Chapter 39

[626]Brit. Assoc. Rep. 1841, p. 103.

The elaborate investigation of the fossil remains of these stupendous beings, and the luminous exposition of their organization and physiological relations, embodied in the report to which the above extract is introductory, are among the most important contributions to Palæontology, and afford a striking example of the successful application of profound anatomical knowledge to the elucidation of the most marvellous epoch in the earth’s physical history, theAge of Reptiles.

From the great size of the bones of these reptiles, their remains have excited the curiosity even of the common observer; and although an exaggerated idea has been generally entertained of the magnitude of the original animals, yet, even when reduced to their natural proportions by the rigorous formula of the anatomist, applied to the accumulated relics which years of laborious research have exhumed from their rocky sepulchres and deposited in our museums, their dimensions are sufficiently stupendous to satisfy the most enthusiastic lover of the marvellous.

Let the reader visit the British Museum,[627]and after examining the largest thigh-bone of the Iguanodon, repair to the zoological gallery, and inspect the recent Crocodilian reptiles, some twenty-five or thirty feet in length; and observe that the fossilboneequals, if not surpasses, in size, the entirethighof the largest of existing reptiles; then let him imagine this bone clothed with proportionate musclesand integuments, and reflect upon the enormous trunk which such limbs must have been destined to move and to sustain—and he will obtain a just notion of the appalling magnitude of the lizards which inhabited the country of the Iguanodon.

[627]See Fossils of the British Museum, p. 227.

The general characters of the extinct reptiles comprised in the orderDeinosauria[628]must be known to the intelligent reader, from the various popular notices which have from time to time appeared; and their names have become as familiar as household words. I shall here restrict myself to a few general remarks on the form and structure of the teeth, and of some of the more important bones of the best known species of these great reptiles.[629]

[628]In the new edition of Pictet’sPaléontologie(now in course of publication), two 4to. plates (xxiii. and xxiv.) are devoted to the illustration of the remains of these colossal reptiles.[629]For further account of the Iguanodon, seePetrif.p. 224, &c.; of the Hylæosaurus,ibid.p. 314, &c.; of the Pelorosaurus,ibid.p. 330, &c.; of the Regnosaurus,ibid.p. 333, &c.; and of the Megalosaurus,ibid.p. 328, &c.

[628]In the new edition of Pictet’sPaléontologie(now in course of publication), two 4to. plates (xxiii. and xxiv.) are devoted to the illustration of the remains of these colossal reptiles.

[629]For further account of the Iguanodon, seePetrif.p. 224, &c.; of the Hylæosaurus,ibid.p. 314, &c.; of the Pelorosaurus,ibid.p. 330, &c.; of the Regnosaurus,ibid.p. 333, &c.; and of the Megalosaurus,ibid.p. 328, &c.

Lign. 218. Megalosaurus Bucklandi.1/4nat.Great Oolite.Stonesfield, Oxfordshire.Portion of the left ramus of the lower jaw, containing several teeth in different stages of growth: inner aspect.a, a.Crowns of successional teeth.b, b.Transverse partitions of the tooth-sockets.

MEGALOSAURUS.

Lign. 219.Tooth of the Megalosaurus Bucklandi.(Nat. size.)Wealden.Tilgate Forest.

