1848.] MANTELL ON ORGANIC REMAINS IN THE WEALDEN. 41 



the largest example in the British Museum. Teeth of this reptile 

 are very rarely found at Hastings. 



Upper and lower jaw of the Iguanodon. — But the specimen of the 

 highest interest that has been lately discovered is a considerable por- 

 tion of the lower jaw of an adult Iguanodon with three successional 

 teeth in place, obtained from a quarry in Tilgate Forest by Capt. 

 Lambart Brickenden, F.G.S., to whose liberality and ardent love of 

 science I am indebted for it. This fossil consists of the right den- 

 tary and opercular bones ; it is twenty-one inches long, and when 

 perfect must have been two feet in length. According to the pro- 

 portions of the maxillary elements in the Iguana, the entire length of 

 the jaw to which this specimen belonged was four feet. Two succes- 

 sional teeth, and vestiges of a third, remain in their natural situation, 

 within the internal alveolar parapet ; and there are sockets, or rather 

 excavations, for nineteen or twenty mature teeth in the outer wall of 

 the alveolar process. The implantation of the teeth was intermediate 

 between the pleurodont and thecodont types. 



As this specimen is the first unequivocal example of the lower jaw 

 of an Iguanodon hitherto known, it is of the highest interest in a 

 palseontological point of view. A fragment of the upper jaw — the 

 anterior part of the left maxillary bone — discovered by me, and now 

 in the British Museum, interpreted by the aid afforded by this recent 

 acquisition, has enabled me, with the valuable assistance of that emi- 

 nent comparative anatomist. Dr. A. G. Melville, to obtain some im- 

 portant and very unexpected results. But as I have laid before the 

 Royal Society, in whose Transactions my first memoir on the teeth of 

 the Iguanodon was published in 1825, a full accomit of the anatomical 

 characters of the maxillary and dental organs of this reptilian herbi- 

 vore, and the physiological deductions resulting therefrom, I will only 

 briefly notice a few of the most striking peculiarities. 



In the Iguanodon, the true saurian type of structure is manifested 

 in the mode of implantation and constant reproduction of the teeth, 

 and in the composite construction of the lower jaw, each ramus con- 

 sisting of six pieces. But the teeth of the upper and lower maxillae 

 are placed in a reversed position in relation to each other, as in the 

 Ruminants ; the enamelled coronal facets of the lower series facing 

 the inside of the mouth, and those of the upper the outside. From 

 the appearance of the abraded coronal portion of the used molars, 

 it is evident that the teeth of the opposite jaws were arranged sub- 

 alternately or intermediately, for the grinding surface of each tooth 

 presents two facets, from the attrition of two antagonist teeth. 



Another most extraordinary modification of structure is presented 

 by the anterior part of the dentary bone ; and it is one that could not 

 have been predicated from any thing previously known as to the max- 

 illary organization of reptiles. The symphysial portion, or front of 

 the lower jaw, instead of being crested by the alveolar process beset 

 with teeth, and continued uninterruptedly round the mouth, as in 

 existing lizards, is edentulous, and contracted in a vertical direction, 

 extending horizontally, and uniting by suture with the opposite side. 

 Thus the two rami form by their union an expanded scoop-like pro- 



