36 



SCIENCE 



[N. S. Vol. XLIII. No. 1097 



two groups we may use the facts, in the worts 

 aboYe referred to, to explain conditions in the 

 Cretaceous plesiosaurs which are inexplicable 

 on any other grounds. 



The limb bones of adult plesiosatu-s are 

 solid. Young bones nearly always exhibit the 

 canal, cavity and one or more of the foramina 

 above referred to. The fact that the bones 

 are first hollow and later become solid would 

 seem to indicate that the osteolytic elements 

 present in the limb bones of mammals and 

 most reptiles were almost absent, or present in 

 small numbers, in the plesiosaurs and many of 

 the larger dinosaurs. 



If the comparison between the developing 

 limb bones of mammals and reptiles is a safe 

 one, then we have here in the young aquatic 

 plesiosaurs of the Cretaceous a condition which 

 persisted until late in life and which recurs 

 in the young of all mammals at the present 

 day. One species of plesiosaur, based on an 

 immature skeleton of an animal some fifteen 

 feet in length, exhibits these conditions in a 

 v/ell-marked manner. Through the openings 

 in the edges of the limb bones of the plesi- 

 osaurs, as in the mammals, migrated the 

 osteoblasts or bone-forming cells, the blood 

 vessels and other elements. 



The peripheral or perichondral bone was 

 formed first in the plesiosaurs as in the mod- 

 ern mammals, and, through the migration of 

 the bone-forming cells inward, the so-called 

 endochondral bone was a secondary formation. 

 The formation of bone within the endochon- 

 drium of the plesiosaurs was, apparently, re- 

 tarded by some osteolytic agent, possibly the 

 osteoclasts, until the bone-forming elements 

 for some unknown reason attained the suprem- 

 acy and completely filled the medullary cavity, 

 canal and foramen with solid bone. During 

 this process of filling there resulted, in young 

 bones, a sharp line of separation of the peri- 

 chondral from endochondral bone, resulting 

 in the formation of curious conical end pieces, 

 formerly called epiphyses, but now known to 

 be the result of bone growth and not epiphyses 

 at all. 



Bidder* has offered an interesting explana- 

 tion of the formation of epiphyses in mam- 



mals, by the migration of the osteoblasts 

 through special vascular canals {Oanalis vas- 

 culosis perforans) which traverse the space be- 

 tween the medullary cavity and the cartila- 

 ginous caps at the ends of the limb bones. 



It is interesting to observe in broken and 

 sectioned plesiosaurian propodials an exactly 

 similar condition for this ancient group of 

 aquatic reptiles. The canals are found ex- 

 tending from the medullary cavity to the ends 

 where the bone has been formed in the shape 

 of small conical mounds around the vascular 

 openings, so that in the plesiosaurs the process 

 resulted not in the production of new growths 

 at the ends of the limb bones (epiphyses) but 

 in the elongation of the bone. It is hoped in 

 another place to give a fuller explanation and 

 figures of these interesting relies of Mesozoic 

 EoY L. MOODIE 



The University of Illinois, 

 Department of Anatomy, 

 Chicago, III. 



THE COLUMBUS MEETING OF THE 



AMERICAN ASSOCIATION FOR THE 



ADVANCEMENT OF SCIENCE 



The regular meeting just held at Columbus (Do- 

 ceniber 27 to January 1) was one of the most 

 successful of the recent meetings of the associa- 

 tion. All of the sessions were held in the build- 

 ings on the campus of the Ohio State University 

 and members of the association who attended the 

 Columbus meeting of 1899, and who had not vis- 

 ited the university since were surprised and de- 

 lighted at the enormous growth of the institution 

 and at the character of the many new buildings 

 which had been built since that day. The local 

 committee in charge of the arrangements was ex- 

 tremely efficient and the compactness of the group 

 of buildings and the exceptional meeting room 

 facilities made everything easy for members in at- 

 tendance. 



The opening night for addresses of welcome 

 and for the annual address of the retiring presi- 

 dent was in many respects the most impressive func- 

 tion of the kind held under the auspices of the 

 association in the recollection of the writer. In 

 spite of a stormy night the coUege chapel, seat- 

 ing about 1,200 persons, was completely filled. 

 The address of welcome by President W. O. 



