1866.] ON THE LOWER JAW OF THE KANGAROOS. 29 



the molars, partly by the aid of the tongue and partly by the move- 

 ment of the jaws, and then, with the ordinary side to side and semi- 

 rotatory movement, the process of mastication was completed by the 

 molars. 



In watching the animals, it was at first difficult to notice the action 

 of the jaws and lower incisors which we have spoken of; and this was 

 to be accounted for by the great rapidity of the movement, which 

 was also sometimes hidden by the retraction of the lips. The open- 

 ing movement of the lower incisors seemed chiefly to occur when the 

 animal raised its head to seize the food ; for while in the act of chew- 

 ing with the molars, the incisors were either closed or hidden by the 

 lips. 



With reference to the movement of the head in animals which 

 graze or browse, as for instance in the sheep, the direction of motion 

 while in the act of cropping the grass is nearly always upward and 

 forward, though every now and again the reverse is the case. In the 

 Kangaroos, however, we did not observe this latter motion, the jerk- 

 ing movement being invariably in a forward direction. This would 

 seem to agree with and favour the act of the grass slipping between 

 the open incisors ; and as these are closed the short quick movement 

 of the head would likewise tend to cut asunder the stalk or blade of 

 the leaf. Besides the direct forward jerk, the head at the same time 

 moved slightly laterally, though this was not so very perceptible. 



From these observations, then, we are inclined to believe that the 

 lower incisor teeth in the Kangaroos act in the manner either of a 

 pair of cutting-forceps or short-bladed scissors (see fig. 2), with also 

 occasionally a knife-like action ; that is to say, the lower incisors 

 themselves, if to a certain extent fixed, would on their closure pre- 

 vent the blade of grass from slipping (from, in many cases, their 

 points being perfectly close and their bases more open), and the 

 jerk combined with the dragging movement would cut it through. 



Upon consulting the various authorities as to what has been said 

 respecting the movement of the teeth and lower jaws of the family 

 of Kangaroos, we find Mr. Waterhouse states, in his admirable work 

 the 'Natural History of the Mammalia,' vol. i. p. 51, of the Macro- 

 podides, that " the lower incisors are horizontal, long, compressed, 

 and lanceolate, and have cutting external and internal margins ; 

 their outer surface is convex, and the inner surface is strongly 

 convex in the transverse direction, in the middle, but concave near 

 the margins ; when the mouth is closed, the outer cutting-edge of 

 the lower incisors is brought in contact with the cutting-edges of the 

 posterior incisors of the upper jaw on either side, and their points 

 shut within the apex of the foremost pair of the upper jaw. In 

 Macropus major (and perhaps in some nearly allied species) the 

 rami of the lower jaw are loosely attached at the chin, and at the 

 apex they are free, and the animal has the power of slightly sepa- 

 rating the lower incisors, so that their outer cutting-edges are brought 

 more closely in contact with the upper incisors than they otherwise 

 would be." 



Although Mr. Waterhouse therefore has pointed out both the 



