OCR Text |
Show 28 DR. J. MURIE AND MR. A. D. BARTLETT [Jan. 9, 5. On the Movement of the Symphysis of the Lower Jaw in the Kangaroos. By J A M E S M U R T E , Prosector to the Society, and A. D. B A R T L E T T , Superintendent of the Society's Gardens. A short time ago, a lady, a frequent visitor at the Gardens, on conversing with the keeper of the Kangaroos, asked him if he was aware of the manner in which these animals used the teeth of the lower jaws to snip their food as a person would do in snipping grass with a pair of scissors. She mentioned that she had resided many years in Australia, and seemed quite positive as to the truth of the fact that Kangaroos used their lower incisors in the manner already spoken of. The keeper, interested in what had been told him, called the attention of Mr. Bartlett to it. Mr. Bartlett immediately examined the teeth and jaws of several skulls of Kangaroos in his possession, and, satisfied of the probable truth of the remark, took the first opportunity of observing the same in the living animals in the Society's Collection. Since then we have corroborated and added to these observations together. The following were the different species of the living animals examined for this purpose,-viz. the Red Kangaroo (Macro-pus rufus), the Black-faced Kangaroo (M. melanops), the Great Kangaroo (M. giganteus), the Yellow-footed Rock Kangaroo (Petrogale xanthopus), Bennett's Wallaby (Halmaturus bennettii), and the Derbian Wallaby (H. derbianus). In these several species we noticed the following movements:- As the animal opened its mouth and seized the grass offered it, there was a slight though distinct separation of the lower incisors, differing in each individual according to its size,-in the large Kangaroo almost as much as a quarter of an inch. The small mouthful of grass being seized, the green blades were cropped or nipped off, a portion being evidently cut through by the anterior free sharp edge of the two lower incisors as they pressed against the opposing concavity of the palate and the cutting-edge of the upper and anterior incisors; while another portion of the food passed between the two lower incisors, and seemed also to be snipped through either by the closure or approach of the trenchant internal lateral edges of these, or it might be by the jerking movement of the head, which caused the morsel to be half torn and half cut through by these incisors. At other times, when the grass was in small loose bundles of a few of the stronger fibres with their roots attached, instead of chewing the latter, the animal rather rejected them ; but in order to do so grasped the roots or dry portion of the stem, which it wished to disengage, with its fore paws, using the claws in the manner a human being would the fingers and hands to clutch and drag an object. While doing this, what stalks were between the lower incisors were severed by their internal acute borders. After the grass had thus been cut through, it was passed between |