as well as his peculiar knowledge of dental structures, entitle his views to great respect.

At my request, Dr. Johnston has repeated his observations, and most kindly placed them at my disposal. The following statement is in his own language:"The study of heads prepared by me, leads me to entertain the following opinion as to the manner in which secondary fangs establish a communication with the poison duct. There appears to me good reason to believe that there is a periodical fall of the venom fangs, quite independent of violence; and this is to be regarded as a physiological circumstance agreeing with what takes place in fishes, as Pike or Gar, and in reptiles, as Iguana, as well as with what occurs in the jaws of Megalosaurus, Hadrosaurus, etc. For I have not observed in the jaws of Crotali of the same species a constant relation between the size of the serpent and of its fangs; and when I couple with the disproportion alluded to, the fact, that at nearly all seasons, reserve fangs and germs are found in every degree of advancement or development, I cannot suppose that the almost mature secondaries are awaiting an accident to effect their promotion. We know that in Alligator especially, the secondaries occasion by their development the erosion of the base, and the consequent displacement of their predecessors, and assume positions from which they are to be in turn expelled.

"In Crotalus, the secondary fangs lie in separate capsules at the bottom of the dens in the mucous membrane, where the fangs crouch when not erected. Their pulps are arranged in order upon a gum which lies at the base and to the inner side of the functioning fang; and each developing fang is inclosed in a separate capsule and points directly backwards.

"Now a transverse section of a pulp in any part of its extent, gives a crescentic figure, hardly perceptible as a crescent at the point, evidently lunate with separate horns on either side of the distal aperture of the poison canal, and again a crescent, but with closely approximated cornua, throughout the rest of the crown, where the two longitudinal folds of dentine meet along the median line and are fused together. "As the growth of the tooth advances, a slight annular enlargement marks its neck, or at least the limit of the crown, and then the two horns of the pulp diverge widely, at the upper part of the base, which is in process of formation, but again approach each other, yet without meeting, as the base goes on to completion. It may here be remarked, that the pulp acquires greater volume at this part of the fang, which is more extended along the posterior edge than in front, and is marked, both internally and externally, with conspicuous longitudinal flutings.

"The dentine of the basal portion in front, necessarily follows the modelling pulp; and as this, by the separation of the anterior lamellæ, leaves an ovoidal hiatus, so the tooth substance investing the matrix shows the free edge of its folds on either side as the margin of a large aperture, the inlet of the poison canal. this occurs while yet the tooth-capsule is entire.

All

“In this condition the secondary fang remains until the fang in use falls spontaneously or by violence; and the secondaries behind it will be found to exhibit successive inferior stages of development. At length the prime fang is removed, if spontaneously, by the atrophy of the pulp, and, I believe, by erosion of the basal

anchylosed portion; if it be broken off by violence, the freedom of the pseudo socket is accomplished by the same means. And now the first tooth of reserve is urged forwards into a recess in the maxillary bone directly adjacent to, and on the inner side of the fallen fang; and the requisite advancement is brought about by the developmental vis à tergo of the remaining reserve pulps, and probably also by the traction in front, exerted by the cicatrizing parts. It is evident that the fang emerges from its capsule, and that the point and crown repose in the den, but the base is closely invested with the capsular remains under the form of a periosteal expansion, which is the mediate bond of union between the base and the new and shallow socket of the maxilla.

"As may be perceived, upon examination at this stage, two sockets co-exist in the same jaw. The inner, new one, supporting the recently promoted fang, and the outer, old, and now vacant one, which is fast being disencumbered of the vestiges pertaining to its former resident. In this maxilla, the new fang occupies the innermost part, having the old socket on the outer side, while in the opposite maxilla, the older venom fang may be discovered in its normal situation, leaving the recess to its inner side vacant, for the temporary lodgment of its successor. Or, both fangs being recently fixed to the jaw, the vacuities will both be formed on the outside, and all the reserve fangs will appear to follow backwards and outwards in direct line.

