Many of the African snakes climb trees, and also suspend themselves from a branch while reaching into a bird’s nest lower down for the eggs it may contain. Both Livingstone and Dr. Andrew Smith[10] make particular mention of some of the egg-eating snakes of South Africa, the latter in his general description of ophidians stating that ‘many, perhaps all snakes, devour eggs when they have an opportunity. A few feed entirely on eggs,’ notably some of the small tree snakes, to which the name Oligodon (few teeth) has been given, this family having no teeth on the palate, like all other snakes. Their food, therefore, cannot be of a nature to require a very strong grasp, though we have no authority for stating that the Oligodons feed exclusively on eggs.
There is, however, one of the family with a dentition so remarkable that it has been considered a distinct type, and Dr. Andrew Smith, who was the first to observe its habits, gave it the generic name of Anodon (toothless), the jaws being merely roughened with the rudiments of teeth. This little snake, of about two feet in length, is exclusively an egg-feeder. ‘Its business,’ says Professor Owen in his Odontography, ‘is to restrain the undue increase of small birds by devouring their eggs.’ Its remarkable organization is favourable for the passage of these thin-shelled eggs unbroken until far back in the throat or gullet, when the egg comes in contact with certain ‘gular teeth,’ which then break the shell without any loss of the contents to the feeder. These gular teeth are a curious modification of some of the spinal processes, presenting a singular anomaly in the presence of points of enamel on the extremity of some of them.
Professor Owen has very fully described this remarkable development,[11] and as his works have been the text-books of many later physiologists, his words may here be quoted, even at the risk of repetition.
‘In the rough tree snake, Deirodon scaber, with 256 vertebræ, a hypapophysis—from ὑπὸ (Latin, sub), an offshoot from beneath—projects from the 32 anterior ones, which are directed backwards in the first ten, and incline forwards in the last ten, where they are unusually long, and tipped with a layer of hard cement (dentine). These perforate the dorsal parietes of the œsophagus, and serve as teeth.
‘Those who are acquainted with the habits and food of this species have shown how admirably this apparent defect—viz. the lack of teeth—is adapted to its well-being. Now, if the teeth had existed of the ordinary form and proportions in the maxillary and palatal regions, the egg must have been broken as soon as it was seized, and much of the nutritious contents would have escaped from the lipless mouth; but owing to the almost edentulous state of the jaws, the egg glides along the expanded mouth unbroken, and not until it has reached the gullet, and the closed mouth prevents the escape of any of the nutritious matter, is it exposed to the instruments adapted to its perforation. These instruments consist of the inferior spinous processes,’ etc., already described. ‘They may be readily seen even in very small subjects, in the interior of that tube in which their points are directed backwards. The shell being sawed open longitudinally by these vertebral teeth, the egg is crushed by the contractions of the gullet, and is carried to the stomach, where the shell is no doubt soon dissolved by the acid gastric juice.’
| Portion of spine of the Deirodon, from Andrew Smith’s Zoology of South Africa. | Gular teeth penetrating into the gullet, ib. | Portion of spine from a skeleton at the museum of the R. C. S., natural size. |
The two from Smith’s Zoology must be much magnified; the third, from the skeleton, being the true size, excepting that the ribs are broken short off, some entirely so. The minute processes extend two or more inches.
As the learned professor has described the Deirodon (neck-toothed) both under the head of teeth, and also of vertebrated animals, the two accounts are blended, but given verbatim as far as possible.