Top Contributors - Chelsea Mclene, Tarina van der Stockt, Jess Bell and also Kim Jackson
2 Axial Skeleton2.1 Skull3 Joints and also Ligaments3.2 Cervical Spine3.2.1 Joints3.3 Thoracic Spine (T1-T18)3.4 Costovertebral Joint3.5 Lumbar Spine3.5.1 Joints4 Myology and Neurology4.1 muscle of the Head4.1.2 Ear4.1.7 muscle of the Hyoid Apparatus and Larynx

Introduction

Equine anatomy refers to the gross and also microscopic anatomy of horses and also other equids (donkeys, and zebras).

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This web page introduces the Anatomy of equine Spine and also Head.


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Axial Skeleton

The axial skeleton is composed of the skull, vertebral column, sternum, and ribs. Lot of sternebrae fuse to form one bone, attached come the 8 "true" pairs of ribs, out of a full of 18.<1>

The vertebral column has 54 bones:

7 cervical vertebrae: has the atlas (C1) and axis (C2)18-19 thoracic vertebrae5-6 lumbar vertebrae5 sacral vertebrae

In details breeds, there may be variations in these numbers.<3>

Skull

The skull contains the brain and the most necessary organs that sense.

Cranium

The Roof that the cranium is made up of frontal and also parietal bones.

The Floor is made up of sphenoid bone.

The cranium is composed of 5 orbit regions:

FrontalLacrimalPalatineSphenoidZygomatic

Interparietal bone: only discovered in horse and cat.

The orbit is finish in horse and ruminants while the is incomplete in carnivores however completed through the orbit ligament.

The lacrimal fossa collection tears and also sends them through lacrimal canal right into the nasal cavity.

Bones in the steed Skull
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There are 34 bones and most that them room flat. During the birth process, these bones overlap and allow the skull to compress as much as feasible to allow for parturition.

The 14 major bones are:<1>

Incisive bone (premaxillary): component of the upper jaw; wherein the incisors attachNasal bone: consist of the nasal cavityMaxillary bone: a large bone that consists of the roots of the molarsMandible: lower section of the jaw; biggest bone in the skullLacrimal bone: contains the nasolacrimal duct, which carries fluid from the surface of the eye, to the noseFrontal bone: create the forehead of the horseParietal bone: extends native the forehead to the back of the skullOccipital bone: develops the joint in between the skull and the first vertebrae that the neck (the atlas)Temporal bone: includes the eternal acoustic meatus, which transmits sound from the ear come the cochlea (eardrum)Zygomatic bone: attaches come the temporal bone to form the zygomatic arch (cheekbone)Palatine bone: forms the back of the tough palateSphenoid: developed by blend of the foetal basisphenoid and presphenoid bones, in ~ the base of the skull. Deserve to become broken in horses that behind over backwardsVomer: forms the peak of the within of the nasal cavityPterygoid: small bone attached to the sphenoid that extends downwardCavities

The equine skull is composed of 4 cavities:

The cranial cavity: Protects and encloses the brain, supports feeling organs. The cranium is composed of a roof comprised of the frontal and parietal bones and also a floor consisted of of the sphenoid boneThe orbit cavity: has 5 orbits: frontal, lacrimal, palatine, sphenoid and also zygomatic. That protects and also surrounds the eye.<4> Horses have both monocular and binocular vision:Monocular vision: The horse deserve to see objects through one eye. This means that the mind receives two images simultaneouslyBinocular vision: The horse can focus with both eyes as with humans and also the brain receives only one signalThe oral cavity: A passage right into the respiratory and also digestive systemThe nasal cavity: has bone the protects the mucous membrane indigenous inspired warmth airForamina the the Skull and the structures Passing ThroughForaminaStructures pass through
Infra-orbital foramenInfra-orbital nerve. CNV
Maxillary foramen
Cribriform foramenOlfactory nerve. CNI
Optic canalOptic nerve. CNII
Orbital fissureCNVII, IV, V and also VI (ophthalmic division)
Round foramenCNV (maxillary division)
Oval foramenCNV (mandibular division)
Foramen lacerumInternal carotid artery

CN V3 (horse and also pig)

