!3UI 
THE 
JANUARY 1, 1875. 
I . — On the Development of the Smaller Blood-vessels in the 
Human Embryo. 
By Dr. H. D. Schmidt, of New Orleans, U.S.A. 
( Read before the IIoyal Microscopical Society, Dec. 2, 1874.) 
Plates LXXXVII., LXXXVIII., LXXXIX., and XC. 
The researches upon the formation and development of the smaller 
blood-vessels in the human embryo, described in the following 
pages, were made some years ago simultaneously and on the same 
material with those upon the origin and development of the blood- 
' corpuscles in man, published in the February number, 1874, of this 
Journal. The coloured blood-corpuscles, as set forth in that article, 
were found to originate within certain primary follicles in the 
wall of the umbilical vesicle which, in this instance, was attached 
EXPLANATION OF PLATES LXXXVII., LXXXVIIL, LXXXIX., and XC. 
Fig. 1. — Fragment of the chorion of the small human ovum with the abnormal 
embryo, showing the manner in which the villi arise by small roots, and also the 
process of multiplication of nuclei by gemmation. Magnified 465 diam. 
Fig. 2. — Various forms of the villi. Magnified about 6 diam. 
Fig. 3. — Formation of embryonic blood-vessels by the coalescence of cells, 
arising from the nuclei by budding. Magnified 465 diam. 
Figs. 4 and 5. — Embryonic blood-vessels in the course of development. Mag- 
nified 465 diam. 
Fig. 6. — Fragment of a villus from the chorion of a human embryo, about 16 
millimetres in length ; a, portion denuded of its epithelium, showing its fibrous 
structure with two capillary vessels in the process of formation ; 6, portion covered 
by the epithelium, which, out of focus in the middle, is only seen at the margin. 
Magnified 265 diam. 
Fig. 7. — Deeper layer of epithelial nuclei of the same villus, showing their 
multiplication by gemmation. Magnified 465 diam. 
Fig. 8. — Formation of blood-vessels by the fusion of spindle-shaped bodies in 
the pia mater of the spinal marrow of a human embryo about twelve weeks old. 
Magnified 465 diam. 
Fig. 9. — Blood-vessels of the pia mater from another embryo of the same age. 
The granular fibrillous bundles, of which the larger vessels were originally com- 
posed, are still distinguished. Magnified 465 diam. 
i Fig. 10. — Artery from the pia mater of the spinal marrow of a human embryo 
about nine to ten weeks old, showing three coats of the vessel. The interior is 
J) filled with blood-corpuscles, the greater portion of which became discoloured by 
J the action of the chromic acid solution, in which it had been laying ; the rest, 
3 comprising the younger ones, remained unaffected. Magnified 465 diam. 
Fig. 11. — Vein from the same preparation. Among the blood-corpuscles a 
VOL. XIII. B 
