EXTERNAL CHARACTERS. 7 



flexible neck, the folds of skin about the shoulders, 

 and, after the tenaculum is removed, the way the head 

 is withdrawn between these folds, so that only the tip 

 of the snout is visible. So soon as the animal is dead 

 and flaccid, you can readily stretch out the neck and 

 proceed with your examination. 



3, External Characters of Head and Neck. 



a. Observe the form of the head : flattened from 

 above down ; wide posteriorly, where it is very 

 distinctly differentiated from the neck ; and 

 narrowing toward the snout. 



b. On the ventral aspect of the head and neck 

 the hyoidean apparatus can be felt through the 

 skin of the throat ; and farther back the wind- 

 pipe. 



c. The very large mouth openings provided with 

 notched horny plates instead of teeth along 

 the margins of the jaws ; note the marked 

 projection on each side of the median notch 

 of the upper jaw. 



d. On the extremity of the snout the openings 

 of the anterior nares ; a pair of round apertures 

 placed close together. 



e. The eyes, around which can be felt the ante- 

 rior margins of the bony orbits; the thick, 

 opaque upper eyelid^ and the larger, more mov- 

 able lower one ; the nictitatijig membrane^ or 

 third eyelid, may be found covering the eye- 

 ball or withdrawn to the anterior corner of the 

 eye opening ; in the latter case seize its mar- 

 gin with forceps and draw it back over the 

 eye so as to see it well ; it is much more 



