2yS BRITISH FOSSIL REPTILES 



more numerous than iu the younger jaw, but are arranged, as in that jaw, along the 

 outside of the alveolar wall, beginning near the base of the coronoid process, and 

 extending down the edentulous sloping part of the jaw ; their size is exaggerated in 

 the figure given in the ' Philosophical Transactions,' and there is no particular anterior 

 foramen, larger than the rest, and meriting, as in the mammalia, the name of " foramen 

 mentale." The exterior marginal groove of the edentulous border is better marked in 

 Capt. Brickenden's than in Mr. Holmes's specimen, but the alveolar wall has suffered 

 more injury in the Tilgate specimen than in that from Stammerham ; in the latter, 

 indeed, it seems to be entire, and so much of the thin inner border is preserved as to 

 show that there was not any internal alveolar wall co-extensive with the outer one. I 

 cannot discern evidence of more than 18 dental depressions on the outer alveolar wall 

 of the large lower jaw from Tilgate ; the number, therefore, is the same as in the 

 specimen from the younger Iguanodon, just as we find the same number of teeth in the 

 same species of Crocodile at all ages of the individual, no additional teeth being added 

 to the series from behind, like the true molars in the Mammalia, in the course of the 

 cliange of dentition as the animal advances to maturity. So much of the inner surface 

 of the dentary bone as is preserved entire in the Tilgate specimen, corresponds with 

 the same portion in the younger specimen from Stammerham ; no part is absolutely 

 flattened : the part sustaining the upper division of the mandibular canal has been 

 broken away. 



If we pass now to the consideration of the inferences as to the nature of the soft 

 or perishable teguments of the jaw, which are deducible from the characters of the 

 bone itself, it may be first remarked, that the disposition of the vessels and nerves, 

 supplying such teguments, differs according to their nature in different existing air- 

 breathing vertebrate animals, and the jaw-bone exhibits corresponding differences in 

 relation to such modifications of the mandibular vessels and nerves. To those who 

 may not have ready access to Cabinets of Comparative Osteology, a glance at the 

 plates of the well-known and widely distributed ' Ossemens Fossiles,' of Baron Cmaer, 

 will show that the rami of the lower jaw in Mammalia usually present one large, rarely 

 two or three, foramina, on the outside of each ramus at its fore-part ; but that, in 

 rei)tiles, as may be seen in the Crocodiles, PI. 1 ; the Lizards, PI. 16; the Tortoises, 

 PI. 11 ;'■" the nervo-vascular foramina are more numerous, smaller, and arranged, in a 

 more or less linear series along nearly the whole extent of the outside of the ramus of 

 the jaw. 



The first modification relates to the concentration of the nervous and vascular 

 influences upon thick, muscular, soft, sensitive, extensile and retractile lips, covering 

 the jaws, and extending beyond their fore part, where such lips are most developed. 

 The second modification relates to a more diffused and equable supply of the nervous 

 and vascular, but especially the latter, influences, to salivary follicles opening along the 



* The 4th editiou, 1824, torn, v, pt. ii, is here cited. 



