76 INTRODUCTION 



with large external orifice, and an inner, rather more 

 posterior in position and occupying an excavation on 

 the outer face of the maxillary bone. The inner 

 walls of these chambers are very thin and membra- 

 nous, and form a partition separating the two, except 

 for the presence of a minute opening ; this partition is 

 stretched across the hollow of the maxillary bone like 

 the membrane of a drum, and is supplied with blood- 

 vessels and nerves, the latter terminating in cells of 

 variable form. The use of the organ, thus situated 

 at the base of the poison fang, and therefore in close 

 proximity to the sphincter of the poison duct, is still 

 unknown. 



Several of the Boidae, such as Python and Cor alius, 

 have deep pits in some of the upper and lower labial 

 shields, or also on each side of the rostral shield ; 

 these problematic organs are in all probability also 

 sensory. 



