58 G. S. WEST. 



in the hollow of the maxillary bone, i. e. practically in the 

 base of the poison fang, and therefore in very close proximity 

 to the sphincter of the poison duct, can these features be in 

 any way associated ? 



A careful study of the habits of these animals in their 

 native localities, especially with regard to any peculiarities 

 which they may exhibit in their mode of life, would no doubt 

 do much to elucidate the nature of the sense-organ j and it 

 seems probable that the exact function of this tegumental 

 sense-organ of the lateral line series, so characteristic 

 of a large group of viperine snakes, will not be thoroughly 

 understood until such an investigation has been made. 



DESCRIPTION OF PLATE 4, 



Illustrating Mr. Gr. S. West's paper '' On the Sensory Pit 

 of the Crotalinse." 



Reference Letters. 



b. V. Blood-vessels, c. Cuticle, c. t.f. fibrous connective tissue (together 

 with a few fine nerve-fibres), gr. Groove passing from the pit to the eye. 

 h.gl. Harderian gland, i. c. Inner chamber of pit. mx. Maxillary bone. 

 n. Nostril, n.f. Nerve-fibres, n. t. Nerve terminations, o. c. Outer 

 chamber of pit. o. ext. External opening of sensory pit. o. i. Opening of 

 inner chamber to the exterior. /). A. Poison duct. ftg. Pigmeut cells, p. m. 

 Pit-membrane. F. m. Maxillary branch of V nerve. V. o. Ophthalmic 

 branch of V nerve. 



PLATE 4. 



Fig. 1. — Laches is mutus : head viewed from the left side, showing the 

 relative positions of the sensory pit and the nostril. Nat. size. 



Fig. 2. — Lachesis mutus: anterior portion of left side of head. Nat. 

 size. The flap of tissue partly covering the external opening of the pit is 

 lifted up, showing the groove between the pit and the eye, and the external 

 opening of the inner chamber {p. i.). 



