CONNECTIVE TISSUE. 251 



THE PROCESS OF OSSIFICATION IN BIRDS. BY L. SCHONEY.* 



My observations were made on a number of chickens and pigeons of 

 different ages, the cartilages of the knee-joint, preserved and decalcified in 

 chromic acid, being my subjects of study. Sagittal sections through the knee- 

 joint of birds demonstrate that the bulk of the hyaline cartilage decreases 

 with age, and that a transformation of cartilage directly into medullary ele- 

 ments and indirectly into bone takes place only in young animals. In older 

 ones completed bone-tissue bounds the cartilage, and in old pigeons the 

 medullary spaces of the bone produce elongations which at a certain height 

 penetrate the cartilage. 



In sagittal sections of young animals, we see with low powers of the 

 microscope the following: At the articular surface, and near the perichon- 

 drium, elongated, spindle-shaped cartilage corpuscles are found, which gradu- 

 ally change into globular, nucleated corpuscles. The latter are met with 

 in the middle portion of the cartilage, which is pervaded by medullary spaces, 

 containing blood-vessels. The layer of the globular, nucleated corpuscles is 

 followed by a narrow layer, in which there are small, flat cartilage corpuscles 

 of a yellow-red color, bounding the district of calcification. The calcified 

 basis-substance produces a pretty frame-work, which blends with the first- 

 formed trabeculsB of bone-tissue, surrounding the medullary spaces of the 

 epiphysis. 



With higher powers, we ascertain that the calcareous frame penetrates the 

 basis-substance of the unchanged cartilage by means of pointed ends. Within 

 the frame the cartilage corpuscles are distinctly recognizable. In many places 

 the trabeculse of bone are directly attached to the calcareous frame, the 

 feature distinguishing these formations being the bone-corpuscles of the tra- 

 beculse. The medullary spaces are filled with globular, oblong, or spindle- 

 shaped medullary elements ; besides these we often encounter protoplasmic 

 masses of varying size, either multinuclear or destitute of nuclei, but uni- 

 formly granulated. Spindle-shaped elements are most prevalent in the center 

 of the medullary space, where the spindles are in connection with blood- 

 vessels. (See Fig. 103.) 



The formation of medullary spaces is best studied in horizontal sections. 

 First we recognize that at certain intervals a dissolution of the calcified basis- 

 substance of cartilage takes place. It is true that the direct transformation 

 of the cartilage into free protoplasma, with the formation of bright lumps, 

 filling the medullary spaces, cannot be directly observed, but we may readily 

 deduce such a transformation, as all medullary spaces in the neighborhood 

 are inclosed by a calcified cartilage tissue, and the calcareous frame projects 

 into the medullary space, as if broken. 



The transition of cartilage into medullary elements is initiated by the 

 deprivation of a cartilage tissue unit or territory of its lime-salts. Adjoining 

 the zone of decalcified cartilage there is found a layer of protoplasma con- 

 sisting of numerous glistening lumps. These lumps are surrounded by a 

 light narrow rim, which is seen occasionally to be traversed by filaments. 

 The lumps bear a close resemblance to like formations in mammals, 

 which have been described under the name of " hgematoblasts." The char- 



* Extracted from the essay of Dr. L. Schb'uey, in New York. " Ueberden Ossifications- 

 process bei Vogclu." Archiv f. Mikroskop. Anatomic," Bd. xii., 1875. For the second part 

 of this publication, see page 103. 



