106 PROGRESS OF MICROSCOPICAL SCIENCE. 



compared to the following scheme : an hour-ghiss shaped cartilaginous 

 bone is suspended in a cylindrical tube — the periosteum ; that part of 

 the space of the tube which is not occupied by the former is filled out 

 by periosteal bone. This arrangement, although not found in all 

 stages, is always present in a certain stage of the development of the 

 bone. If one examine in a longitudinal section above mentioned the 

 line of ossification, which represents at the same time the boundary 

 between the cartilage and bone, there is found at the extremities of 

 that line a notch penetrating into the cartilage. It is very easily 

 understood that this notch represents the transverse section through a 

 circular groove. From the convexity of this notch (" encoche d'ossifi- 

 cation "), fibres take their origin, which, at their basis being identical 

 with the matrix of the cartilage, bend round to the side of the 

 embiyonal bone and penetrate into the latter. These fibres, which 

 Eanvier calls " fibres arciformes," become in time identical with those 

 fibres known as Sharpey's fibres. Amongst the mammalian animals, 

 the embryonal bones of sheep are best suited for the study of those 

 fibres. As soon as these fibres have left the cartilage, they appear to 

 be separated by rows of spherical or slightly polyhedral cells, which 

 Eanvier believes to be derived from cartilage cells after their capsules 

 have become opened. These cells gradually assume the characters of 

 osteoblasts, and they lie all along the arched fibres, the latter becoming 

 covered with bone substance, and thus representing the first traces of 

 subperiosteal bone. The arched fibres represent the directing fibres 

 of the ossification ; they can be recognized in the interior of the bone 

 in transverse sections, where they appear as small dotted circles in 

 the systems of the intermediary lamellae. 



On the external surface of that part of the cartilage belonging to 

 the " encoche d'ossification," a primary osseous lamella is formed, which 

 Eanvier calls the perichondral bone-crust ; it forms later on the 

 boundary between the cartilaginous and the periosteal bone. 



Variation in the Condition of the External Sense Organs in Foetal Pigs 

 of the same Litter. Mr. Burt G. Wilder, of Ithaca, N. Y.. says that in 

 comparing foetal mammals of imknown age, it is natural to estimate 

 their relative age, partly according to the degree of closure of the lids 

 and the direction of the pinnae ; since it is known that the former are 

 at first mere folds above and below the uncovered balls, which are 

 gradually covered by them : and that the pinnae are first formed as 

 little triangular folds behind the meatus, which at first jDroject dii-ectly 

 forward, and then, as they increase in size, gradually rise to the erect 

 position, and only later are retroverted upon the neck. 



"While forming a collection of foetal pigs at the large abattoir of 

 J. P. Squiers in East Cambridge, Mass., during the summer of 1872, 

 I compared the individuals of the same litter, carefully avoiding any 

 artificial displacement of the parts. 



In the five pigs of the same litter* having an average length from 

 vertex to anus of "067, mm., and an average weight of ,017*5 grams, 



* Marked 296 to 300 on the Catalogue of Neurology and Embryology of Domesti- 

 cated Animals at the Museum of Ck)mparative Zoology, Cambridge, Mass. 



