74 Field Columbian Museum— Geology, Vol. II. 



ferentiated, nor are there any muscular markings. On the posterior 

 border, near where the ulnar rugosity should be, there are the open- 

 ings of two large canals, one on either side of the margin (/' and c of 

 the figures). On what seems to be the ventral surface, near the 

 front border of the bone and nearly opposite the other openings, 

 there is a large one with its mouth, as in the others, directed distally. 

 On the dorsal surface, and near the middle transversely, there is a 

 fourth opening, much smaller than the others. All of these canals 

 unite near the center of the bone in a rounded cavity or ampulla, as 

 shown in Figs. 3 and 4. In PI. XXIII, Fig. 1, a large opening is seen 

 on the posterior border below a rugose space, and another opening 

 is seen towards the front leading into a groove. This was apparently 

 a canal leading into a groove on the opposite side of the bone in the 

 uninjured specimen, with another opening corresponding to the fora- 

 men which lead into a groove shown in the photograph on the 

 exposed surface of the bone. The bone was, however, injured before 

 I studied.it, as is indicated by the restored border in the figure. 

 The posterior opening probably corresponds to the united b and c of 

 the other figures. In Fig. 2 of this plate is also seen a foramen on 

 the posterior margin of the bone (the left one of the figure). All 

 these three bones are probably humeri. Figs. 4 and 5 of the plate do 

 not show these canals; from their shape they are probably femora. 

 In Fig. 1, PI. XXII, there is seen at the lower margin a groove 

 (e), partly converted into a canal, which probably corresponds to one 

 or the other of the grooves of Fig. 1, PI. XXIII. I believe this 

 groove corresponds to the ectepicondylar groove or foramen of the 

 chelonia, lacertilia, Belodon, Champsosaurus, and some of the notho- 

 saurs and ichthyosaurs. I may add that a similar groove is sometimes 

 indicated in the humerus of the mosasaurs, as shown in PL XLIV, 

 Vol. IV of the University Geological Survey of Kansas. Why these 

 canals and grooves should disappear in the adult humerus is not 

 apparent : they are doubtless for the passage of vessels. The 

 ampulla at the junction of the four canals in the embryonic bone is 

 between the apices of two conical "epiphyses," the larger epiphysis 

 occupying the chief part of the distal portion of the bone, the smaller 

 one the proximal. The fractured specimen discloses these epiphyses 

 with a smooth rounded surface, as shown in PI. XXII, Fig. 3, 

 the outer part peeling away as does the bark from a tree. 



This ephiphysial-like method of ossification has been compared 

 with a somewhat similar structure in the Ghelonians as an evidence of 

 relationship between the two orders of reptiles. 



