation of Fig. 18. The bony head of a Non-venomous Serpent 

 seen from below : c. the cranium, im. the intermaxillary bone, m. the 

 maxillary bones, p. the palatine bones. 



49. Is the mouth, in all ordinary Serpents, armed in the same way ? How 

 are ordinary Serpents divided ? 



50. How are the Non-venomons Serpents recognised? 



51. What are Boas ? What are Colubers? 



52. How is the division of Boas divided? 



53. What are the characters of Boas properly so called ? What are their 

 habits ? To what part of the world do Boas belong ? What is the Divine Boa? 