Internal acoustic meatusCNVIII
Jugular foramenCNIX, X, XI
Stylomastoid foramenCNVII
Mandibular foramenCNV (mandibular alveolar nerve)
Mental foramen

Joints and Ligaments

Joints and Ligaments of the Skull

Mandibular symphysisHyoid apparatus - consists of 3 joints:Tympanohyoid cartilage- skull (syndesmosis)Interhyoid joints (synovial)
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Atlanto-Occipital Joint

A condylar, modified synovial hinge joint. The articulating surfaces are the occipital condyles and also the cranial articular surfaces of the atlas (C1). There are three thickenings that strengthen the spacious joint capsule: Dorsal, Ventral, Lateral. The transverse atlantal ligament holds the dens that the axis versus the ventral arch that the atlas.<1>

Atlanto-Axial Joint

A pivot joint in between the atlas and also the saddle shaped surface ar of the axis (C2), i m sorry extends top top the dens. It has actually a loose joint capsule. The apical ligament that dens connects the apex of the dens to the occipital bone. Motion at this joint has rotation of the atlas and also head upon the axis and some accessory lateral flexion.<1> Rotation at this joint renders up 73 percent that cervical rotation.<6>

Cervical Spine C3-C4

A planar, extensive, oval shaped joint that is obliquely oriented in transverse plane. The cranial articular processes challenge dorsomedially and also the caudal articular processes face ventrolaterally. Spinous procedure height increases caudally from C6. Lateral flexion is the primary motion at this joints (25-45 degrees each share - C1/C2 only has actually 3.9 degrees of lateral flexion).<6>

LigamentsDorsal longitudinal ligamentVentral longitudinal ligamentLigamentum flavumNuchal ligament:This ligament connects the thoracic vertebra to the head and assists in supporting its weight. It is composed of 2 paired parts:<1>Funicular (cord) part - extends from the poll to +/- the second to the fourth thoracic spinous processLamellar component - occurs from the second and 3rd thoracic spinous processes and the funicular part, and inserts top top the C2-C6 spinous processes. The very first digitation going to the axis is really strong, yet it decreases in toughness caudally

Thoracic Spine (T1-T18)

Articular processes

Caudal articular processes challenge ventrally and also are positioned at the base of the spinous process. The cranial articular processes room oval facets ~ above the arch the the vertebra and face dorsally. Each thoracic vertebrae has a pair that costal facets ~ above the dorsal human body (except the last) forming the costal fovea.<1>

Anticlinal vertebrae: This is the suggest in the caudal thoracic vertebral obelisk at i m sorry the anatomic attributes of the vertebra begin to change.<7> This normally occurs in ~ the 13th vertebra in horses.

Motion:

Flexion - many flexion occurs at T17/T18; least flexion wake up at T3-T9Rib Neck

Has 2 converse facets: Cranial and Caudal

Rib 1 attaches come C7, T1 and the linked IV disc

Motion: rotation that the rib, i beg your pardon is greater caudally

Costovertebral Joint

Joints

The costovertebral joints have actually two unique articulations in between most ribs and also the vertebral column:<1>

Head of the rib: Cranial and caudal costal facets of adjacent vertebrae; a ball and also socket synovial jointTubercle of the rib: Transverse process of vertebrae; a plane synovial jointLigamentsRadiate longitudinal ligamentIntercapital ligamentCostotransverse ligamentLigament of the neck

Lumbar Spine

Joints

Horses usually have actually 6 lumbar vertebrae (L1-L6), yet some arabian horses only have actually 5 (L1-L5).<1>

Articular processes

Cranial articular processes space fused through mammillary processes. They space concave dorsally and mostly in sagittal alignment. Caudal processes space convex ventrally and correspond through the convexity that the cranial articular processes. They are identified from the last thoracic vertebra by the absence of costal facets.<1>

Motion: The lumbar spine and caudal thoracic spine are the the very least mobile regions of a horse"s back.<8> Lateral flexion and rotation is very restricted especially at L4-L6 as result of intertransverse joints.<1>

Ligaments the Thoraco-Lumbar SpineSupraspinous ligament: A hefty band of connective tissue running end the top of spinous procedures ( T2/T3 caudally). It prevents abnormal separation the spinous processes throughout flexionVentral longitudinal ligament: point out the ventral surface of vertebrae native the axis come the sacrum. The is strongest and also widest caudally. The plays a significant role in preventing overextension the the spineDorsal longitudinal ligament: Extends from the floor of the vertebral canal native the axis come sacrum and helps to protect against spine hyper-flexionAnnulus fibrosis that IVD: special ventrallyIntertransverse ligament

Lumbosacral Joint

The cranial articular procedure of the first sacral vertebra room concave and also face dorsomedially.