Megalosaurus(gigantic lizard)Bucklandi.Lign.218and 219.Bd.pl. xxiii.Wond.p 421.—The oolitic flag-stone of Stonesfield, in Oxfordshire, has long been celebrated for the bones and teeth of a gigantic reptile, which Dr. Buckland first described by the name ofMegalosaurus, in a highly interesting memoir (Trans. Geol. Soc.sec. ser.vol. i.), illustrated by figures of the teeth in a portion of the lower jaw, the sacrum, femur, and other bones. The remains of this reptile are also frequently discovered in the Wealden (seeFoss. Til. For.p. 67, pl. ix. figs. 2, 6). The most important relic of this great carnivorous terrestrial lizard is a portion of the right ramus of the lower jaw, containing one perfect tooth, and the germs of several teeth (Lign.218). The tooth of the Megalosaurus, (Lign.219, andPl. VI. fig. 7,) has a conical, laterally compressed crown, with the point recurved like a sabre, and the edges trenchant and finely serrated. The implantation of the teeth is very peculiar, and exhibits the dentition of the Crocodilians blended with that of the Lacertians. The jaw has an outer parapet, as in the true lizards (seeLign.205), but the teeth are fixed in distinct sockets, formed by transverse partitions, that are attached to a mesial (inner) parapet, composed of a series of triangular osseous plates; the bases of the old teeth, and the germs of the new ones, being thus enclosed and concealed. The tooth is formed of a central body of dentine, the crown having a coating enamel; and the whole an external investment of cement, which forms a thicker layer around the fang; the pulp-cavity is occupied by coarse bone, in the adult tooth. The microscopical examination shows the dentine to consist of very fine calcigerous tubes,1/28000th of an inch in diameter, without any admixture of medullarycanals, radiating from the pulp-cavity at right angles with the external surface of the tooth, and sending; off numerous secondary branches; these ultimately dilate into, or inosculate with, a stratum of calcigerous cells that separates the dentine from the enamel.[630]A thin slice of a vertical section, viewed by transmitted light, is representedPl. VI. fig. 7 b; showing the calcigerous tubes radiating from the centre, and terminating in the stratum of cells; this cellular structure is invested with a layer of enamel, and the latter with an external coat of cement, indicated by the dark outline.[631]

[630]Owen’sOdontography, p. 271, which should be consulted for more minute details.[631]To fully comprehend the minute structure of these and the other teeth figured inPl. VI.Professor Owen’s plates should be examined; the small scale necessarily adopted in the present work rendering it impossible to do justice to the subject.

[630]Owen’sOdontography, p. 271, which should be consulted for more minute details.

[631]To fully comprehend the minute structure of these and the other teeth figured inPl. VI.Professor Owen’s plates should be examined; the small scale necessarily adopted in the present work rendering it impossible to do justice to the subject.

Four specimens of the sacrum, composed of five anchylosed vertebral (Foss. Til. For.pl. xix.fig.12), have been discovered; one of these is from Tilgate Forest. The femur of the Megalosaurus has two large rounded trochanters of nearly equal size, below the head of the bone; its shaft is sub-cylindrical, and slightly bowed.

This colossal carnivorous Saurian, whose length is estimated at thirty feet, appears to have been terrestrial, and an inhabitant of the sameterra incognitaas the Iguanodon; it probably preyed on the smaller reptiles, and the young of the Iguanodon, Crocodilians, &c.

Hylæosaurus(Wealden lizard)Owenii.Wond.pl. iv. and p. 435;Geol. S. E.pl. v.—In the summer of 1832, I obtained the interesting specimen which first demonstrated the existence of the remains of another extraordinary modification of Saurian organization in the Wealden. The circumstances which led to this discovery afford an instructive lesson to the young collector.

Upon visiting a quarry in Tilgate Forest, which had yielded many organic remains, I perceived in some fragments of a large mass of stone, which had recently been broken up and thrown on the road-side, traces of numerous pieces of bone. I therefore collected all the recognisable portions of the block, and had them conveyed to my residence. The first step was to cement together those pieces that would admit of juxtaposition, and these were at length united into a block of stone five feet long, three wide, and about one foot thick. This was firmly fixed in a stout frame, to prevent the separation of the united portions during the process of chiselling. Guided by the indications which the sections visible on the edge afforded, a thin iron wedge was carefully driven in, about half an inch above the uppermost layer of bones, and a large slab was flaked off; the three dermal spines (Wond.pl. iv. 5) in the middle of the specimen were thus exposed, and shivered to pieces; some fragments adhered to the mass broken off, others to the block, and many were detached; every piece, however small, was collected, and those adhering to the slab were chiselled out; and the whole were then carefully replaced and cemented to the bones that remained imbedded in the large block. After an interval of some days, to allow of the firm cohesion of the cemented parts, the task was resumed, and the stone chiselled away, until some portion of the large bones of the pectoral arch (Wond.pl. iv. 7) were observed. The specimen was at length brought to the state in which it now appears (in the British Museum[632]); but during the progress of its development, which occupied many weeks, it was repeatedly necessary to suspend the work, and unite displaced fragments of bone, and resume the task after their consolidation. The plate in theGeol. S. E.conveys a good idea of the original.

