68 Ossification Process in Birds, dc. By Dr. L. Schbney. 
vertical and horizontal sections of cartilage and bone, principally 
of the knee-joint. A number of these sections were cleared with 
glycerine, and therein preserved (a method which I prefer to alco- 
holic or turpentine treatment, and preservation in balsam, because 
the clearing in the latter case will soon reach such a degree as 
effectually to interfere with the study of the more delicate tissues). 
My observations and drawings have been made with Perick's 
objectives 5, 9, and 10 (immersion) ; the drawings are not made 
diagramatically, but with the utmost possible fidelity direct from 
the preparation. For greater clearness I shall state my observa- 
tions in two sections ; the first treating of the ossification, the 
second of the new formation of red blood-corpuscles. 
I. The Ossification Process. 
Heinrich Miiller,* as we know, was the first who denied the 
direct transformation of cartilage into bone tissue ; but who would 
have instead marrow formation precede the bone formation. 
C. Heitzmann -f especially (this view having since repeatedly been 
confirmed) maintained the transformation of cartilage tissue into 
marrow tissue, this having been preceded by the deposit of lime, 
and the solution of the elementary substance ; and besides developed 
a theory of bone formation which most closely coincided with his 
view of the structure of cartilage and bone. 
He proved the existence of a rich net of living matter in the 
interior of the elementary substance of the hyaline cartilage, and 
showed that all the cartilage corpuscles (cartilage cells) are united 
in one uninterrupted mass. According to him, the solution of the 
elementary substance would be the only thing required to render 
chondrin-infiltrated-protoplasm again visible, by which the same 
would be divided into new elements, known as " marrow-cells." 
These elements themselves, however, are directly connected with 
one another by living matter, even where there has been formed an 
apparently structureless soft elementary substance (mucine ?). 
Vertical sections through the knee-joints of birds of various 
ages show, in the first place, in accordance with C. Heitzmann's 
observations on dogs, cats, and rabbits, that with increasing age 
the cartilage mass decreases in circumference (volume) ; next, 
that the transformation of the cartilage directly into marrow 
elements, and indirectly into bone, takes place only in young 
animals, whilst in older ones the ready-made bone directly joins 
the cartilage, and in fully-grown pigeons the marrow-spaces of the 
bone form prolongations which extend into the cartilage to a 
certain height. 
* • Zeitschrift fiir wissensh. Zoologie,' 7 Band, 
t ' Wiener med. Fahrb.' 1872. 
