Budras_Анатомия лошади

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6. The Hoof (Ungula)

Cursorial specialization for speed—the hallmark of horses—has lengthened the horse´s limbs during phylogeny and has raised the animal on the tip of only a single digit (and hoof) on each of its limbs. Compared to the weight of horse, the ground surface of al hoof is exceedingly small. In addition to transmitting and cushioning this weight, the hoof must protect the underlying soft tissues: two reasons for the complexity of this structure, which in some parts of the world is referred to as the digital “organ”.

1a) DEFINITION OF THE HOOF: The hoof, in a narrow sense, is nothing more than modified skin covering the tip of a digit. In a wider sense, the hoof includes also the structures it encloses and protects, such as the distal phalanx (coffin bone), hoof cartilages, distal interphalangeal (coffin) joint, distal sesamoid (navicular) bone, tendons, ligaments, blood vessels, and nerves. (This in the jargon of horse owners, is known as “the foot of the horse”, although it bears, no resem-

blance to the human foot, for instance.) The remarkable skin modification that has taken place involves the three layers of the skin:

2; 3 epidermis, dermis, and subcutis, but not uniformly in all parts of the hoof. Characteristic for the hoof is, that it has no hair, no sebaceous and sweat glands (except for some associated with the frog), and that it has a firm outer epidermis that must be trimmed (like a fingernail) it its wear with the ground des not keep pace with its growth; or conversely, it needs metal shoes if its growth does not keep pace with wear on man-made surfaces.

4For its study the hoof is best macerated. This grossly separates the hard hoof epidermis from the underlying dermis by destroying the soft basal and spinous layers, but leaving the stratum corneum (the actual hoof capsule) intact. The two upper left Figures on the opposite page illustrate that the interior of the hoof capsule can be likened to the (negative) imprint of the (positive) dermis-covered foot from which the capsule was removed.

The hoof capsule* consists of wall, sole, frog and bulb. The wall (10, 11) is the part visible in the standing horse. It comprises a toe in front, quarters on the sides, and medial and lateral heels (30) at the back, where the wall reflects on itself to form medial and lateral bars (24, 25) that flank the frog from which they are separated by paracuneal groves (29). The sole (22, 23) fills the space between the wall and frog; its parts between quarters and bars are its angles. The triangular frog (27, 28) projects into the sole from behind and closes the gap between the heels. Its two curar at the back of the hoof, thicken, spread upwards, an overhang the heels as the bulbs of the heels (26). The bulbs of the heels together with the frog are the homologue of the digital pad.

5The dermis of the hoof bears papillae (1, 2, 4, 5) which in the large wall segment (see further on) are represented by dermal Lamellae

(3). The mitotically active cells in the basal and spinous layer of the hoof epidermis—the ones that maceration destroyed—produce the horn (stratum corneum) of the hoof by passing through processes of keratinisation and cornification until they die as mature horn cells. The epidermis overlying to consist of horn tubules embedded in intertubular horn. The same cells overlying the dermal lamellae produce epidermal lamellae which interdigitate with their dermal neighbors and make possible the movement of the wall toward the ground.

6b) For further description the hoof may be divided into FIVE SEG- MENTS which are most easily recognized in the upper left drawing on the opposite page. The horn produced in the first three segments forms the wall of the hoof. The respective skin modifications will be described for each segment.

I. The arrow perioplic segment (Limbus) circles the hoof adjacent to the haired skin. It widens on the palmar/plantar aspect of the hoof where it merges with the fifth (frog/Bulb) segment. (The junction between skin and periople is known as the Coronet.) The perioplic dermis (1) has short dermal papillae, which increase in length distally. These are covered by 1the periople (epidermis limbi —9)

Clinical and Functional Anatomy p. 135–138

which is unpigmented, soft horn and appears whitish on the intact hoof. It descends as the external layer of the hoof wall but fails to reach the ground because it dries and gets worn away. The subcutis underlying the perioplic dermis is a slightly thickened ring known as the perioplic cusion (33).

