19 



down the full-grown fang, whilst in the Daboia this cavity- 

 disappears very quickly, and is only marked by the darker 

 appearance of the centre of the tooth. In fact the remains 

 of the obliterated cavity are just traceable along the posterior 

 wall of the canal and only appear plainly below the termina- 

 tion of the latter. 



The structure of the poison-fang can be studied in 

 the imperfect fangs often met with in the cobra ; it 

 frequently happens that the fang is found divested of a part 

 of the outer wall of the pulp-cavity, so that the wall of the 

 poison-canal is seen nearly isolated from the outer part of 

 the fang except at the base. 



CHAPTER IV.— Internal Organs. 



The cavity, thoracic and abdominal in one, of snakes may 

 be divided into four parts, of nearly equal length. The 

 first part contains the windpipe, gullet, heart and lungs, 

 the second contains the liver, the third contains the stomach 

 with the pancreas, spleen, gall-bladder and small intestine, 

 the fourth contains the large intestine and the urino- 

 frenital organs. See Plate V. 



In front of the windpipe lies the sheath of the tongue ; 

 to the lower extremity of the sheath is attached the point 

 of the long V shaped hyoid bone ; the upper parts of this 

 slender bone being acted on by the geniohyoid muscle 

 and the sheath itself by the genioglossal muscle, the tongue 

 is jerked up and protruded. 



The windpipe has numerous incomplete cartilaginous 

 rings in its structure. The lungs consist of a lacework of 

 air-cells lining the walls of large air cavities spread out 

 along the back of the abdominal cavity from the heart to 

 the liver. Their shape and extent vary considerably; they 

 are most extensive in the sea-snakes, a kind naturally 



