The hip-girdle of bones differs chiefly from other types in the way in which those bones, which have sometimes been likened to the marsupial bones, are conditioned. They may be a pair of triangular bones which meet in the middle line, so that there is an outer angle like the arm of a capital Y. Sometimes these triangular bones are blended into a curved, bow-shaped arch, which in several specimens appears to extend forward from near the place of articulation of the femur. This is seen in fossil skeletons at Heidelberg and Munich. It is possible that this position is an accident of preservation, and that the prepubic bones are really attached to the lower border of the pubic bones. Immense as the length of the tail appears to be, exceeding the skull and remainder of the vertebral column, it falls far short of the combined length of the phalanges of the wing finger. The power of flight was manifestly greater in Rhamphorhynchus than in other members of the group, and all the modifications of the skeleton tend towards adaptation of the animals for flying. The most remarkable modification of structure at the extremity of the tail was made known by Professor Marsh in a vertical, leaf-like expansion in this genus, which had not previously been observed (p. 161). The vertebræ go on steadily diminishing in length in the usual way, and then the ossified structures which bordered the tail bones and run parallel with the vertebræ in all the Rhamphorhynchus family, suddenly diverge downward and upward at right angles to the vertebræ, forming a vertical crest above and a corresponding keel below; and between these structures, which are identified with the neural spines and chevron bones of ordinary vertebræ, the membrane extends, giving the extremity of the tail a rudder-like feature, which, from knowledge of the construction of the tail of a child's kite, may well be thought to have had influence in directing and steadying the animal's movements. There are many minor features in the shoulder-girdle, which show that the coracoid, for example, was becoming unlike that bone in the Lias, though it still continues to have a bony union with the elongated shoulder-blade of the back. [Illustration: FIG. 56. RESTORATION OF THE SKELETON OF _RHAMPHORHYNCHUS PHYLLURUS_ From the Solenhofen Slate, partly based upon the skeleton with the wing membranes preserved] [Illustration: FIG. 57. RESTORATION OF THE SKELETON OF _SCAPHOGNATHUS CRASSIROSTRIS_ Published in the _Illustrated London News_ in 1875. In which a tail is shown on the evidence of the structure of the head and hand] [Illustration: FIG. 58. SIX RESTORATIONS 1. Ramphocephalus. Stonesfield Slate. John Phillips, 1871 2. Rhamphorhynchus. O. C. Marsh, 1882 3. Rhamphorhynchus. V. Zittel, 1882 4. Ornithostoma. Williston, 1897 5. Dimorphodon. Buckland, 1836. Tail then unknown 6. Ornithocheirus. H. G. Seeley, 1865]