II. The wider coronary segment (Corona) follows the perioplic segment distally and is separated from it by a shallow grove. The coronary dermis (2) is studded with papillae which are longest distally where they can be made out with the naked eye. The coronary epidermis (10) forms the diddle layer of the hoof wall. This horn is hard, pigmented horses, and is pushed toward the ground by the growth of its living basal and spinous layers covering the coronary dermis. The coronary horn consists of many horn tubules (17) which can be detected on the surface of the wall as proximodistally directed fine lines. The subcutis is present in the form of a ringlike coronary cushion (34) that causes the overlying coronary dermis to bulge and allows its papillae to be directed toward the ground.

III. The wall segment (Paries) lies deep of the hoof wall and extends from the coronary segment to the ground. The parietal dermis (3, 3') lies directly on the distal phalanx (39) and on the external surface of the hoof cartilages. The parietal dermis consists of primary and secondary dermal lamellae present only in this segment. The crests of the dermal lamellae give rise, near their proximal and distal ends, to small cap papillae which are directed distally. Similarly, the distal ends of the dermal lamellae bear a short row of terminal papillae (3') that also continue in the direction of the lamellae toward the ground. The living epidermal cells on the dermal lamellae produce epidermal lamellae (11) which interdigitate with the dermal lamellae; their centers are cornified (horny lamellae —19) and it is these that are visible on the internal surface of the wall of the hoof capsule. The living epidermal cells of the wall segment by their continuous mitotic activity make possible the slow, distal migration of the hoof wall. The horn produced over the capand terminal papillae presents horn tubules that are better developed and visible only in the terminal horn near the ground where they can be

made out in the white line (zona alba —18, —20) as faint dots 7 between the horny lamellae.

The horn produced over the parietal dermis is covered by, and is 8 continuous with, the thick plate of horn produced over the coronary dermis and becomes visible only at the white line of the intact hoof. The width of the white line is taken into consideration in the diagnosis of hoof diseases, for example in laminitis. The subcutis is absent in the wall segment.

Dermis and epidermis of the wall segment transfer part of the weight upon the limb to the inside of the wall through the following structures: distal phalanx, to the dermal lamellae, by interdigitation to the horny lamellae of the wall, and through the sole border of the wall to the ground.

IV. The slightly concave sole segment (Solea) occupies the space between the sole border of the wall and the grog/bulb segment. The dermis of the sole (4) lies directly on the sole surface of the distal phalanx and presents short dermal papillae. The horn of the sole is hard tubular horn. A subcutis is absent.

V. The frog/bulb segment forms part of the groundand the pal- 9 mar/plantar surface of the hoof. The dermis of the frog/bulb segment (8, 5) presents papillae which spiral in the bulbar part while being straight where they underlie the frog. The horn produced by

the overlying epidermis (13, 16) has spiralling horn tubules and is soft in the bulbar part of the segment and in the center of the frog; close to the sole the horn of the frog ist hard. the subcutis deep to the frog is a thick wedge that occupies the spache between the deep flexor tendon and the hoof cartilages; it is al feltwork of fibrous connectiveand adipose tussue known as the digital cushion (35, 36).

Hoof

Hoof dermis

(Proximolateral view)

1Perioplic dermis

2Coronary dermis

3 Parietal dermis (dermal lamellae)

3'Terminal papillae

Hoof capsule

(Distolateral view)

Wall

9 External layer (Periople)

10 Middle layer (Coronary horn)

11Internal

layer (Parietal

horn)

33 Perioplic cushion

34 Coronary cushion 35, 36 Digital cushion 37 Proximal phalanx 38 Middle phalanx

39 Distal phalanx

40 Navicular bone

41 Common digital extensor tenden

42 Deep digital flexor tendon

43 Glands of the frog

Torus metacarpeus

Median section

6Dermis of the bars (Coronary part)

7Dermis of the bars

8Dermis of the bulb of the heel

3'''

3'

11'

