PHYSIOLOGICSL MARROW OSSIFICATION I N F E M A L E PIGEONS PRESTON RYES A S D TRUMAN S. POTTER' Laboratory of Preventive Nedicine, The DTLiversity of Chicago Structural changes occur in the bone marrox of female pigeons which are not fonnd in the male. Such changes are, essentially, variations in ossification of thc marrow and arc coincident with changes in the ovary. Our observations mere made npon the red r ~ i a r r oof~ the long bones of the leg and extending over a period of 2 years relate to 850 pigeons-449 male a i d 401 female. Obseruations were made in all months of the %year period. By gently splintering the shaft o€ the femur freshly removed form a male pigeon, thc marrow may be exposed in sitn as a dark red, moist, pulpy cord completely filling the mcdullary cavity. KO appreciable attachmcni of this cord to the inner surface of the shaft exists and the marrow may be removed in toto, exposing the inner surface of the bone a s smooth and glistening. This condition is constant for all male pigeons. Tn sharp contrast to the uniformity of the marrow pattern thus presented in the male is the extreme individual variation seen in the female. For although a considerable number of females killed a t random present a marrow pattern indistinguishable from that of the male, an equal number show an ossification of the marrow. Histologically, this is a true ossification displaj-ing lamellation and haversian canals. The degree of ossification in the female differs markedly in individual instances. In certain females it is slight and is limited Seymour Conian Fellow of Preventive Meclicine. 377 THE ANATOIIICAL RECORD. V O L . 6 0 , NO. NOVEMBER, 1934 4, AND SUPPLEMZNT 378 PRESTOIS IEYFS AND TRUMAN S. POTTER t o delicate spicules of bone extending from the inner surface of the shaft a short distance into the marrow. I n such instances the removal of the marrow exposes the wall of the medulla as a rough granular surface in contrast t o the smooth glistening surface seen in the male. In certain other females delicate trubeculae of bone extend well into the marrow and the marrow cannot be stripped from the medullary canal. With this medium degree of ossification, the marrow remains moist artd of dark red color. I n those females where tlhe ossification is maximal, anastomosing trabeculae of bone extend in every direction througout the medulla, the marrow proper being enmeshed in the interstices of the bony network. The marrow is relatively dry, its color is gray and the texture is chalky. While for convenience in description the above degrees of slight, medium, and extreme ossification are cited, all intermediate degrees of ossification occur with the shading of the one group into the next. Of the 449 males observed, none showed a marrow ossified in any degree. Of the 401 females observed, 215 showed marrow without ossification ; 112 showed slight o r medium marrow ossification and 74 c;howed extreme ossification. The fact that the bone marrow of female pigeon undergoes osseous modifications which do not occur in the male is of less import than the fact that these changes are cyclic and parallel functional changes of the ovary. The degree of ossification varies directly with the size of the developing ovarian follicles. Thus when the ovary contains no follicle of a. diameter greater than 2 mm. there is no ossification of the marrow. Rut when thc ovary contains a follicle of more than 4.5 mm. in diameter, there is always some degree of ossification of the marrow and when a 10-mm. follicle is present there is always extreme ossification of the marrow. Systematic measurement was made of the diameter of the largest ovarian follicle found in each of 298 females and these diameters averaged f o r each of the three groups showing : no ossification, medium ossification and extreme ossi- MARROW OSSIFICATION IN FEMALE P I G E O N S 379 fication: the mean diameter of the maturest follicle i n those females with n o marrow ossification was 1.6 mm. ; f o r those with medium ossification, 4.1 mm. and for those displaying extreme ossification, 9.1 mm. W e conclude from these findings that in female pigeons there is a cyclic ossification of the red marrow of the long bones of the leg and that the ossification is coincident with the maturation of the ovarian follicle.