THE SACRUM OF THE LACERTILIA. 89 



these are separately ossified and are to be looked upon as sacral 

 ribs." Gadow (n) in his work on "Amphibia and Reptiles" 

 says : " The pelvis is attached to two vertebrae by means of 

 several ribs." I have given in the bibliography, under (10), a 

 complete list of our general works on zoology in which there is 

 any statment made concerning the sacral ribs of the Lacertilia. 

 They all agree pretty well that there are sacral ribs. 



In order to be sure that there are sacral ribs among our liv- 

 ing reptiles other than the lizards I have investigated both the 

 young and adult stages of the turtles, crocodiles and Sphenodon. 

 In a young turtle, Chelydra, 44 mm. in length, the separation 

 between the vertebral centra and their sacral ribs is clearly appar- 

 ent. In a young alligator, six inches in length, the sutures 

 between the sacral ribs and the centra afe clearly seen as they 

 are also in a specimen something over four feet in length. The 

 sutures persist in the adult of the alligator and are found in the 

 young and adult of the Gavialis gangeticus Gmel, thus com- 

 pletely disproving Cope's statement that there are no sacral ribs 

 in the crocodiles. In Sphenodon the sacral ribs are distinct. We 

 know that among the Dinosauria the sacral ribs did not fuse 

 with the centra until late in life. There is in the Field Museum 

 a specimen of a young Morosaurus, as identified by Mr. 

 Riggs, which is of considerable size, and yet the sacral ribs are 

 clearly separated from the centra. Marsh has figured a similar 

 condition in the sacrum of Morosaurus lentus on Plate XXXIII. 

 of his " Dinosaurs of North America." Hatcher in his paper on 

 Haplocanthosanrus (14) gives a lengthy and very interesting 

 discussion of the sacral ribs in the Dinosauria. He expresses 

 it as his opinion " that there are no true sacral ribs homologous 

 zvith these elements in the tailed amphibia and that the so-called ribs 

 are really homologous zvith the parapophyses or inferior branches 

 of the transverse processes." 



But Mr. Hatcher is mistaken in his conception of the homol- 

 ogy of these elements above mentioned. If it is true, as he 

 states it is, that the sacral ribs (parapophyses, Hatcher) and the 

 transverse processes of the caudal vertebrae arise from distinct 

 ossificatory centers in the sauropod dinosaurs then we have in 

 these animals a primitive condition and especially as regards the 



