OCR Text |
Show 1899.] OSTEOLOGY OF T H E PYGOPODES. 1043 GROUP b. (Type P. fluviatUis.) Temporal fossa ill-defined; cerebral prominence small; fossa for insertion of temporalis muscle not deeply excavated on postorbital region of frontals ; with a small postorbital process; upper jaw not longer than cranium. Podicipes. B. With abroad bifid, overhanging postorbital process Mchmcrphorus. B. VERTEBRCE. Emargination of neural arches of cervical vertebrae caudad, slight, never extending forward beyond the level of the postzygapophyses ; anterior cervical ribs of great length ; all cervicals save atlas and axis with a bony vertebrarterial canal closed externally by the cervical ribs; synsacrum elongated, and laterally compressed, so as to be ahno6t styliform. A. Neural spines of anterior cervicals in form of long median ridge ; hyperapophyses of anterior cervicals widely separated ; neural arch of 2nd, 3rd, and 4th with a rounded free posterior border. All thoracic vertebrae free, the lst-3rd with long J_-shaped hypapophyses; 6 free caudals, excluding the pygostyle; pygostyle broad and strong COLYMBID^E. B. Neural spines of anterior cervicals almost obsolete : catapophyses of anterior cervicals meeting in the middle line; last cervico-thoracic and thoracic 1-4 anchylosed; free end of hypapophyses scarcely, if at all, laterally expanded ; 7 free caudals, excluding pygostyle; pygostyle feeble. PODICIPEDIDcE. It is almost impossible to distinguish, in the synsacrum, lumbar, lumbosacral, and sacral vertebrae. The lumbar region has apparently undergone a great shortening. There are no vertebrae which can be distinguished-in the dried skeleton-as sacral. The postsynsacral region-that lying behind the acetabulum-is of great length. The vertebral formula must therefore stand as follows:- Syn. sc. . _A Cv.13. Cv. th.l. Th.6+2. L. Lb. sc. Sc.?5. Cd. 10+7=44. > , ' ' , ' 8 17 Colymbidce. Syn. sc. Cv.20. Cv. th.2. Th.6+1. L. 4. Lb.sc.3. Sc.2. Cd. 6+7=51. 7 13 Podieipedide. C. STFRNUM AND PECTORAL GIRDLE. Corpus sterni with a pair of notches posteriorly; coracoid grooves deep; metasternum either notched posteriorly, or broadly linguiform, and projecting far beyond posterior lateral processes; anterior lateral processes not projecting forwards beyond the level of the coracoid grooves; no supracoracoid foramen ; clavicle not articulating by a glenoid surface with acromion of scapula. A Greatest width of sternum across anterior lateral processes rather less than A the length ; coracoid groove moderately deep ; spina externa sessile and bifid • keel very shallow; metasternum linguiform, projecting far beyond level of posterior lateral processes ; precoracoid very small; posterior lateral processes of coracoid large and spinose COLYMBIDCE. |