[632]SeeFossils, Brit. Mus.p. 139, &c.

The specimen consists of a part of the spinal column, composed of seven dorsal and three or four cervical vertebræ, almost in their natural juxtaposition, with obscure indications of a part of the base of the skull; eleven ribs; the bones of the pectoral arch (twocoracoidsand twoscapulæ); with numerous dermal bones and spines. A second specimen of this reptile was found near Bolney, in Sussex; and like the former, it was, unfortunately, almost wholly destroyed by the labourers; but I obtained many bones, some of which are perfect, and indicate an animal of considerablemagnitude: ascapula, nineteen inches long, an arm-bone orhumerus, numerous ribs, bones of the phalanges, &c. A fine series of twenty-six caudal vertebra, having a total length of nearly six feet, with chevron bones and dermal spines, was discovered in 1837, in Tilgate Forest.[633]A few detached bones are the only other relics of this reptile that have come under my observation.[634]The osteological characters presented by these remains afford another example of tire blending of the Crocodilian with the Lacertian type of structure; for we have in the pectoral arch the scapula or omoplate of a crocodile associated with the coracoid of a lizard. Another remarkable feature in these fossils is the presence of the large angular bones or spines (described p. 660, figuredLign.208), which, there is reason to infer, constituted a serrated crest along the middle of the back: and the numerous small oval dermal bones, which appear to have been arranged in longitudinal series along each side of the dorsal fringe. (Geol. S. E.p. 323.)

[633]SeeFossils, Brit. Mus.p. 323.[634]See "Memoir on the Remains of the Iguanodon, Hylæosaurus, and other Saurian Reptiles," by the Author, inPhilosophical Transactionsfor 1841, Part II.

[633]SeeFossils, Brit. Mus.p. 323.

[634]See "Memoir on the Remains of the Iguanodon, Hylæosaurus, and other Saurian Reptiles," by the Author, inPhilosophical Transactionsfor 1841, Part II.

The vertebræ, ribs, and other parts of the skeleton found in these specimens also present modifications of structure of great interest.[635]No specimens of teeth have been found associated with the remains of the Hylæosaurus, in such manner as to afford unequivocal proof of their belonging to that animal. But in the same quarries, teeth, decidedly of the Lacertian structure, are occasionally found, and may with some probability be referred to that reptile. These teeth (seePl. VI. fig. 6a.) are about 11/4inch in length, and commence at the base with a cylindrical shank, which gradually enlarges into a crown of an obtuse lanceolate form,convex in front, hollowed behind, and terminating in a rounded obtusely angular apex, the margins of which are generally more or less worn.[636]The crown is solid, but the fang encloses a small pulp-cavity; the surface is enamelled, and covered with very fine longitudinal striæ; the base in every specimen appears broken transversely, as if it had been anchylosed to the jaw, or to the base of a socket. The fang never presents an appearance of lateral adhesion, as if belonging to a Pleurodont lizard. Sections of these teeth expose a simple, central, medullary canal, the upper part of which is generally filled with the ossified remains of the pulp; and this is surrounded by a body of firm dentine, with extremely minute calcigerous tubes radiating from the centre to the periphery of the tooth, which is invested with a relatively thick coat of enamel, in which no structure is apparent.Pl. VI. fig. 6brepresents a small portion of a vertical slice, highly magnified and viewed by transmitted light. The reference of these dental organs to the Hylæosaurus must not, however, be considered as conclusive, until confirmed by the discovery of the teeth attached to the jaw, in connexion with other parts of the skeleton. The locomotive organs of the Hylæosaurus are but imperfectly known; a perfect humerus, one phalangeal bone, and fragments of the fibula (the small bone of the leg) are the only bones hitherto observed. The length of this reptile, which was probably terrestrial and herbivorous, may be estimated at from twenty to thirty feet.

[635]See Report, Brit. Assoc. 1841, pp. 111-120. Phil. Trans. 1841, pp. 141-144, pl. x.[636]Rep. Brit. Assoc. 1841, p. 118. Geol. S. E. England, pl. ii. figs. 2, 4. Phil. Trans. 1841, p. 144, pl. vi. figs. 9, 10, 11.

[635]See Report, Brit. Assoc. 1841, pp. 111-120. Phil. Trans. 1841, pp. 141-144, pl. x.