Distal interphalangeal (coffin) joint

14 Bar (Parietal part)

15 Bar (Coronary part)

16 Bulb of heel

Ground surface

43

8

16

7. Suspensory Apparatus of the Coffin Bone

Clinical and Functional Anatomy p. 138–141

The horse is an animal walking on the border of the tip of the toe. That means that its body weight rests predominantly on the solear border (margo solearis —5) of the hoof; whereas, its modified digital pad, the sole (solea ungulae) and the frog (cuneus ungulae) of the hoof, depending on the character of the ground-surface, bear only a small part of the body weight. This is in contrast to the claw (see Atlas of

Bovine Anatomy). Within the hoof, the body weight of a horse is transferred from the coffin bone (os ungulare) to the hoof plate by the

1suspensory apparatus of the coffin bone (apparatus suspensorius ossis ungulae) and by this to the solear border of this hoof plate.

I. DEFINITION OF THE SUSPENSORY APPARATUS OF THE COFFIN BONE.

The suspensory apparatus of the coffin bone is a constituent of the equine hoof. The concept, suspensory apparatus of the coffin bone, comprises all connective tissue and epithelial structures in the wall segment as a functional unit of the hoof, which transfers the body weight. The body weight rests as a pressure-force on the coffin bone

(os ungulare —3) and is transferred as a tensile force onto the hoof plate. The wall corium (dermis parietis —2) and the wall epidermis

(epidermis parietis —1) are part of this suspensory apparatus.

a) The wall corium is a taut, collagen-fibered connective tissue, conducting blood vessels and nerves. The collagen fiber-bundles originate at the parietal surface of the coffin bone. Proximodistally running bony crests are characteristic for the parietal surface of the coffin bone, at which —and less between them— the collagen fiberbundles of the wall dermis arise directly in the bone tissue by way of a chondroapophyseal insertion. The coffin bone has no periosteum in this insertional zone of the connective tissue part of the suspensory apparatus of the coffin bone. Moreover, partially calcified fibrocartilage is embedded here. The collagen fiber-bundles of the wall corium exchange fibers with each other, and by this a dense network of fibers, the reticular layer (2”) (stratum reticulare) of the wall corium is formed. The collagen fiber-bundles then run radially, obliquely distoproximally in direction into the primary and secondary dermal lamellae (stratum lamellatum dermidis parietis —

2') and insert on the basal membrane that joins the parietal dermis and parietal epidermis together.

b) The parietal epidermis with its primary and secondary laminae is interlocked with those of the dermis. With the putting down

(weight-bearing) of the hoof, the tensile force acting on the secondary lamellae is transferred via the basal membrane onto the basal and spinous cells in the secondary epidermal lamellae. These are connected via hemidesmosomes on the basal membrane or via desmosomes to each other and via finger-like processes to horn cells within the primary epidermal lamellae. These primary epidermal lamellae or horny lamellae pass over continuously into the intertubular horn of the coronary horn and wind around the coronary horn tubules in a basket-like manner. By these intensive connections in the form of intercellular junctions and interdigitating cell processes, the tensile force is finally transferred to the coronary horn in the epidermal part of the suspensory apparatus of the cof-

2fin bone. This then rests as a pressure force on the solear border of the hoof plate.

II. The vessels that supply the hoof originate from the lateral and medial plantar (palmar) digital arteries (6) and veins. Functionalanatomically it should be noted that the lateral and medial digital arteries are multiply connected with each other by their branches

(coronal artery [a. coronalis —7], dorsal branch of the distal phalanx [r. dorsalis phalangis distalis —9], terminal arch [arcus terminalis —13]), by which the blood supply is assured in variable loading of the hoof. In the same manner the lateral and medial veins are connected with each other, especially with their venous plexuses (plexus ungularis —11) that lie axial and abaxial to the ungular cartilage (cartilago ungulae —4). These venous plexuses, working together with the hoof mechanism, have a special importance for the drainage from the hoof. The superficial and deep arteriovenous anastomoses, which are described in the haired skin, lie in the corium of the hoof at the base of the dermal papillae or, respectively, at the base of a primary dermal lamella. It is by these that the blood can be drained in the papillary body of the modified ungular skin with by-passing of the terminal network of subepidermal capillaries.

