A text-book of animal physiology : with introductory chapters on general biology and a full treatment of reproduction, for students of human and comparative (veterinary) medicine and of general biology / by Wesley Mills ... with over 500 illustrations.

T. Wesley Mills

Date:: 1889

Credit: A text-book of animal physiology : with introductory chapters on general biology and a full treatment of reproduction, for students of human and comparative (veterinary) medicine and of general biology / by Wesley Mills ... with over 500 illustrations. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

109/750 page 77

$and, being filled with fluid, the zona is thinned and soon disap- pears. The germinal area alone is made up of three layers of cells (Fig. 104), the rest of the upper part of the oosperm being lined ■with epiblast and hypoblast, while the lower zone of the yelk- sac consists of epiblast only. Simple, non-vascular villi, serving to attach the embryo to the uterine walls, usually project from the epiblast of the subzonal membrane. In the rabbit they do not occur every- where, but only in that region of the epiblast beneath which the mesoblast does not extend, with the exception of a patch which soon appears and demarkates the site of the future placenta. The extension of the mesoblast takes place in every direction from the embryo except directly around the head; but the two Fig. 85.—Diagrammatic median vertical longiturlinal section.s through embryo ral)l)it (Had- don. after Van Bi-neden and Julin). A. Section through embryo of Fig. H4. \i. Section tlirough f nibryf) of eleven days, al, allautois ; arn, amnion ; a. ins, anterior median plate of mi'soblast, formed by the junction of the anterior horns of the area opaca ; ti. pt, area placentalis ; a. r. area vasculosa ; ch, chorion ; cw, c(]Blom of embryo ; cw', extra-embry- onic portifin of the body-cavity ; eyj, epiblast; h;/, hypoblast; m. uusplit mesoblast ; o. «, oriflo- of amnion ; pi, |>lacenta ; jjrn, a, proamnion ; g. (, sinus terminalis ; v, epiblastic villi of blastodermic vesicle. expansions of the mesoblast which mark out this area extend for some di.stance in front of the head, and ultimately unite ; so that immediately in front of the head there is a circular region in wliich tlio Ijlastodei-m consists of epiblast and hypo-$