Page 36 - Adams and Stashak's Lameness in Horses, 7th Edition

2 Chapter 1

Caudal
VetBooks.ir Dorsal Caudal

Dorsal Cranial

Dorsal

Rostral

Ventral

Proximal

Ventral
Cranial
Caudal Cranial

Dorsal Dorsal
Palmar Plantar
Distal

Figure 1.1. Positional and directional terms.

provides sensation, vascular supply, and attachment for nerve endings from nerves in the corium penetrate
the overlying stratified squamous epithelium that consti­ between cells of the deepest layer of the epidermis.
tutes the hoof or ungual epidermis (L. ungula, hoof). Three histological layers comprise the hoof wall: the
Regions of the corium are named according to the parts stratum externum, stratum medium, and stratum inter­
of the hoof under which they are located: perioplic num (Figure 1.5). The superficial stratum externum,
corium, coronary corium, laminar corium, corium of the commonly called the periople, is a thin layer of horn
frog (cuneate corium), and solar corium. Histologically, extending distad from the coronet a variable distance;
coronary corium gives rise to elongated, distally directed this thin, soft layer wears from the surface of the hoof
papillae. Laminar corium forms a series of sheets that wall so that it is present only on the bulbs of the heels
interdigitate with epidermal laminae of the stratum and the proximal parts of the hoof wall. The bulk of the
internum of the hoof wall. Shorter papillae extend from wall is the stratum medium consisting of cornified horn.
2
the perioplic, solar, and cuneate coria. The stratum internum comprises the epidermal laminae.
In the coronary region, the deepest layer (the stratum Distal to the coronary sulcus (Figure 1.4), about 600
basale) of the ungual epidermis is a single layer of pro­ primary epidermal laminae of the stratum internum
liferating keratinocytes lying upon and between long interleave with the primary dermal laminae of the lami­
dermal papillae. Cellular division here pushes cells dis­ nar corium (Figures 1.6 and 1.7). Approximately 100
tad into the stratum medium of the hoof wall, forming microscopic secondary laminae branch at an angle from
2
the epidermis that undergoes cornification. Nearly the each primary lamina, further binding the hoof and
entire hoof is composed of a thick layer of anucleate corium together (Figures 1.3–1.6). The epidermal lami­
squamous keratinocytes. nae are routinely referred to as “insensitive,” whereas
For the most part, the keratinaceous tissues of the the dermal laminae are called “sensitive.” In the strictest
hoof are devoid of nerve endings; as a consequence it is sense, though, only the keratinized parts of the primary
the “insensitive” part of the foot. However, a few sensory epidermal laminae are insensitive; the deepest layer of