The medial and lateral plantar (palmar) digital arteries (6) extend distally in the company of the same named veins and nerves on the sides of the deep flexor tendon. The artery of the digital cushion

(ramus tori ungulae 12) branches from the plantar (palmar) digital

28

artery at the level of the proximal border of the ungular cartilage. It gives off a branch peripherally into the bulb of the heel and an axial branch to the crus of the frog. The coronal artery (7) arises from the abaxial wall of the plantar digital artery closely above the proximal border of the hoof capsule. It gives off dorsal branches and branches for the quarter region. Shortly before the plantar (palmar) digital artery enters the axial solear foramen or, respectively, the abaxial solear foramen there arises from its abaxial side a short common trunk for the artery of the hoof wall (ramus dorsalis phalangis distalis —9) and the artery of the coffin bone (ramus plantaris phalangis distalis —9'). These two arteries run on the surface of the bone and each gives off proximal as well as distal branches. The proximal branches of the ramus dorsalis phalangis distalis are connected to the distal branches of the coronal artery. Arterio-arterial anastomoses are also found at the distal border of the coffin bone and its plantar

(palmar) processes. Here, the distal branches of the ramus dorsalis phalangis distalis and ramus plantaris (palmaris) phalangis distalis are connected with each other arcade-like to form the artery of the solear border (a. marginis solearis —10), which again anastomoses with distal branches of the ramus tori ungulae and those of the terminal arch (arcus terminalis) of the plantar (palmar) digital arteries.

The terminal arch is the terminal part of the anastomosing lateral and medial plantar digital arteries and veins in the semicircular bony canal of the coffin bone (see text-figure, 13). The arterial pulse wave is transferred to the accompanying veins, by which the blood drainage from the hoof is enhanced.

Dorsal view

6

10

13

3

6

The subcutaneous arteries form a network from which the dermal vessels (rete dermale parietale —8) proceed. These ramify within the dermis just below the surface of the papillary body in a subepidermal capillary vascular plexus, from which originate the draining venules and veins. These veins again form a superficial, dermal, and deep, subcutaneous, (excluding the wall and sole segment) vascular plexus, from which the draining veins originate at the coronary and solear borders of the hoof. The venous drainage from the hoof in the subcutaneous venous plexus that lies axial and abaxial to the ungular cartilages is facilitated by the hoof mechanism in placing the foot down (weight-bearing) and lifting it up (pressure-suction pump).

III. The nerves of the hoof originate from the lateral and medial plantar (palmar) digital nerves (6). The latter nerves run lateral or, respectively, medial to the deep flexor tendon distally to the hoof and accompany the same-named arteries deep to the ligament of the ergot to the axial aspect of the ungular cartilage. Proximoplantar (-palmar) to the ungular cartilage a branch of the digital cushion (ramus tori ungulae) branches off from the digital nerve of each side. The continuing digital nerve turns dorsodistally axial to the plantar (palmar) process of the coffin bone, gives off branches for the coffin joint axially and enters the solear foramen to reach the solear canal of the coffin bone. In its semicircular course through the solear canal, proximal and distal nerve branches are given off. These together with arteries and veins penetrate the bone in a radiating manner. On the parietal surface of the coffin bone they enter the parietal dermis proximally and distally. Here again they branch into proximal and distal branches. These branches form a deep dermal network. From the branches of the deep dermal network, nerves branch off at the base of a lamella. Nerve end-corpuscles (tactile corpuscles) lie predominantly in the subcutis of the frog and heel. They appear moreover in the subcutaneous cushion of the periople and coronary dermis.

