90 SECTION OF THE BOA CONSTRICTOR'S SKULL. 



tioQ ; there is no natural undulation of tlie body upwards 

 and downwards — it is permitted only from side to side. 

 So closely and compactly do the ten pairs of joints be- 

 tween each of the two hundred or three hundred vertebrae 

 fit together, that even in the relaxed and dead state the 

 body cannot be twisted except in a series of side coils. 

 In the construction of the skull, which has merited a de- 

 scription in some detail, and well deserves a close study, 

 the thickness and density of the cranial bones must strike 

 the mind as a special provision against fracture and injury 

 to the brain. When we contemplate the still more re- 

 markable manner in which these bones are applied, one 

 over another, the superoccipital (Fig. 17), 3, overlapping 



Fig. 17. 



V dc tn 

 SECTION OF SKULL, BOA CONSTRICTOR. 



the exoccipital, 4, and the parietal, 7, overlapping the 

 superoccipital — the natural segments or vertebrae of the 

 cranium being sheathed, one within the other, like the 

 corresponding segments in the trunk — we cannot but 

 discern a special adaptation in the structure of serpents 

 to their commonly prone position, and a provision, ex- 

 emplified in such structure, of the dangers to which they 

 would be subject from ftxlling bodies and the tread of 

 heavy beasts. Many other equally beautiful instances of 

 design might be cited from the organization of serpents, 

 in relation to "the necessities of their apodal vermiform 



