244 



KNOWLEDGE 



[November 1, 1890. 



its upper end. Now tliis (ype of pelvis is found, at the 

 present day, only among birds, that of lizards and croco- 

 diles hein": quite ditJ'erent. If, however, we turn to the 

 figure of the skeleton of the Iguanodon given in the first 

 half of this article, we shall find, as briefly mentioned there, 

 that the pubis and ischium (seen to the right of the leg) 

 run parallel to one another, and are directed backwards 

 after the fashion obtaining in birds. It is tiue, indeed, 

 that in the Iguanodon the pubis is shorter than the 

 ischium ; and it also gives o6 a large anterior plate (seen to 

 the left of the leg) corresponding to the small process ji' 

 in the pelvis of the Kiwi. These, however, are but minor 

 points of difierence which do not affect the fundamental 



Fig. G. — Left Side of the Pelvis of the Megalosaur. jijth 

 niitural size. Letters as in Fig. 5. (After Marsh). 



identity of plan. Again, the haunch-bone of the 

 Iguanodon extends far in advance of the cup for the head 

 of the thigh-bone, and thus once more follows (or, as we 

 should rather say, leads) the bird fashion. These peculiari- 

 ties in the structure of the pelvis of the Iguanodon, coupled 

 with other features in its organisation, ought to leave no 

 doubt, in the minds of all unprejudiced observers who hold 

 the doctrine of evolution, that there is some direct affinity 

 between the extinct Giant Reptiles and the modern 

 wingless birds. 



Turning now to the pelvis of the Megalosaur, of which a 

 greatly reduced representation is eiven in Fig. 6, it will at 

 once be apparent that we have to do with a widely ditierent 

 type of structure. Thus we notice, in the first place, that 

 the haunch-bone extends but a comparatively short dis- 

 tance in fi'ont of the cup for the head of the thigh-bone. 

 Then, again, — and this is by far the most important 

 feature — the pubis is directed forwards instead of back- 

 wards, and thus, instead of lying parallel with the ischium, 

 is placed at a very open angle to that bone. This form of 

 pehds, although differing in some details, is, indeed, of 

 the general type of that obtaining in modern crocodiles ; 

 and thus serves to show that in this respect the Megalo- 

 saur (and likewise the Hoplosaur) were more nearly related 

 to ordinary reptiles, and less closely to birds, than is the 

 case with the Iguanodon. 



If, however, we were led to conclude from the foregoing 



facts that the Jlegalosaur presented no closer indications of 

 affinity with birds than is exhibited by modern crocodiles, 

 we should be grievously in error; for not only does it 

 exhibit such a relationship, but exhibits it in a manner 

 which is not displayed by the Iguanodon. In this respect 

 we have, therefore, an excellent illustration of that extreme 

 complexity in the mutual relationships of extinct animals, 

 which should serve as a warning against hasty conclusions 

 as to any one extinct type having been the actual ancestor 

 of an existing creature. 



The relationship of the Megalosaur to birds is best ex- 

 emplified by certain features in the form and connection of 

 the bones of the lower leg and ankle, in attempting to ex- 

 plain which we must again crave the reader's pardon for 

 the introduction of a certain number of unavoidable 

 technicalities. 



Most of us are probably aware that our own ankle con- 

 sists of two rows of small bones, of which the upper row 

 includes the heel-bone, and the ankle-bone (corresponding 

 to the well known " huckle-bone " of a leg of mutton) ; 

 while the lower row has four smaller bones. Now in 

 moving the foot on the leg, as in the 

 action of walking, it is evident to aU 

 of us that the joint is situated between 

 the two long-bones of the leg and the 

 upper row of the ankle, i.e. the heel- 

 bone and ankle-bone. In a crocodile, 

 on the contrary, the ankle joint occurs 

 between the upper and the lower 

 rows of the ankle, so that the heel- 

 bone and the ankle-bone move with 

 the leg-bones. In a bird there is 

 yet one step further on this, for not 

 only does the movable joint occur 

 between the upper and the lower 

 rows of the ankle, but the ankle-bone 

 and the heel-bone are respectively 

 united with the two long-bones of the 

 leg, so as to form practically single 

 bones ; while the bones of the lower row of the anlfle 

 similarly unite with the long-bone supporting the toes, 

 so as to form that single slender bone, with three puUey- 

 like lower surfaces, with which we are all familiar in the 

 leg of a fowl. An adult bird, therefore, while ha^•ing 

 an ankle-joint, has no separate ankle-bone. ■' In a young 

 bird, however, as we may see for ourselves in the case of 

 a young fowl on our dinner-table, the lower end of the so- 

 called "drumstick," or mam bone of the leg, is incom- 

 pletely united to the bone itself, so that it can be readily 

 detached ; tliis detachable portion being, in fact, the bkd's 

 true ankle-bone. 



Now in the crocodile, as we have already mentioned, the 

 ankle-bone, although moving ^dth the leg-bone, remains 

 perfectly separate therefrom ; but in the Megalosaur we 

 find a condition exactly intermediate between that ob- 

 taining in the crocodile and the adult bird. This will be 

 apparent from Fig. 7, where we see the lower end of the 

 leg-bone of the Megalosaur with the ankle-bone closely 

 applied to it, and probably immovably united thereto 

 during life by cartilage. This condition is, indeed, precisely 

 similar to that which exists in the young fowl ; and thus we 

 have, so to speak, displayed before us the actual manner in 

 which the leg of a reptile has become converted into that 

 of a bird, the young bird carrying with it the history of its 

 origin fully apparent to aU who wiU but read Nature's 



* The reader will be assisted in this description by turning to the 

 figure of the bones of a bird's leg. given on page 230 of the preceding 

 number of Knowledge, 



Fiu. 7. — The Lower 

 End of the Leg- 

 bone OF THE Me- 

 galosaur, WITH 

 THE Ankle - bone 



ATTACHED TO IT. 



(After Gaudry.) 



