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Endolymphatic Ducts in Crocodiles & Birds

Evolutionists try to predict where birds came from. One theory is that birds come from crocodiles because they both have an endolymphatic duct, which indicates that this structure was passed from the crocodile to the bird . Crocodiles are reptiles that are known for having unusually adept hearing, while birds use tubes to handle the complex process of flying.

Function
- The endolymphatic duct is located between the saccule ̵1; a bunch of sensory cells in the inner ear ̵1; and the utricle ̵1; a part of the inner ear. The duct ends in an endolymphatic sac, which controls fluid pressures and gets rid of waste materials. The endolymphatic duct contains viscous fluid, called the endolymph. The liquid contains much potassium, which is used to carry electrical currents in the hair cells. The fluid is highly positively charged because of amino acids in the fluid.
Inner Ear
- The endolymphatic tube is in the inner ear structure of the membranous labyrinth. It has both an extraosseous and intraosseous component. Extraosseous components are ones occurring outside the bone, while intraosseous components are within the bone. In birds, the two main chambers of the membranous labyrinth are the utriculus and the sacculus. The sacculus is the main hearing organ in fish, but is of lesser importance for other vertebrae, although it is in all them. This part of the ear is often used for balance.
Bird Characteristics
- The inner ears of the bird are a complex series of tubes of which the endolymphatic duct is only a part. The general area contains the sensory organ responsible for allowing the bird to hear: the cochlear labyrinth. The mechanoreceptors let the bird brain know about the position and movement of the head and are responsible for initiating the reflexes of the rest of the body, a useful feature when flying. In birds, the endolymphatic duct is in a bony labyrinth, though a plasma-like fluid called the perilymph separates the bone from the series of tubes.
Crocodile Characteristics
- In the crocodile, the duct comes from the sacculus, travels between the dura and the bony skull wall and forms into a sac shaped like a pear. The dura is the part of the crocodile that covers the brain. The sac expands into the upper part of the medulla. The endolymphatic sac is a flattened and cerebral part of the organ, closely integrated with the brain. The fact that the sac extends into the brain of the crocodile may be part of why the crocodile is capable of hearing so well.

Animals & Science