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March 16, 2012

Gray Cat's shed cornified claw sheath

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Above and below,

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one of the treasures she leaves around the house on a regular basis.

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What an amazing, fascinating creature she is.

For those of you who'd prefer more time away from what you're supposed to be doing: Your ship just came in.

Below, the abstract of a 2009 Journal of Anatomy paper investigating the structure of the cat claw sheath.

The structure of the cornified claw sheath in the domesticated cat (Felis catus): implications for the claw-shedding mechanism and the evolution of cornified digital end organs.

The morphology of cornified structures is notoriously difficult to analyse because of the extreme range of hardness of their component tissues. Hence, a correlative approach using light microscopy, scanning electron microscopy, three-dimensional reconstructions based on x-ray computed tomography data, and graphic modeling was applied to study the morphology of the cornified claw sheath of the domesticated cat as a model for cornified digital end organs. The highly complex architecture of the cornified claw sheath is generated by the living epidermis that is supported by the dermis and distal phalanx. The latter is characterized by an ossified unguicular hood, which overhangs the bony articular base and unguicular process of the distal phalanx and creates an unguicular recess. The dermis covers the complex surface of the bony distal phalanx but also creates special structures, such as a dorsal dermal papilla that points distally and a curved ledge on the medial and lateral sides of the unguicular process. The hard-cornified external coronary horn and proximal cone horn form the root of the cornified claw sheath within the unguicular recess, which is deeper on the dorsal side than on the medial and lateral sides. As a consequence, their rate of horn production is greater dorsally, which contributes to the overall palmo-apical curvature of the cornified claw sheath. The external coronary and proximal cone horn is worn down through normal use as it is pushed apically. The hard-cornified apical cone horn is generated by the living epidermis enveloping the base and free part of the dorsal dermal papilla. It forms nested horn cones that eventually form the core of the hardened tip of the cornified claw. The sides of the cornified claw sheath are formed by the newly described hard-cornified blade horn, which originates from the living epidermis located on the slanted face of the curved ledge. As the blade horn is moved apically, it entrains and integrates the hard-cornified parietal horn on its internal side. It is covered by the external coronary and proximal cone horn on its external side. The soft-cornified terminal horn extends distally from the parietal horn and covers the dermal claw bed at the tip of the uniguicular process, thereby filling the space created by the converging apical cone and blade horn. The soft-cornified sole horn fills the space between the cutting edges of blade horn on the palmar side of the cornified claw sheath. The superficial soft-cornified perioplic horn is produced on the internal side of the unguicular pleat, which surrounds the root of the cornified claw sheath. The shedding of apical horn caps is made possible by the appearance of microcracks in the superficial layers of the external coronary and proximal cone horn in the course of deformations of the cornified claw sheath, which is subjected to tensile forces during climbing or prey catching. These microcracks propagate tangentially through the coronary horn and do not injure the underlying living epidermal and dermal tissues. This built-in shedding mechanism maintains sharp claw tips and ensures the freeing of the claws from the substrate.

March 16, 2012 at 02:01 PM | Permalink


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Comments

fascinating research - would look great on a resume

Posted by: sherlock | Mar 17, 2012 4:08:10 AM

Hey, Jake - if the vibrasse are varigated in color, they make excellent bodies for Catskill flies.

Posted by: 6.02*10^23 | Mar 17, 2012 3:15:57 AM

I wonder if the Scarecrow in "The Wizard of Oz" understood
that paragraph after he received his diploma?

Because he had trouble with his first utterance,

"the sum of the square roots of any two sides of an isosceles
triangle is equal to the square root of the remaining side" (not true).

http://wiki.answers.com/Q/What_math_term_did_the_Scarecrow_say_when_he_got_the_diploma

Posted by: JoePeach | Mar 16, 2012 6:44:45 PM

Joe,

Whiskers are cooler to collect... ;-)

Jake

Posted by: Uncle Jake | Mar 16, 2012 4:42:10 PM

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