250 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



as for example the Chameleons the length of the jaw of 

 this Iguanodon must have exceeded three feet. 



The sketch of the lower jaw, represented as seen from above, 

 in Lign. 55, is intended to convey an idea of the remark- 

 able form of this part of the skeleton ; the restoration of the 

 articular part, drawn in outline, is of course ideal ; it is taken 

 from the corresponding portion of the lower jaw of the Iguana. 



PORTION OF THE UPPER JAW OF THE IGUANODON. ' Middle 

 Shelf of Wall-case C. This specimen consists of the ante- 

 rior part of the left maxillary bone, having on the under 

 surface the alveolar furrow with the bases of the sockets of 

 ten teeth; and on the upper, the deep channels of the infra- 

 orbital vessels and nerves that supplied the teeth and integu- 

 ments of the front of the jaw and face on the left side. Dr. 

 MELVILLE, 2 who kindly aided me by his profound anatomical 

 knowledge in the investigation of the maxillary organs of the 

 Iguanodon, and devoted much time and attention in insti- 

 tuting the necessary comparisons between the fossils in my 

 own cabinet and those formerly collected by me, and now in 

 the British Museum, with the jaws and teeth of recent rep- 

 tiles, favoured me with the following observations on this 

 specimen : 



" This fragment of the left maxilla, which is eight inches five lines 

 long, and two inches seven lines broad, formed the lower boundary of 

 the nasal surface ; it is broken off where the vertical parapet rises to 

 enclose the olfactory fossa. The corresponding part in the skull of an 

 Iguana (/. tuberculata), measuring four inches two lines in length, is six 

 lines long, or nearly one-eighth that of the cranium ; this ratio gives 



" Iguana which may with greater probability than the rest be supposed 

 to have the proportions of the corresponding part of the Iguanodon, it 

 is the lower jaw, by virtue of the analogy of the teeth and the sub- 

 stances they are adapted to prepare for digestion. Now the lower jaw 

 gives the length of the head of the Iguana, and this equals the length 

 of six dorsal vertebrae ; so that as five inches rather exceeds the length 

 of the largest Iguanodon vertebra yet obtained, with the intervertebral 

 space superadded, on this calculation the length of the head of the largest 

 Iguanodon must have been two feet six inches" 



1 1 discovered this fossil in 1838, in a quarry near Cuckfield. By the 

 kind permission of Mr.Kb'NiG, the specimen has recently been cleared 

 of the sandstone with which it was partially invested, so as to render 

 its characters more obvious. It is figured in " Philos. Trans.," 1848. 

 PI. XIX. 



2 JSTow Professor of Zoology in Queen's College, Gal way. 