Motion: Flexion and Extension - 23.4 degrees<9>

Sacrum

The sacrum consists of fused sacral vertebrae and also has dorsal and ventral sacral foramina.


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Myology and Neurology

Muscles the the Head

Muscles the the Face

The muscles of face expressions are innervated by the engine fibers the CNVII (facial nerve).<1>

MuscleOriginInsertionAction
M. Levator labii maxillarisLacrimal, Zygomatic and Maxillary bonesThe maxillary lipElevates the Maxillary lip
M. Levator nasolabialisNasal and also Frontal bonesThe lateral wing of nostril

The maxillary lip

Elevates and also retracts the angle of the mouth
M. ZygomaticusThe fascia extending the MasseterThe commissure that the lips
M. BuccinatorMaxilla and also MandibleFlattens the cheeks and thus presses food in between the teeth
M. Depressor labii mandibularsThe alveolar border that the MandibleThe mandibular lipDepresses and also retracts the mandibular lip
M. Orbicularis orisThe sphincter muscle of the skin and the muscle of the lips

Corner the the mouth

Into the lips as it surrounds the mouthCloses the mouth
M. RisoriusPart that M. Cutaneous facieiThe edge of the mouthRetracts the angle of the mouth
M. Dilator narisAlar cartillageAlar cartillageDilates the nostril
M. Lateralis nasiDorsal part

Nasal bone

Parietal cartilage

Dilates the nostril and nasal vestibule
Ventral partNasal process of Incisive boneLateral wall of the nasal vestibule
M. CaninusMaxilla close come the rostral extreme of the face crestLateral wing of the nostrilDilates the nose laterally
M. Levator nasolabialisFrontal and also Nasal bonesLateral wing of the nostrilElevates the maxillary lip and also the commissure of the mouth

Dilates the nostril

Ear

The ear is an organ of hearing and also balance. It consists of the outer, middle, and also inner ear.

Outer Ear

The outer ear includes:<1>

Ear canal

Cartilage: Cartilages the the ear collect and transmit sound to the necessary organ of hearing within the temporal bone. In stimulate to attain this, they (especially the concha) must move.<1>

The muscles of external ear:<1>

RostralDorsalCaudalVentral

There are 3 cartilages:<1>

Conchal: forms the frame of the part of the ear which stands erect. It has actually a large vertical opening on one side to receive sound, and also is attached below to the annular cartilageAnnular: A little ring that gristle associated to the auditory procedure of the petrous temporal boneScutiform: A small, flat and somewhat triangular cartilaginous plate located in former of the base of concha, come which the is attachedMiddle Ear

The middle ear includes:<1>

EardrumSmall, air-filled room containing 3 tiny bones: the hammer, anvil, and also stirrup. It likewise includes 2 muscles: the oval window, and also the eustachian tube.Inner Ear

The inner ear is a complicated structure that has the cochlea and the vestibular system.<11>

Muscles that Mastication

The muscles of mastication space innervated by the mandibular branch that trigeminal nerve CNV.<1>

