HESPEBOKNIS. 31 HESPERORNIS. due to degeneracy from fully winged ancestors, slender jaws, armed with sharp recur^•ed teeth Hesperomis was more than five feet in length, resembling those of reptiles. They were set in a and if its ancestors were equally bulky their common alveolar groove ( holcodont dentition ) — wings were quite too large to use ^-n^v-^ under water, but would be folded ' ^^==c:r:; 1 close against the body when the bird dived or swam. This constant dis- use, as the race became more and more exclusively aquatic, would per- mit the wings to dwindle. By the time the wings were small enough to be of use as paddles under water, as modern auks use theirs, the muscles had become too feeble to move them in so dense a medium, and so degeneration continued until only a remnant of humerus re- mained. Correlative with this was a constant growth and strengthen- ing of the legs, which became of great size (though the bones re- mained hollow, like those of an aerial bird) and so twisted as to turn edgewise when the foot was brought forward after each stroke, thus offering least resistance to the compabisos of skclls axd bbaixs. water. The original skeleton set up l. SkuU and brain-eavit.v ot Bes/jerornia regalis. from above. 2. Skull bv Marsh, and depicted in his Odon- """l braln-cavlt.v of modern loon. 3. Cast o« brain-cavity of a young ii.rnithpQ stnnH prpf>f 1ik-p t nnncniin a"'?ator; ol, olfactory lobes; c. cerebral bemiapheree: op, optic lobes; roMiiffles, stooa erect like a penguin, ci, cerebellum; /. flocculi; ra. medulla. (After Marsh.)
hen an attempt was made at the
National Museum to mount another skeleton in a fact which differentiates Hesperomis from the a swimming attitude, it was discovered that this higher Ichthyornis and its relatives, whose teeth position required an altogether novel arrange- ment of the legs, such as is shown in the ac- companying sketch of a restoration based by Lucas (see above) upon this skeleton. It ap- 6KULL AXD TOOTHKD BEAK OF HESPERGBN'IS REGALIS. pears that the legs of this bird must have stood out almost at right angles, and have acted like a pair of oars. To this most powerful apparatus for swim- ming and chase was added the best of means for were implanted in separate sockets (thecodont). (See BiBD, Fossn,.) In the upper jaw the- teeth were confined to the maxillary bone alone, but in the lower jaw they extended to the tip of the ramus. As this lower jaw was united in front only by a cartilage, as a serpent's, and had on each side a joint which admitted of some elbow-like motion, the power of swallowing was very extensive. The skull, though shaped like that of a loon, had many struthious characters, and the brain was distinctly reptilian in form, and only about one-third as large as that of a modern loon. The skeleton as a whole closely A TOOTH w : PEROKNIti. a, crown; ft. root; e, absorbed cavity in the root, oou- taininp; a young tooth (d). SHOCLDER-GIRDLE. Hesperomis rejjalis : 8, sca- pula; ft, humerus; f. clavicle, or furculum; c, coracoid; sf, sternum. seizing and holding the agile, slippery, and often bone-incased prey, in the form of a long neck, capable of rapid flexure and thrust, and long 110.VE8 OF THE TAIL. Caudal vertebrte ot Hesperomis regalis, seen from above) a, anterior convex face of Urstcaudal; b. tranverse procees. approximates that of modem birds. The verte- bra> resemble those of a loon. The shoulder- girdle, in its original structure, as well as in its degeneracy, and the sternum, which has no keel, are ostricli-like; and it is in the pelvic arch more than el.sewhere that traces of reptilian ancestry are evident. Tlie tail contained 12 vertebra — more than are or have been possessed by any other known bird since .Vrclwopteryx; and they were solid, firmly locked together and ^vinged, so that the outline of the caudal skeleton is spatulate. This, with the evidentiv strong musculature, would give great power, similar to that of a bea- ver's tail, and doubtless the organ was an impor- tant aid in swimming, by a sculling motion, as well as in steering and controlling progress.
