Page 361 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Common integument (integumentum commune) 343

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15.31 Longitudinal section of a claw (young dog). Haematoxylin and eosin stain (x32).

Adipose tissue within digital pad

Hairless, heavily keratinised epidermis

Dermal papilla

15.32 Digital pad (cat). Haematoxylin and eosin stain (x25).

The digital pad is characterised by a thickened, modi- the horny epidermis. In the epidermis, the keratinocytes
fied subcutis that is reinforced with strands of connective are transformed into predominantly tubular horn that
tissue fibres and encloses pockets of adipose tissue (Figure gives rise to the characteristic shape of the horn casing.
15.32). Eccrine sweat glands are present within the con- Intertubular horn is minimal in cattle and more deve-
nective tissue cushion. The epidermis is extensively loped in small ruminants. Fluctuation in the nutritional
keratinised. In the cat, it contains numerous pressure sen- supply of the basal cells of the stratum germinativum
sitive lamellar bodies. results in the formation of rings that manifest as irregu-
larities in the surface of the horn (e.g. during and after
Horn pregnancy and disease).
Like the digital organs, the horn of ruminants is a modifi-
cation of the external skin in which the layered structure Skin of birds
is largely preserved. The horn covers the hollow cone of The majority of the avian body is covered with feathers
bone (cornual process) projecting from the frontal bone of (pennae). Originating from the epidermis, these structures
the skull. The tough periosteum of the bone is continuous are a characteristic and unique feature of the class Aves.
with the thin subcutis of the horn. The papillated dermis The feather coat of birds performs many functions for
adheres tightly to the subcutis, forming the template for which hairy skin is responsible in mammals, including:

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