MuscleOriginInsertionAction
M. MasseterThe zygomatic arch and the facial crestThe lateral border of the ramus the the mandibleCloses the mouth
M. TemporalisThe temporal fossa and also the temporal crestThe coronoid process of the mandibleCloses the mouth (to advanced the mandible)
M. Pterygoideus medialisThe crest formed by the pterygoid procedures of the basisphenoid and the palatine bonesThe medial surface ar of the ramus that the mandible
M. Pterygoideus lateralisThe pterygoid procedure of the sphenoid boneRostral border the the condyle that the mandibleDraws and moves the mandible rostrally
M. DigastricusThe jugular process of occipital boneMedial surface ar of the ventral border the the molar part of the body of the mandibleOpens the mouth
M. OccipitomandibularisThe jugular processThe caudal border of the ramus the the mandible
Muscles of the EyesM. Orbicularis oculi - innervated by palpebral branch that CN VIIM. Levator palpebrae superioris - originates from the posterior orbit and also inserts in ~ orbicularis oculi fibers of the reduced eyelid. It elevates the upper eyelid and also is innervated by CN III (oculomotor nerve)M. Malaris - lowers the ventral eyelid. It is innervated by CN VII (facial nerve)Muller"s muscle - innervated by sorry nervesCiliary musclesM. Retractor anguli - retracts and also anchors the lateral canthusMuscles that the Tongue

The horse tongue is comprised of twelve different muscles<14> including styloglossus, genioglossus and also hyoglossus. This muscles space covered through mucosa top top the sides and also underneath.<1>

Action: prehension, mastication (i.e. Chewing)

Innervation: Hypoglossus (CNXII)

Muscles that Pharynx and also Soft palate.<15><16>MuscleOriginInsertionActionInnervation
INTRINSIC MUSCLES
M. Tensor veli palatiniMuscular process of the petrous part of the temporal bone, pterygoid bone, and also lateral lamina the the hear tubePalatine aponeurosisRetracts the soft palate far from the dorsal pharyngeal wall, expanding the nasopharynx and also slightly depressing it ventrad throughout inspirationMandibular branch that the trigeminal nerve
M. Levator veli palatiniMuscular process of the petrous component of the temporal bone and also the lateral lamina the the listening tube and passes follow me the lateral wall of the nasopharynxSoft palate dorsal come the glandular layerElevates the soft palate throughout swallowingPharyngeal branch the the Vagus nerve
M. PalatinusCaudal aspect of the palatine aponeurosisCaudal cost-free margin of the soft palateShortens the soft palate and depresses it in the direction of the tongue
M. PalatopharyngeusPalatine aponeurosis and from the palatine and pterygoid bonesUpper leaf of the thyroid cartilage
M. StylopharyngeusRostralMedial surface of the rostral end of the Stylohyoid bonePharyngeal raphePharyngeal constrictorGlossopharyngeal nerve
CaudalMedial element of the caudal third of the Stylohyoid boneDorsolateral wall of the pharynxPharyngeal dilator
EXTRINSIC MUSCLES
M. GenioglossusMedian aircraft of the TongueOral surface ar of the MandibleProtracts the tongueHypoglossal nerve
M. GeniohyoideusMedial surface of the MandibleBasihyoid boneProtrudes the tongue
M. ThyrohyoideusLateral lamina the the Thyroid cartilageCaudal facet of the thyrohyoid boneMoves the larynx rostrad
M. HyoglossusHyoid bonesMedian plane of the dorsum that the tongueRetracts and also depresses the base of the tongue
M. Hyoepiglotticus
M. StyloglossusLateral facet of the stylohyoid boneTip of the tongueRetraction the the tongue
M. SternohyoideusSternal manubriumBasihyoid bone and also lingual process of the hyoid apparatusCaudal tractionBranches the the an initial and second cervical nerves
M. SternothyroideusCaudolateral element of the thyroid cartilage
Muscles of the Hyoid Apparatus and also Larynx

Muscles the the hyoid apparatus and larynx room innervated by CNX.

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Hyoid Apparatus

The hyoid apparatus has muscular connections from the throat to the forelimbs, shoulder, and sternum. Sternohyoid and omohyoid provide a direct connection from the hyoid device to the shoulder the the equine via the ventral neck. The tongue connects to the hyoid apparatus. Tiny muscles of the hyoid apparatus affix to the TMJ and also the poll and also the TMJ articulates through the hyoid apparatus.<17><18>

Larynx

Intrinsic muscles:

Cricoarytenoideus dorsalis - kidnapping of arytenoids and also tensing of vocal cordsThyroarytenoideus - adduction that arytenoidsArytenoideus transversus - adduction that arytenoids

Muscles that Cervical spine

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