"Now let us look at the situation of the poison duct, and examine into the mode by which it is brought into relation with the fang.

"The venom duct arising from the gland makes a bend upwards, immediately beneath the eye, then advances forwards under the skin, as far as the crotaline fossette, and lying upon the maxilla externally, plunges downwards, and pierces the gum in front of the fang, where it terminates in a papilla, which projects slightly into the proximal aperture of the tooth. In this position, it is maintained by the gum which clasps the base laterally and in front, with considerable firmness, its inferior or distal edge, encompassing the annular enlargement already alluded to. Nor is there any other than a mediate application of the poison papilla against the fang, for as the whole venom canal of each tooth is really upon the outside of the organ, no special membrane lines it which might be continuous with the duct that discharges into the upper aperture.

"Such is the condition of things in an old fang, occupying its normal exterior position. But when the tooth drops out, or is broken, the gum is left entire; or, if its exodus has been forced, the gum escapes with laceration only. In either case, however, the gum remains as a barrier, limiting the progress of the advancing reserve fang; and while the latter is establishing itself provisionally, the gum encircles it, clasps it tenaciously, and brings the poison papilla in apposition with its dental aperture. As time passes, the new fang moves gradually outwards to its permanent seat; the inner maxillary recess is restored, and the first fang of reserve is again discovered on the inner side of its senior, resting with its pulp attachment in the bottom of the recess.

"Thus, the reserve fang has become an adult functioning fang, nor does its pulp

relax its hold, until fate or mischance dislodge the now fatally-armed tooth which it animates."

Before leaving this portion of the subject, it is proper to state that the views expressed by my friend Dr. Johnston, as to the want of direct continuity between the duct of the poison gland and the tooth canal, have been recently advocated by Prof. Jeffries Wyman, of Boston. It gives me great pleasure to point out this coincidence of opinion; and while acknowledging Prof. Wyman's priority of claim as established by publication, I must not omit to add that Dr. Johnston's manuscript notes-which I have quoted above-bear the date of Oct. 3d, 1859, since which time they have been in my own possession.1

The accompanying diagram, Fig. 10, illustrates our views as to the direction taken by the new fang, in its progress towards the alveolar socket.

It will have been observed that Dr. Johnston states, that the first reserve fang enters the semilunar socket in the maxilla, to the inside of the active fang. Although this is often or usually the case, it is not uncommon to find the two fixed

a, Alveolar socket; b, functionary fang; c, its successor; d, the next fang in order of age; e, remaining germs.

fangs, unsymmetrically placed, one on the inner, the other on the outer side, of their respective alveolæ, or both on the inner side; or again, both on the outer side of the said socket.

In all other points, my own researches agree with those of Dr. Johnston.

May 16th, 1860; Proc. Boston Nat. Hist. Soc.

CHAPTER III.

THE PHYSIOLOGICAL MECHANISM OF THE BITE OF THE CROTALUS.

THE preceding details will enable us to understand the following statement of the functions of the various parts described, and to appreciate the mode in which they combine to effect a given purpose.

Of the many authors who have treated of the anatomy and physiology of the Rattlesnake and other venomous serpents, no one has entered fully into the subject of the mechanism of the movements which inflict the bite and inject the poison. Redi, Fontana, Tyson, Ranby, Smith, Home, Duvernoy, Soubeiran, and others, have nearly all in turn contributed something to this subject, but I find nowhere a full and complete account of the part played by the various muscles and of the exact uses of many of the peculiar arrangements of tissue which characterize the poison apparatus. Nothing, in fact, can be more admirable than the mode in which the motions in question are effected, and yet while they interest the physiologist, from the wonderful example they afford of a series of complex acts following one upon another in ordered sequence, to effect a certain end, they are not less interesting to the physician, who may learn from their study how he may be deceived as to the occurrence of poisoned wounds, and how the snake which appears to strike may really fail in its object, even though seeming to have inflicted a wound.

