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The urachus forms from the distal end of the allantois in the embryo, and develops into a closed cord between the base of the bladder, and the navel. [1] It drains the bladder of the fetus that joins and runs within the umbilical cord . [ 2 ]
Diagrams to show the development of male and female generative organs from a common type. A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. 3. Ureter. 4. Urinary bladder. 5. Urachus. cl. Cloaca. cp. Elevation which becomes clitoris or penis. i. Lower part of the intestine. ls.
Diagrams to show the development of male and female generative organs from a common type. A.—Diagram of the primitive urogenital organs in the embryo previous to sexual distinction. 3. Ureter. 4. Urinary bladder. 5. Urachus. cl. Cloaca. cp. Elevation which becomes clitoris or penis. i. Lower part of the intestine. ls.
Dogs have ear mobility that allows them to rapidly pinpoint the exact location of a sound. Eighteen or more muscles can tilt, rotate, raise, or lower a dog's ear. A dog can identify a sound's location much faster than a human can, as well as hear sounds at four times the distance. [41] Dogs can lose their hearing from age or an ear infection. [42]
The fetal membranes separate maternal tissue from fetal tissue at a basic mechanical level. The fetal membrane is composed of a thick cellular chorion covering a thin amnion composed of dense collagen fibrils. The amnion is in contact with the amniotic fluid and ensures structural integrity of the sac due to its mechanical strength.
During fetal development, the allantois becomes the urachus, a duct between the bladder and the yolk sac. A patent allantois can result in a urachal cyst. Because the allantois can be cultured ex vivo, it has utility as a model system for studying the formation of blood vessels as well as considerable usefulness in drug screening.
The urogenital sinus divides into three parts, with the upper and largest part becoming the bladder; the middle part becoming the urethra, and the lower part changes depending on the biological sex of the embryo. [17] The human bladder derives from the urogenital sinus, and it is initially continuous with the allantois.
Virgin dogs can become quite distressed at finding themselves unable to separate during their first copulation, and may try to pull away or run. Dog breeders often suggest it is appropriate for handlers to attempt to calm the mating dogs if they show anxiety once this stage is reached. After mating, the male usually licks his penis and prepuce.