Editing Bladder (section)

=== Mammals ===
{{Multiple image
| image1            = The anatomy of the domestic animals (1914) (20553749470).jpg
| image2            = The anatomy of the domestic animals (1914) (18009226539).jpg
| footer            = Bladder, prostate, and seminal vesicles of a [[stallion]]
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All species of mammal have a urinary bladder.<ref>{{Cite book |last1=Flower |first1=William Henry |url=https://books.google.com/books?id=YclRAAAAMAAJ&dq=bladder&pg=PA69 |title=An Introduction to the Study of Mammals Living and Extinct |last2=Lydekker |first2=Richard |date=1891 |publisher=A. and C. Black |language=en}}</ref> This structure begins as an [[embryonic cloaca]]. In the vast majority of species, it eventually becomes differentiated into a dorsal part, connected to the intestine, and a ventral part, associated with the urinogenital passage and urinary bladder. The only mammals in which this does not take place are the [[platypus]] and the [[Echidna|spiny anteater]], both of which retain the cloaca into adulthood.<ref name="ABC">{{cite book|url=https://archive.org/stream/chordates00rand/#page/276/mode/1up/search/bladder|title=The Chordates|date=1950|publisher=Balkiston|author=Herbert W. Rand}}</ref>

The mammalian bladder is an organ that regularly stores a hyperosmotic concentration of urine. It therefore is relatively impermeable and has a multi-layer epithelium. The urinary bladders of [[cetacean]]s (whales and dolphins) are proportionally smaller than those of land-dwelling mammals.<ref name="Hunter2015">{{cite book|url=https://books.google.com/books?id=TNAIBwAAQBAJ&pg=PR35|title=The Works of John Hunter, F.R.S.|date=26 March 2015|publisher=Cambridge University|isbn=978-1-108-07960-0|page=35|author=John Hunter}}</ref>