When the Rattlesnake is in repose and unmolested, it sometimes lies at length, sometimes coiled, or wrapped fold on fold in the loops formed by other snakes which may happen to be in the same box. So soon, however, as cause is seen for alarm, the snake extricates itself, if among others, and at once throws its body into the coil so familiar to any one who has seen serpents, whether venomous or not. Sometimes on the edge, more often in the centre of the coil, the tail projects far enough to admit of its vibrating freely, and with singular swiftness.

The head is raised a little above the rest of the body, but not, usually, more than three or four inches, even in large snakes. The neck and upper end of the trunk are not thrown into complete circles, but lie in two or three abrupt curves across the mass of the coiled body. The snake is now in position to strike. While thus at bay, in an attitude of singular grace, the long black tongue is frequently protruded, a common movement among all serpents when irritated. Just before the blow the snake makes a hissing sound, which is caused by the act of expiration, and is due to the passage of air through the narrow glottis. It is louder in certain innocent serpents than in the Crotalus.

The mechanism of the forward cast of the body, which next occurs, is a very

simple matter. The muscles which lie upon the convexity of the bendings formed by the upper part of the snake, are suddenly and violently contracted, so as abruptly to straighten the body, and thrust it forward in a direct line. The force resulting from this motion is not very great, as I have often ascertained when a snake has struck the end of a pole which I was holding, nor would it alone suffice to bury the fang in a tough skin, were it not for the acts which follow and aid it. In effecting this forward thrust of the neck and head, the serpent employs only the upper part of its body, and, consequently, is unable, under any circumstances, to strike at a greater distance than one-half its length, while usually its projectile range does not exceed a third of its length. An impression prevails that when the snake lies coiled, its head is raised very high to enable it to strike downwards. It seems, however, to be of no moment, in what direction the danger threatens, since it can, at will, cast itself forwards, downwards, or almost directly upwards. As the animal comes within reach, of which the snake does not always judge with accuracy, the latter executes the movement just described. At the instant, and while in motion, the jaws are separated widely, and the head is bent somewhat back upon the first cervical bones, so as to bring the point of the fang into a favorable position to penetrate the opposing flesh. Owing to the backward curve of the tooth, this, of necessity involves the opening of the jaws to such an extent, that an observer standing above the snake, can see the white mucous membrane of the mouth, as the blow is given. The peculiar articulation of the lower jaw upon an intermediary bone, in place of upon the body of the skull, greatly facilitates this action. On examining the neck and head, it will also be seen that the head, under the influence of the cervical prolongation of the mass of the spinal muscles, is capable of being bent backwards to no inconsiderable extent. Consentaneously with the forward thrust of the body, and with the opening of the mouth, the spheno-pterygoids act from their firm cranial attachments to draw forward the pterygoid plate, and thus, through its attachment to the maxillary to erect the fang. The function of elevating the fang belongs alone to this muscle, which has no analogue in the other vertebrate animals. I have frequently tested its power to raise the fang, by stimulating it with galvanic or other irritants, after decapitating the snake, and although some French observers seem to have had doubts as to the agencies which effect the elevation and depression of the fang, there does not seem to me to be any reason to doubt the share which the spheno-pterygoid takes in this mechanism. That the mere act of opening the mouth, of necessity raises the weapon, has often been affirmed, but it is only necessary to separate the jaws of a living Crotalus to be convinced that this is not the case, and that even when the mouth is widely opened, the animal has the most perfect control over the movement of the fang, raising or depressing it at will.

As the spheno-pterygoid acts, the submaxillary bone rocks forward upon its lachrymal articulation. When the motion reaches its limit, and is checked by the ligament which I have described, the supporting lachrymal bone, in turn, yields to the power applied through the maxillary bone. These movements elevate a little the muzzle of the snake, so as to give to the face a very singular expression during the act of striking. Their more obvious and important result, is the elevation of