OF THE VENOM OF THE RATTLESNAKE. 15 



elongated fusiform cells, Fig. 9, each having a single nucleus, and sometimes a long, 

 dark nucleolus. 



These elements are undoubtedly the characteristic cells of non-striated muscular 

 ti.ssue.' Their presence, together with the form and position of this enlargement, 

 enables us to view it as a sphincter placed upon the duct, for the purpose of 

 restraining the wasteful flow of the secretion. This portion of the wall of the duct 

 contains numerous irregular, stellate, pigment-cells. Fig. 8, h. So far as I am 

 aware, no author has described this adjunct to the venom apparatus. Of its pur- 

 pose, however, I have no doubt ; and that some such provision does exist, is plain, 

 from the fact that, when in the living Rattlesnake the jaws are separated, and the 

 fangs caught on the edge of a thin cup, and erected, it is usually very difficult to 

 produce a flow of venom. Even when the operator presses upon the glands, the 

 poison is rarely ejected, without the voluntary aid of the snake itself^ After death, 

 the remnant of fluid in the gland, although small in amount, is easily forced out 

 along the duct, and through the fang. It is, therefore, very plain, that the snake 

 has the power to restrain the flow of venom, even when the fangs are in such a 

 position as that without the aid of the arrangement we have described, they must 

 inevitably permit of the escape of the poison. 



Beyond the sphincter, the duct becomes smaller in calibre, and the walls thin- 

 ner. To reach the fissure at the base and anterior aspect of the fang-tooth, the 

 duct runs up the posterior edge of the fossette, and winds over the rounded antero- 

 lateral shoulder of the superior maxillary bone to reach its anterior face, where it 

 communicates with the fissure in the fang. The value of the course thus taken by 

 the duct, we shall elsewhere consider. 



Another peculiarity in the course of the duct, should, however, claim attention, 

 as it has also a mechanical use. Just below the eye, the duct is abruptly bent, 

 as indicated in Fig. 5. 



In its passage from the gl'and to the tooth, the duct is held in place by a sheet of 

 rather close areolar tissue, which admits of the curves in the tube being straight- 

 ened, as occasion requires. The part nearest to the gland also receives some of the 

 fibres from the dense fascia which invests the external pterygoid muscle. 



The structure of the fang in venomous serpents has been so minutely described 

 by Owen,' that a brief synopsis of his views will be all that we shall require. I 

 have carefully examined the fang-tooth by the aid of fine sections, and I have 

 nothing to add to the following excellent description by the author above mentioned. 

 " To give an idea of the structure of this tooth, we may suppose a simple, 

 slender tooth, like that of a boa-constrictor, to be flattened, and its edges then bent 

 towards each other, and soldered together, so as to form a tube, open at both ends, 

 and inclosing the end of the poison duct. The duct which conveys the poison. 



' Dr. Woodward, who was so kind as to examine these structures, agreed with me as to their nature. 



" This is only true of the active animal ; when insensible from chloroform, the glands are easily emp- 

 tied by pressure. 



' Owen on the Skeleton and Teeth, Philada. 1854, p. 257, and Cyclopedia of Anatomy and Physio- 

 logy, article Teeth. 



