1034 ME. W. p. PyCEAFT ON THE [Dec. 1&, 



These last bear ouly a roughened diapopl\ysial surface on the 

 neuroid. There is no indication of a plenrapophysial element 

 (sacral rib). If these two vertebrse are really sacral then they 

 lie more caudad than usual, being behind the acetabulum and 

 directly opposite the middle of the ilio-ischiadic foramen. The 

 characteristic lumbar enlargement lies between the 2nd lumbar in 

 front and the 1st sacral behind. 



The free caudal vertebrse vary from 6-7 in number, including 

 the pygostyle. They are very feebly developed in the Grebes, 

 Intercentra occur below the caudal vertebrae both in Colymbi and 

 Podicipides, but are reduced to mere vestiges in the former. 



The lateral compression of the synsacrum is less marked in the 

 nestling than in the adult ; and the high neural crest of the adult 

 preacetabular region is wanting in the nestling. 



V. Thjs Eibs. 



The anterior anchylosed cervical ribs in the Pygopodes, in their 

 form and position, recall those of Phalacrocorax. In the adult 

 they are completely fused above with a downgrowth from the 

 ventral surface of the anterior zygapophysis and below with the 

 anterior and ventral borders of the catapophyses so as to form a 

 bony canal for the vertebral artery. 



In the Grebes they are found only from the 2nd to the 9th 

 vertebrae, and are comparatively feeble, though long ; those of the 

 2nd vertebrae are mere vestiges. In the Divers (Colymbi) they 

 start from the 3rd vertebra, but terminate, as a pair of vestigial 

 processes on the 10th or 11th ; they differ markedly from those in 

 the Grebes by their great length and thickness, extending back- 

 wards so as to embrace the catapophyses of the vertebra next behind, 

 when the neck is straightened out. 



The posterior free cervical ribs in the Podicipides are two in 

 number (see next page). The penultimate, borne by the 21st 

 vertebra, is long, styloid, and without an uncinate ; that of the 

 22nd vertebra is longer, extending down to the level of the top 

 of the sternal rib immediately behind it. It bears a large uncinate, 

 but no sternal segment. 



In the Colymbi there is only one free cervical, apparently 

 corresponding to the antepenultimate rib of the Grebe. 



The thoracic ribs in the Podicipides are 7 in number, the last 

 two being overlapped by the ilium. 1-5, like the last cervical, 

 bear large uncinates ; these are absent on the 6th and 7th. There 

 are 8 pairs of sternal ribs, the 8th being bound by membrane to 

 the posterior border of the 7th. Thus there is evidence of the loss 

 of at least one pair of thoracic ribs. It should be remarked, by the 

 way, that the 7th pair of sternal ribs do not articulate with the 

 sternum. 



The thoracic ribs in the Colymbi number 8 pairs, all but the 

 last of which articulate with the sternum. The last 3 pairs are 

 overlapped by the preacetabular ilium. The 8th pair are mere 

 vestiges. 