[636]Rep. Brit. Assoc. 1841, p. 118. Geol. S. E. England, pl. ii. figs. 2, 4. Phil. Trans. 1841, p. 144, pl. vi. figs. 9, 10, 11.

Iguanodon.Ligns.219to226;Wond.pl. ii. iii., and pp. 422, &c.—Soon after my first discovery of the remains of vertebrated animals in the strata of Tilgate Forest, some teeth of a very remarkable character particularly engaged my attention, from their dissimilarity to any that had previouslycome under my notice.[637]Attention having been directed to these interesting fossils, examples were soon discovered of teeth in various conditions, from the sharp, unused tooth of the young reptile, to the obtuse, worn-out crown of the adult. From the resemblance of the perfect teeth to those of the Iguana (Lign.205, p. 649), a land lizard of the West Indies, I proposed the name ofIguanodon(signifying an animal with teeth like those of the Iguana) for the extinct reptile to which they belonged. The numerous bones and teeth subsequently exhumed from the strata of Tilgate Forest and other localities in the Wealden of Sussex and of the Isle of Wight, and the considerable portion of the skeleton of an individual discovered by Mr. Bensted in the Kentish Rag, have supplied the data upon which our present knowledge of the characters of the original is based.

[637]These are described inFoss. South D.1822, p. 54, under the head "Teeth and bones of unknown animals." This was the earliest published notice of the fossils of the Wealden; it contains also a description of a tooth of the Megalosaurus (p. 55, No. 42).

In Wond, pp. 422-435, a brief account will be found of the character of the teeth, horn, femur, vertebræ, &c., and of the Maidstone specimen[638](Pl. III.).

[638]In a Monograph on the Reptiles of the Cretaceous Deposits of England, published by the Palæontographical Society, Professor Owen has lately figured anew and described in detail this most valuable fossil skeleton; to which description are appended the Professor’s latest views on the structure of the teeth of this reptile.

The "Geology of the South-east of England" contains accurate figures of the long bones of the leg (Geol. S. E.pl. ii), femur, clavicles (Geol. S. E.pl. iv.), tympanic bone (Geol. S. E.pl. ii.), horn and ungual bone (Geol. S. E.pl. iii.). In the "Fossils of Tilgate Forest," there are fifteen quarto plates devoted to the illustration of the bones and teeth of the Iguanodon and other Wealden reptiles. The osteological structure is fully detailed inRep. Brit. Assoc.1841, pp. 120-144. A general notice of the principal bones of the Iguanodon, with plates, will be found inPhil. Trans.1841, pp. 131-151; and inPetrif.chap. iii. the author has given a detailed account of the most important specimens, both in the British Museum and in his own collection, together with a résumé of the palæontology and geology of the Wealden district.

Lign. 220. Iguanodon Mantelli.1/7nat. size.Wealden.Tilgate Forest.The right ramus of the Dower Jaw;[639]discovered in 1848, by Captain Lambart Brickenden, F.G.S.Fig.1.—The inner aspect, showing three teeth, and the sockets of eighteen.a.Germ of a tooth.b.Perfect crown of a successional tooth.c.Remains of a successional tooth, the upper part having been broken off.d.The symphysial extremity of the jaw.e.The opercular furrow.f.The coronoid process.2.—3, and 4, the teetha,b, andc, infig.1, represented on a larger scale.

[639]For the outer aspect, and a restoration of the whole jaw,Petrif.pp. 247 and 249.

Lign. 221. Lower Tooth of the Iguanodon:nat. size.Wealden.Tilgate Forest.The apex slightly worn.Fig.1.—Inner aspect, showing the longitudinal ridges, and denticulated margins of the crown of the tooth.2.—View of the outer surface of the tooth.a.The denticulated margin.b.The apex of the crown, worn by use; b.fig.2, shows the oblique smooth surface produced by mastication.c.A transverse fracture of the fang, showing a section of the medullary cavity occupied by the ossified remains of the pulp.d.Marks the inferior limit of the denticulated margin; if a line were carried horizontally from d, across the tooth, the under figure would represent a tooth worn flown below the denticulations, and deprived of its peculiar dental characters; in this latter state the tooth somewhat resembles an incisor of a Rhinoceros (seeLigns.222,223; andPetrif.Lign.48).

