AND TEETH OF THE OPISTHOQLYPUA. 297 



The hindei' tooth in my diagram of this species is represented as 

 larger than the one in front of it. My observation is gathered 

 from the dissection of several specimens. 



Methods and Material. 



Most of the snakes used for my observation were brought from 

 India by myself. Some of them were preserved specimens, well 

 (ixed and suitable for histological purposes. 



Unfortunately others which I had hoped to keep alive for 

 physiological experiments had to be killed unexpectedly, and the 

 tissues were only imperfectly fixed. 



This investigation has necessitated the preparation and exami- 

 nation of a number of serial sections of the heads of snakes, and 

 owing to the presence of the scales and hard bones forming the 

 skull, this proved to be a difficult task. After many experiments 

 the following method was successful. 



The head was separated from the body close to the angle of 

 the jaw, and placed in the fixing and decalcifying reagent aceto- 

 bichromate (Bolles Lee, pp. 49 & 50). In order to ensure 

 thorough penetration of the fluid, an incision in the scales was 

 made just behind the eye, the lens of which was also removed. 

 After a fortnight the head was taken out, and was carefully 

 cut by means of a sharp razor into two halves by a median 

 longitudinal vertical cut. Each half was again placed in fresh 

 aceto-bichromate solution with the addition of one or two drops 

 per 100 cc. of acetic acid. I found it necessary to leave it in this 

 for three to four weeks to get conaplete decalcification. Each of 

 the halves was then used for longitudinal or transverse sections. 

 It was found necessary to leave the head in the paraffin bath at a 

 low temperature for more than twelve hours. The sections were 

 cut at a thickness of 10-1 5 /x,. Several stains were tried, and 

 I found the following most useful : Ehrlich haematoxylin 

 covTnter stained with eosin or ha3malum and eosin. Each of 

 these methods gave a good differentiation between the serous 

 and the mucous secreting cells in the poison gland, the former 

 being stained pinkish, the la,tter bluish. Both these being water 

 stains, I found that the teeth and bone were often washed off 

 the slide while being taken through the alcohol. To prevent 

 this the slides were dipped in a thin solution of colloidin in 90 % 

 alcohol. In order to verify my observations with regard to the 

 duct and its connections with the fang, I made several 

 cardboard models of portions of the jaw. 



General Discussio7i on the Teeth in the Mandible and Maxilla 

 and the Mechanism of the Hinged Teeth. 



The maxilla, mandible, and pterygoid bear teeth and these occur 

 in uninterrupted series, increasing or decreasing in size from 

 in front backwards. Sometimes a diastema is left, and this is 



