ON THE SENSORY PIT OP THE CROTALIN^. 49 



On the Sensory Pit of the Crotalinse. 



By 



G. S. IVest, B.A., A.R.C.S., 



Hutchinson Student, St. John's College, Cambridge; Professor of Natural 

 History at the Royal Agricultural College, Cirencester. 



With Plate 4. 



The distinguishing character of the group of vipers known 

 as the CrotalinsB is the depression or "pit" on each side of 

 the head between the eye and the nostril. Cope ^ defines 

 the group as vipers possessing "a deep fossa on each side 

 behind the nostrils, partly occupying the excavated superior 

 maxillary bone ; " and Boulenger ^ gives the following 

 characters for the crotaline as distinguished from other 

 viperine snakes : — " A deep pit on each side of the snout, 

 between the nostril and the eye ; maxillary hollowed out 

 above." 



The earliest mention of this feature — which is mainly 

 responsible for the appearance of extreme ferocity which 

 these snakes present — was by Russell and Home/ who gave 

 a rough figure of the pit in the head of the " fer-de-lance " 

 (Lachesis lanceolatus). Leydig''^ in 1868 was the first 

 to prove that this pre-orbital pit was a sense-organ. He some- 



1 Cope, 'Proc. Acad. Philad.,' 1859, p. 334. 



- Boulenger, 'Catalogue of Snakes in Brit. Mus.,' vol. iii, 1896, p. 464. 



^ E-ussell and Home, "Obs. on the Orifices in certain Poisonous Snakes 

 between the Nostril and the Eye," 'Phil. Trans. E-oy. Soc.,' 1804. 



^ F. Leydig, " Ueber Organe eiues sechsten Sinnes." " Zugleich als 

 Bcitrag zur Kenntniss des feineren Baues der Haut bci Amphibien und 

 Reptilien." ' Novorum Actorum Academ. Csesareae Leop. Carol. Germ.,' nat. 

 cur., T. xxxiv, 1868. 



VOL. 43, PART 1. — NEW SERIES. D 