Lign. 222. Upper Tooth of the Iguanodon:nat. size.Wealden.Brook Bay, Isle of Wight.The crown is worn down to an oblique smooth surface, and the fang is absorbed.

Jaw and Teeth of the Iguanodon.Ligns.219-223.—Although the form and structure of the cranium are unknown, yet the half of a lower jaw, discovered in Sussex by Capt. L. Brickenden,[640]and a fragment of an upper jaw, found some years since,[641]enable us to form a tolerably perfectidea of the structure and functions of the dental organs of the Iguanodon. The unused tooth of this reptile is characterized by the prismatic form of the crown, the presence of from two to four longitudinal ridges on its enamelled face, the denticulated margins (Lign.221,a), and finely serrated edge of the summit, as seen inLign.220,fig.3. The shank or fang of the tooth (Ligns.221,223,fig.2) is sub-cylindrical, slightly curved, and tapers to a point. The inner surface of the crown in the lower teeth, and the outer surface in the upper, are covered with a thick layer of enamel, but the opposite face of the crown and the sides have but a thin coating of this substance. The teeth of the upper jaw (Lign.222) are curved in the opposite direction to those of the lower, and have the convexity external, and the concavity internal. Thus the upper and lower molars were related to each other nearly as in the Ruminants; the outer aspect below corresponding to the inner above (seePetrif.Lign.56, p. 254). The specimens met with have almost always the apex of the crown more or less worn down by use[642](seeLign.223), and presenting an oblique, triangular, smooth surface, as in the fine large specimen figured inLign.221, which was foundimbedded in the trunk of a Clathraria, as if it had snapped off while the animal was in the act of gnawing the tough stem. The denticulated margins are well developed; infig.1, they appear as simple serrations; but viewed laterally,they are seen to be formed by a series of denticulated plates (Lign.223,fig.6). The crown of a tooth of a young animal, worn at the summit, and presenting but three longitudinal ridges, is representedPl. VI. fig. 4a. The microscropical structure consists of a simple pulp-cavity in the centre of a body of dentine permeated by calcigerous tubes, but with this peculiar modification, that the dentine is traversed by vascular canals, radiating at definite intervals from the pulp-cavity nearly to the periphery of the tooth, and running parallel with the calcigerous tubes; thus constituting a softer and coarser dentine than in the other reptiles, and resembling that which characterizes the teeth of some of the herbivorous mammals.[643]The crown of the tooth is covered with a layer of enamel, which is thickest on the external surface: and the fang is invested with cement. The structure here described is shown inPl. VI.; fig. 4b, a vertical, andfig. 4c, a transverse section of a tooth, seen by transmitted light, with a high magnifying power. The calcigerous tubes are1/25000an inch in diameter. Sections of the teeth of the Iguanodon are beautiful objects under the microscope, for the medullary canals are generally of a deep yellowish brown colour.

[640]Figured and described in thePhil. Trans.1848, p. 188, pl. xvi. xvii.[641]Both specimens are fully described inPetrif.pp. 242,et seq.[642]Plates iv. and xvii. in the "Fossils of Tilgate Forest," contain representations of upwards of thirty specimens of teeth in various states of development and detrition.[643]Tomes on the Microscopic Structure of the Tooth of the Iguanodon,Petrif.pp. 239, 240. See also Owen’sOdontography, p. 249, and pl. lxxi.; andCycl. Anat.Art.Teeth.

[640]Figured and described in thePhil. Trans.1848, p. 188, pl. xvi. xvii.

[641]Both specimens are fully described inPetrif.pp. 242,et seq.

[642]Plates iv. and xvii. in the "Fossils of Tilgate Forest," contain representations of upwards of thirty specimens of teeth in various states of development and detrition.

[643]Tomes on the Microscopic Structure of the Tooth of the Iguanodon,Petrif.pp. 239, 240. See also Owen’sOdontography, p. 249, and pl. lxxi.; andCycl. Anat.Art.Teeth.