2

3

Median section

Suspensory apparatus of the coffin bone

Arrows:

Pressure Tension Pressure Axis of rotation

Curved arrows: Coffin bone rotation

Plantar process of the distal phalanx

Dermis of the sole Sole (angle)

Frog

5 Solear border

Central sulcus of the frog

Crus of the frog

Deep digital flexor tendon

Paracuneal sulcus

Bar (pars inflexa)

6 Medial and lateral digital artery, vein, and nerve

(Dorsolateral view)

Coronary branch of the digital nerve

Digital extensor tendon

7Coronary artery and vein Accessory cartilage

8Dermal vessels

9 Artery of the

hoof wall

9' Artery of the

coffin bone

12 Branch of the digital cushion

4 11 Venous plexus

10 Artery and vein of the solear border

1

2

3

aGastrocnemius

bMedial digital flexor

cSuperficial digital flexor

dTibialis caudalis

eLateral digital flexor

fTibialis cranialis

gPeroneus tertius

hLong digital extensor

iLateral digital extensor

(Craniolateral view)

Stifle joint

(Lateral view)

Hip joint

Subcutaneous calcanean bursa Subtendinous calcanean bursa

Chapter 4: Head

1. Skull and Dentition

a)The SURFACE FEATURES of the skull such as processes, crests, and notches are helpful landmarks during palpation, while deeper skeletal features serve the same purpose when examining radiographs. The orbit lies between the facial and cranial parts of the skull and

1has a complete bony rim, since the zygomatic process of the frontal bone (1) is long enough to reach the zyomatic arch. The tympanic bulla (17) is unobtrusive and situated medial to the styloid process (10') of the temporal bone. The distinct external occipital protuberance (31) for the attachment of the nuchal ligament lies in the midline half way between the nuchal crest (m) and the foramen magnum (38). The lateral surface of the skull' s facial part is characterized by the facial crest (57') that extends from the maxilla to the zygomatic arch. Between the nasal process (69) of the incisive bone and the nasal bone is the nasoincisive notch (X.”), an easily palpated landmark. Midway between the rostral end of the facial crest and the nasoincisive notch lies the palpable infraorbital foramen (59) which is a landmark for a nerve block.

b)The more deeply situated FORMINA may be used for orientation on radiographs, and certain others are occasionally used to block nerves emerging from them.

A prominent foramen is the foramen lacerum (45') on the base of the skull between sphenoid, temporal, and occipital bones. Its rostral portion is sculpted to present an oval notch (45) and an carotid notch (p') which are separate foramina in the dog, for example. The caudal part of the foramen lacerum narrows to form the jugular foramen (q). The roof of the cranium presents a series of dorsal apertures (h') for veins which connect with the temporal meatus. The supraorbital foramen (1') transmits the frontal nerve that arises in the orbit.

The notch for the facial vessels on the ventral border of the mandible is an important landmark in the horse for taking the pulse (see p. 35.77').

c) The DENTITION OF THE HORSE is characterized by almost all teeth being hypsodont (they are tall and continue to grow in length after erupting), by a molarization of the premolars to form a continuous grinding surface with the molars, and by the two rows of lower cheek teeth standing closer together than the two rows of cheek teeth in the upper jaw. Distinct lateral masticatory movements cause the cheek teeth to obtain a flat, though very rough, occlusal surface. The horse, as the other domestic mammals, has a heterogeneous dentition that consists of incisors (I), canines (C), premolars

(P), and molars (M) of which the two last-named are similar and because of this are referred to simply as cheek teeth.

The dental formula for the deciduous teeth is

A further characteristic of the equine dentition is that the canine teeth are fully developed only in the male, and that the first premolar (P1) is a vestige (“wolf” tooth) that not always erupts. These

Clinical and Functional Anatomy p. 145–147

two teeth are brachydont which means that they are fully formed when erupted and do not increase in length as do the remaining hypsodont teeth. The growth of the horse's hyposodont teeth ceases about seven years following eruption. At that time short roots form on the cheek teeth while the foramen at the proximal end of the incisors gets increasingly smaller. Such teeth have to last the horse until death. Deposition of cement and bone at the bottom of the tooth sockets now pushes the teeth out of the jaws; this proceeds at the rate of wear at the occlusal surface which for the cheek teeth is 2–3 mm per year. Another feature of the cheek teeth is the extreme folding of their enamel casing. There is also invagination of the enamel at the occlusal surface producing infundibula. Both the folding and the invagination results in multiple raised enamel ridges on the occlusal surface separated by the softer dentin. Combining these features with the horizontal chewing movements of the mandible makes for a very efficient grinding mechanism. The enamel of the incisors is also invaginated at the occlusal surface (forming one infundibulum) resulting in two raised enamel rings when the tooth is in wear. Cement surrounds the enamel casing of both types of teeth while dentin fills the space between the enamel and the dental cavity within the tooth.

