82 SKULL OF THE BOA CONSTRICTOR. 



firmly wedged into tlie nasal interspace ; the anterior ex- 

 panded part of this small triangular bone supports two 

 teeth. Thus, the bony maxillary arch is interrupted by 

 two ligamentous intervals at the sides of the premaxillary 

 key -bone, in functional relation to the peculiar independ- 

 ent movements of the maxillary and palatine bones re- 

 quired by serpents during the act of engulfing their usually 

 large prey. Two bones extend backwards as appendages 

 to the maxillary arch : one is the " pterygoid," 24, from 

 the palatine ; the other the ectopterygoid, 25, from the 

 maxillary. The pterygoid is continued from the posterior 

 extremity of the palatine to abut against the end of the 

 tympanic pedicle ; the under part of the anterior half of 

 the pterygoid is beset with teeth. The ectopterygoid, 25, 

 overlaps the posterior end of the maxillary, and is arti- 

 culated by its posterior-obliquely cut end to the outer 

 surface of the middle expanded part of the pterygoid. 



MANDIBULAR ARCH. 



The tympanic bone, 28 (Figs. 14 and 15), is a strong 

 trihedi\il pedicle, articulated by an oblique upper surface 

 to the end of the mastoid, and expanded transversely 

 below to form the antero -posteriorly convex, transversely 

 concave, condyle for the lower jaw. This consists chiefly 

 of an articular and a dentary, with a small coronoid and 

 splenial, piece. The articular piece ends obtusely, imme- 

 diately behind the condyle ; it is a little contracted in 

 front of it, and gradually expands to its middle part, 

 sends up two short processes, then suddenly contracts 

 and terminates in a point wedged into the posterior and 

 outer notch of the dentary piece. The articular is deeply 