Lign. 223. Teeth of Iguanodon.Wealden.Tilgate Forest.Fig.1.—Outer aspect of an upper tooth (in a reversed position), worn flat, and with the fang absorbed; fig. 3, inner aspect of the same tooth.a, a.Flat grinding surface, produced by mastication when all the thickly enamelled portion of the crown is worn away.c.Cavity produced by the pressure of a new tooth.2.—Lower tooth of a young animal, slightly worn: inner aspect.4.—Outer Surface of a lower tooth of an adult; and fig. 5, inner surface of the same.a, a.The hard cutting edge of the oblique surface worn by mastication.c.Indentation produced by the pressure of a successional tooth.6.—Edge view of the serration on fig. 5; magnified.

The dentine is less vascular, and therefore hardest, on that side of the crown which has the thicker coat of enamel; hence the tooth wears away faster on one side than on the other, and an oblique grinding surface, with a sharp edge of enamel, is maintained until the crown is worn away. The internal structure of the teeth of the Iguanodon is thus in perfect accordance with their external configuration, and must have been admirably adapted, in every stage, for the laceration and comminution of the tough vegetable substanceswhich, there is every reason to conclude, constituted the food of this colossal oviparous quadruped.

Vertebra of the Iguanodon,[644]Lign.206, p. 653;Lign.224.—The remains of the vertebral column of the Iguanodon, consisting generally of broken and water-worn dorsal and caudal vertebræ, deprived of their processes and reduced to the state of the specimens representedLign.206,figs.6 and 8, are so abundant in some of the Wealden strata, that a short account of their characters may be useful. A reference toLign.206, and its description, will render the following remarks intelligible to the general reader. The vertebræ of the Iguanodon are distinguishable from those of other reptiles which occur in the same strata by the following peculiarities, which the figure of a perfect specimen of a caudal vertebra (Lign. 206,fig.3) will serve to illustrate. The body, or centrum, is either flat or somewhat depressed on both articular faces; its sides are nearly flat, or somewhat convex, vertically (as infig3), and slightly concave lengthwise, or from front to back: in some examples, the body is more contracted towards the inferior surface, as infig.6; and in the vertebræ, near the middle of the tail, the sides are compressed, so as to give an angular contour and somewhat vertical elongation to the face, as infig.4; but in the dorsal vertebræ, the articular faces are nearly circular, but somewhat higher than wide. In the caudal vertebræ, the inferior angles of the body are truncated (w,figs.3, 4), and present an oblique, smooth face, to articulate with the chevron bone (fig.3,f). The annular part is united to the body by suture (fig.3,o), and anchylosed in the dorsal vertebræ; and in these bones the neuralarch is very high, and greatly expanded, and its bases extend transversely inwards, and join each other below the spinal canal, forming a ring, or bony channel, to contain the spinal chord.[645]"The transverse processes are straight, and very long in the vertebræ from the middle of the trunk, indicating a considerable expanse of the abdominal cavity, adapted for the lodgment of the capacious viscera of a herbivorous quadruped." (Owen.) The spinous processes (Lign.206,fig.3,d) are large and of great height in the anterior caudal vertebræ,Lign.224; and here the chevrons, or hæmapophyses (Lign.224,b, andLign.206,fig.2, andfig.3,f), are also of considerable length; the bases of the latter are always united (Lign.206,fig.2,g), and often blended, so as to form but one face for articulation with the truncated inferior angles of the body of the vertebra:, leaving a vertically elongated channel for the passage of the large blood-vessels of the tail. The external surface of the vertebræ of the Iguanodon is more or less marked with fine longitudinal striæ; those of the Megalosaurus have a smoother and more polished surface.[646]

[644]A detailed account of the elements of the spinal column of the Iguanodon, and remarks on various fossil vertebræ, the relations of which with the Iguanodon have been considered doubtful, will be found inPetrif.pp. 256-279.[645]See also lithographs of dorsal and caudal vertebræ from the Kentish Rag; Owen’sMonog. Cret. Rept.(Pal. Soc.) 1851.[646]See Rep. Brit Assoc. 1841, pp. 125-133, where an elaborate investigation of the vertebra: of the Iguanodon is given by Professor Owen.

[645]See also lithographs of dorsal and caudal vertebræ from the Kentish Rag; Owen’sMonog. Cret. Rept.(Pal. Soc.) 1851.

[646]See Rep. Brit Assoc. 1841, pp. 125-133, where an elaborate investigation of the vertebra: of the Iguanodon is given by Professor Owen.

