ON THE SKNSORY PIT OF THE GROTALIN^. 59 



Fig. 3. — Lacliesis niutus: enlarged surface view of the pit-membrane, 

 showing tiie characteristic folds. 



Fig. 4. — Cro talus terrificus: iiead of adult from left side. Nat. size. 



Fig. 5.— Crotalus scutulatus: head of embryo from left side. Nat. 

 size. (At this stage the scales are well marked.) 



Fig. 6. — Lachesis Wagleri: anterior portion of head from left side. 

 X 2. The posterior edge of the lower antorbital scale is slightly reflected to 

 show the external opening of the inner chamber {o.i.). 



Figs. 7 — 9. — Crotalus triseriatus : nerve terminations from a teased- 

 up pit-membrane. X 520. 



Fig. 10. — Crotalus terrificus : portion of a section to show the tissues 

 between the inner chamber and the maxillary bone, x 520. 



Fig. 11. — Lachesis gramineus: surface view of the crenulated cuticle 

 covering the inner wall of the inner chamber, x 500. 



Fig. 12. — Lachesis lanceolatus: anterior portion of head from right 

 side. X 2. 



Fig. 13. — Lachesis mutus: dissection of left side of head from above 

 to show the nerve supply of the sensory pit. Nat. size. The dotted line 

 indicates the depth of the pit. 



Fig. 14. — Crotalus terrificus: vertical section through the entire 

 sensory pit of adult. X 18. Nerve-fibres from branches of the V nerve 

 are seen passing into the pit-membrane. 



Fig. 15. — Crotalus terrificus: section of pit-membrane of adult animal. 

 X 520. 



Fig. 16.— Crotalus scutulatus: section of pit-membrane of embryo. 

 X 520. 



Fig. 17.— Crotalus triseriatus: section of lower portion of sensory 

 pit. X 75. The larger nerve-fibres are shown out black by Weigert's 

 method. 



