SKULL OF THE BOA CONSTRICTOR. 83 



grooved above, and produced into a ridge below. The 

 coronoid is a short compressed plate ; the splenial is a 

 longer, slender plate, applied to the inner side of the 

 articular and dentarj, and closing the groove on the 

 inner side of the latter. The outer side of the dentary 

 offers a single perforation near its anterior end, which is 

 united to that of the opposite ramus by elastic ligament. 



By the above-described mode of union of the extremi- 

 ties of the maxillary and mandibular bones, those on the 

 right side can be drawn apart from those on the left, and 

 the mouth can be opened not only vertically, as in other 

 vertebrate animals, but also transversely, as in insects. 

 Viewing the bones of the mouth that support teeth in 

 the great constricting serpents, they offer the appearance 

 of six jaws — four above and two below; the inner pair 

 of jaws above are formed by the palatine and pterygoid 

 bones, the outer pair by the maxillaries, the under pair 

 by the mandibles, or " rami," as they are termed, of the 

 lower jaw. 



Each of these six jaws, moreover, besides the move- 

 ments vertically and laterally, can be protruded and re- 

 tracted, independently of the other : by these movements 

 the boa is enabled to retain and slowly engulf its prey, 

 which may be much larger than its own body. At the 

 first seizure, the head of the prey is held firmly by the 

 long and sharp recurved teeth of all the jaws, whilst the 

 body is crushed by the overlapping coils of the serpent ; 

 the death-struggles having ceased, the constrictor slowly 

 u.ncoils, and the head of the prey is bedewed with an 

 abundant slimy mucus : one jaw is then unfixed, and its 

 teeth withdrawn by being pushed forward, when they 

 are again infixed, further back upon the prey ; the next 

 jaw is then unfixed, protruded, and reattached ; and so 