Lign. 224. Six Caudal Vertebra of the Iguanodon.1/14nat. size.Wealden.Tilgate Forest.a, a.Spinous processes (neurapophyses), from 13 to 151/2inches in height.b, b.Three displaced chevron bones (hæmapophyses), imbedded in the stone near their original position at the junction of the bodies of the vertebræ.c.Anterior articular face of a vertebra.

Bones of the Extremities.Ligns.225and226.—The thigh-bone (femur), both bones of the leg (tibiaandfibula), and many of the metatarsal and phalangeal bones have been discovered; the osteology of the hinder extremity is, therefore, almost perfect. The thigh-bone (Lign.225; andPetrif.p. 292,) is of a very remarkable character, having a closer resemblance to the femur of a huge mammalian, than to that of a reptile.[647]Several perfect specimens have been discovered, as well as the associated bones of the leg (Petrif.p. 293,Lign.62); but the first fragment that came under my notice, was the middle portion of the shaft of a femur of enormous size, and of an irregular quadrangular form; and so shapeless and unintelligible it then appeared, that several years elapsed before its real nature was determined. (Foss. Tilg. For.pl. xviii.)

[647]See Cuvier’sOssem. Foss.vol. ii. p. 36.

Lign. 225. Left Femur of the Iguanodon.1/10nat. size.Anterior aspect.Wealden.Brook Bay, Isle of Wight.a.Outer trochanter.b.Median trochanter.c.Inner condyle.d.Outer condyle.e.Anterior infra-condyloid fissure.f.Head of the femur.

An entire thigh-bone of an adult Iguanodon, from the Weald clay in the west of Sussex, measured three feet eight inches in length.[648]end thirty-five inches in circumference at the condyles; and I have a femur of a very young animal,that is but five inches long. The form of the thigh-bone is so peculiar, that fragments may easily be recognised. The head of the femur (Lign.225,f,) is hemispherical, and projects inwards; there is no appearance of aligamentum teres; a flattened process or trochanter (Lign.225,a,) forms the external boundary of the neck of the bone, from which it is separated by a deep and narrow vertical fissure; the shaft is of a sub-quadrangular shape, and a slightly elevated ridge, produced by the union of two broad, flat, longitudinal surfaces, extends down the middle of the anterior face, and, diverging towards the inner condyle, gradually disappears. The bone terminates below in two large condyles, separated in front and behind by a deep, narrow cleft, or groove (Lign.225,e). Near the middle of the inner edge of the shaft, there is a compressed ridge, with an angular projection, or trochanter. Thus the upper part of the femur maybe known by the presence of the flattened, or laterally compressed trochanter; and if that process be wanting, a fractured surface indicating its position may be detected; the middle of the shaft is characterized by its broad angular faces, and the inner submedian trochanter: the condyloid or inferior extremity of the bone may be distinguished by the deep groove between the condyles, both in front and behind.

[648]The average length of the adult femur is estimated at about four feet five inches.

The arm-bone (humerus) of the Iguanodon has been discovered in the Wealden of the Isle of Wight by Mr. Fowlstone; it is figured and described inPetrif.p. 286. The humerus is also present in the Maidstone specimen[649]of Iguanodon, before referred to at page 692: in pl. ii. ofWond.this bone is termed theradius. The humerus of this reptile is much smaller than the femur; in the Maidstone specimen the former is about 20 inches, and the latter about 33 inches in length.

[649]The two bones marked "6" in pl. ii.Wond.and inLign.65,Petrif.(one of which is figured in outline inLign.226,fig.4,) regarded by Prof. Owen as theradiusandulna(the two bones of the fore-arm): the author’s reasons for regarding these bones asmetacarpalsare given in full at p. 289,Petrif.

As separate bones of the feet of the Iguanodon, for example,metacarpals,metatarsals,phalangeals, andunguals, often occur in the strata of the Wealden, figures of several specimens, on a reduced scale, are introduced inLign.226, and may enable the student to identify those he may meet with in his researches.[650]The ungual phalanges, or claw-bones, which were invested with the nail, are sometimes found of an enormous size; from a quarry near Horsham, Mr. Holmes obtained specimens more than five inches long, and three inches wide at the articular extremity.

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