OCR Text |
Show 1890.] HELODERMA SUSPECTUM. 223 the vagus and condylar foramina are to be found at their mosf common sites as seen in ordinary Lizards. The anterior margin of the prootic is also notched for the passage of the 5th and 7th nerves, this notch being converted into a foramen by the membrane that helps to enclose the fore part of the cranial casket when the skull is normally complete. The 8th nerve emerges from the internal auditory meatus. Next turning to the mandible I would add a few words to what I have already said in reference to the teeth. The ducts which lead from the poison-gland upon either side do not pass directly through the ramus of the jaw to the base of the groove of the tooth to be supplied, as one might naturally suppose. Rather this is the arrangement. Let us choose a large tooth from the middle of the • series for an example. In the first place it must be noted that when the grooves upon the tooth are followed down to the base of the tooth it is not at that point that we find the internal foramen that is intended to transmit the poisonous fluid to the groove in question. The external duct enters by means of a foramen directly through the outer bony wall of the ramus. This leads into quite a cavity which exists in the body of the jaw and at the base of the tooth. Now the foramen that leads into the mouth and finally supplies the tooth with the venom makes its entrance, as I have already said, at the base of the structure, but by this I by no means intend to imply that the dental groove leads into this opening. On the other hand it is found exactly opposite the tooth and well towards the mesial plane. It will be seen that the base of the tooth slopes inwards and slightly backwards, and the reverse of this course indicates the direction of the internal division of the fora-minal passage when followed from within outwards. From the structure of these parts, then, I am compelled to infer that the fate of the venom upon being jetted from the gland is this :-it passes directly, though somewhat obliquely, through the body of the mandible, and enters the mouth through the foramen at the extreme baseof the tooth towards the median plane. Theedgesof the thickened mucous membrane on either side of the row of teeth form there a longitudinal gutter as it were; this is flooded full upon the venom being thrown into the buccal cavity, it surrounding the teeth in consequence. Then, simultaneous with this, when the reptile makes its bite, the grooves upon the teeth simply serve as conduits to conduct the venom into the wound. And when one comes to think of it, this is a very simple arrangement, the more especially so when compared with the more highly perfected poison-fangs of such a reptile as Crotalus. Heloderma has a mandible to its skull that seems to be composed of the usual number of bones found in the make-up of lower jaws of all ordinary Lizards. There is a strong well-developed articular, with its large angular process directed posteriorly, and with its articulation for the quadrate, the latter showing two concavities facing upwards, backwards, and inwards. Upon the inner side of the ramus, between the articular and the coronary, there is to be 16* |