AND AVES OF NORTH AMERICA. 



105 



condyles. Posterior condyles separated by a deep notch, inner larger than outer (outer larger, Megalosaurus buck- 

 landli). Shaft much compressed from before backwards, and distal articulation at right angles to proximal, concave 

 on its Interior half. On the exterior face a strong crest extends along the proximal fourth of the length, not reaching 

 the head, which is the point of contact of the slender fibula, and is similar to the same in birds. 



In. 

 Length of tibia, 80.75 



Circumference proximal head, 15. 



Anteroposterior diameter do. 7.5 



Posterior transverse do. do. 5.5 



Transverse length distal condyle, 7. 



Longitudinal inner breadth, 2.5 



Circumference of shall, at middle, 10.5 



These long bones arc hollow, with thick walls of dense bone; diameter of medullary cavity at middle of tibia 

 1.5 inch. 



Left Fibula.— Twenty-four inches preserved, proximally concave and dilated; condyle curved, narrow acuminate 



oval, in profile concave, then rounded descending; length (i in., median breadth I .75 in. Just below the condyle on 

 the inside is a deep concavity with abrupt superior and lateral walls. Shaft less flattened below, but slender, reaching 

 a width of 1£ in. The fragment which occupied the most distal position which is preserved, is rather less flattened, 

 but quite convex on the outer face. It is not very unlike in general form the fibula of the ostrich, and like it is 

 continued to the tarsus, closely applied to the tibia. Its proximal half lies on a ridge of the tibia- in Laelaps, but 

 when the distal end of the latter expands, the fibula continues directly across the expansion, appressed to the anterior 

 face, in a shallow groove. 



I have given the fibula a relation the reverse of that assigned to Hadrosaurus and Iguanodon by Leidy and Owen 

 respectively, that is, I consider their inferior extremity the superior, and vice versa. This relai ion is coincident with 

 their bird-like affinities, which require a restriction of the fibula distally, not proximally. It also furnishes the 

 requisite extent of articular surface for the condyles of the femur in Laelaps and Hadrosaurus, as well as in Scelido- 

 saurus, according to Owen's plate. The head of the tibia, alone, is too narrow for the femur in the two genera first 

 mentioned. This structure accords also with Compgognathus, where the fibula is reduced distally. 



Tarsus and Metatarsus. — The distal extremity of the tibia is transverse, and much compressed, and does not ex- 

 hibit any of the usual appearances of an articular surface, neither the reptilian condyle, nor a cotyloid cavity sufficient 

 for an astragalus of the size necessary for an animal of such bulk. A hone, presenting a broad hour glass faced 

 articular surface was discovered with the other remains, and had puzzled the anatomists who had seen it. This 

 piece exhibits along its whole posterior aspect two faces, which form a reentrant angle for a fixed articulation: this 

 is found to have been applied to the extremity of the tibia exactly, and to have been fixed by strong articular liga- 

 ments. The medially constricted condyle presenting forwards and a little downwards exhibits an unusual modification 

 of the vertebrate astragalus. 



The fibula presents a long and narrow articular surface at the knee, and fitting the tibia by the concavity of its 

 inner face, becomes greatly attenuated at its distal third, where it is, in consequence of an obliquity of its direction 

 applied to the anterior face of the former bone. It may then be supposed to extend to the outer margin of the 

 astragalus, and terminate at the small calcaneuin which embraced the outer anterior extremity of the tibia, like an 

 epiphysis. In applying the astragalus, we see that a process projects from its superior margin, which when applied 

 to the face of the tibia occupies with its flat inner face :i shallow longitudinal concavity of that hone. This concavity 

 continues across the external expansion of the same, and is continuous with its outer margin in direct lino with the posi- 

 tion of the fibula. The continually increasing slenderncss of the tibia as represented by a large fragment of its distal 

 portion, renders it extremely improbable that it spanned the concave outline of the tibia, to be in contact as in reptiles, 

 with the distal extremity of the tibia, in the usual position of the malleolus, especially as there is no face for contact 

 on the latter. Continued from its point of obvious contact with the external margin of the tibia, it falls nearly into the 

 shallow groove mentioned and into the line of the ascending portion of the astragalus. The latter is broken off at the 

 extremity, but presents a form not very different from the broken slender end of the fibula, and is of about the same size. 

 AMKllI. PHILOSO. SOC. — VOL. XIV. 27 