The surfaces of the teeth are known as mesial (facing the median plane along the dental arch), distal (the opposite surface), vestibular, and lingual; and the occlusal or working surface. The usual division of a (brachydont = short) tooth into crown, neck (at the gum line), and root (in the socket and clothed by cement) is not applicable to the horse's teeth. The reason is the growth at the proximal end of the teeth and their continuous extrusion from the jaw. Therefore, the part showing in the mouth may be called clinical crown, and the hidden, much longer portion, the body of the tooth.

Secondary dentin

Enamel fold

Raised enamel ridge

Cement

Enamel

Dentin

Secondary dentin

M1 Dental cavity

Foramen at tip of root

I2

Cup

Cement filling bottom of infundibulum

Invaginated enamel forming infundibulum

Dental cavity

Foramen at proximal end of tooth

Cranium

External lamina (a) Diploe (b)

Internal lamina (c)

Osseous tentorium cerebelli (d) Temporal meatus (e)

Canal for transverse sinus (f)

Groove for transverse sinus (g) (not shown) Retroarticular foramen (h) ●

Dorsal apertures (h') Temporal fossa (j)

External frontal crest (k) External sagittal crest (l) Nuchal crest (m) Temporal crest (m') Carotid notch (p')

Jugular foramen (q) Petrooccipital fissure (q')

Neurocranial bones

I. Frontal bone

Zygomatic process (1) ●

Supraorbital foramen (1')

Ethmoidal foramina (2)

IV. Temporal bone ●

a.Petrosal part (6) Mastoid process (7) Internal acoustic meatus

Internal acoustic orifice (8)

Facial canal (9)

Stylomastoid foramen (10) Styloid process (10')

Petrotympanic fissure (12) Cerebellar [floccular] fossa (13) Canal for trigeminal nerve (14)

b.Tympanic part (15)

External acoustic meatus External acoustic orifice (16)

Tympanic bulla (17) ●

Tympanic opening of auditory tube (17') ● Muscular process (17'')

c.Squamous part (18)

Zygomatic process (19)

Mandibular fossa (20) ●

Articular surface (21) ●

Retroarticular process (22) ●

VI. Occipital bone ●

Squamous part (30) ●

External occipital protuberance (31) ● Tentorial process (31')

Lateral part (32) ● Occipital condyle (33) ●

Canal for hypoglossal nerve (35) ● Paracondylar process (36) ●

Basilar part (37) ● Foramen magnum (38) ● Muscular tubercle (49) ●

VII. Sphenoid bone ●

Basisphenoid

Body (41) ●

Sella turcica (42) Wing (43) ●

Foramen rotundum (44) Oval notch (45) Foramen lacerum (45') ● Pterygoid crest (46)

Alar canal (47) ●

Rostral alar foramen (48) Small alar foramen (48') Caudal alar foramen (49) ●

Prephenoid

Body (50) ●

Wing (51) ●

Optic canal (52)

Orbital fissure (53)

Face

Pterygopalatine fossa (A) ● Major palatine canal ●

Caudal palatine foramen (B) ● Major palatine foramen (C) ●

Minor palatine canals ●

Caudal palatine foramen (B) ● Minor palatine foramina (D) ●

Sphenopalatine foramen (E) ● Choanae (F) ●

Orbit (G) ● Palatine fissure (H) ● Dental alveoli (J)

Alveolar rigdes (K) ● Alveolar canals (L) Interalveolar septa (M) Diastema (N)

Facial bones

VIII. Lacrimal bone ●

Fossa for lacrimal sac (54)

IX. Zygomatic bone ●

Temporal process (55)