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Topic:Anatomy
Anatomy in horses encompasses the study of the structural organization of the equine body, including the bones, muscles, organs, and systems that function together to sustain life and enable movement. Understanding equine anatomy is important for veterinarians, equine scientists, and horse owners, as it provides insights into how horses move, how they respond to external stimuli, and how various conditions can affect their health and performance. Key anatomical features in horses include the musculoskeletal system, which provides support and locomotion; the cardiovascular system, which circulates blood and nutrients; and the respiratory system, which facilitates gas exchange. This page compiles peer-reviewed research studies and scholarly articles that explore the detailed anatomy of horses, focusing on the structure and function of different body systems, their interrelationships, and their relevance to equine health, performance, and veterinary care.
Xeroradiographic evaluation of the equine larynx. The normal radiographic anatomy of the equine larynx was determine by use of xeroradiography and dissection. The body and laminae of the thyroid cartilage, the muscular process of the arytenoid cartilages, and the dorsal lamina and arch of the cricoid cartilage had radiographic evidence of mineralization (calcification) and/or ossification in clinically normal horses. There was a significant (P less than 0.01) increase in the degree of mineralization of the thyroid and arytenoid cartilages with advancing age. Horses with diagnosis of arytenoid chondrosis (arytenoid chondral dysplasia, arytenoi...
Electromyographic activity of cubital joint muscles in horses during locomotion. Electromyographic (EMG) activity of 4 muscles of the cubital joint and the strain of forelimb hooves were recorded telemetrically in 4 Thoroughbreds (with and without a rider) standing, walking, trotting, and cantering. Bipolar fine wire electrodes were inserted into the muscles, and strain gauges were attached to the hoof wall. Motion pictures (16 mm), synchronized with EMG tracings, were taken to obtain kinematic data. When horses were standing, the biceps brachii had tonic activity, but the brachialis and the caput longum and the caput laterale of the triceps brachii had no EMG activity. Th...
Identification and description of beta-structure in horse muscle acylphosphatase by nuclear magnetic resonance spectroscopy. Nuclear magnetic resonance spectra of acylphosphatase were searched for signs of beta-structure, i.e. characteristic nuclear Overhauser enhancement patterns displayed in the two-dimensional spectra, typical chemical shifts, coupling constants and slow 2H-H exchange. The results provided identification of the main-chain resonances of amino acid residues involved in the beta-structure. The full sequential assignment of this region was gained by identification of some amino acid spin systems and their alignment with the primary sequence. The assignment of the side-chains was virtually completed s...
Morphologic features of the aqueous humor drainage pathways in horses. The iridocorneal angle of the horse was anteriorly lined by a pectinate ligament, consisting of several layers of vertically oriented collagenous beams, that were interrupted by a network of extracellular spaces. The anterior chamber angle consisted mostly of a large uveal trabecular meshwork that was composed of widely-spaced, thick trabeculae. These trabeculae were attached in part posteriorly to extensions of the ciliary body musculature and anteriorly inserted into the prominent pectinate ligament. The corneoscleral trabecular meshwork was shaped hemiobovately and formed the external bound...
Transendoscopic neodymium:yttrium aluminum garnet laser irradiation in horses. A neodymium:yttrium aluminum garnet (Nd:YAG) laser was used to study effects of applying laser irradiation transendoscopically to the corniculate process of the arytenoid cartilage in horses. Dosimetry was established initially in vitro in 10 corniculate cartilages that were irradiated and examined histologically to determine penetration depths at selected power settings. Eleven horses were given xylazine IV and butorphoral tartrate IV, and their left ventricle and corniculate process were irradiated. Six horses had left laryngeal hemiplegia and were euthanatized and necropsied 14 weeks after ...
Monorchidism in the horse. Six horses with monorchidism, identified at surgery for cryptorchidectomy, are reported. All six presented with a single scrotal testis. Following surgical removal of one testis, they were either hormonally, anatomically or behaviourally determined to be geldings. Three other horses reported in the literature are reviewed. Of these nine cases of monorchidism, eight were thought to be caused by testicular degeneration and one by testicular agenesis. The vaginal process was present in all of the former and absent in the latter. The left side was involved in five of these eight horses. In seven, ...
Forces loading the tarsal joint in the hind limb of the horse, determined from in vivo strain measurements of the third metatarsal bone. Strain gauge rosettes were bonded to the dorsal, lateral, medial, and plantar aspects of the third metatarsal bone in the hind limbs of 6 ponies. The maximal compressive principal strain was approximately -600 X 10(-6) m/m, and exceeded the amplitudes of the tensile strains at all aspects of the bone. After transformation, the shear strain and the principal strains parallel and perpendicular to the bone were obtained. The first peak in the bending strain was higher in the dorsal and lateral aspects, and the second peak was higher in the medial and plantar aspects. Young modulus of elasticity w...
Removal of a retropharyngeal foreign body in a horse, with the aid of ultrasonography during surgery. Diagnostic ultrasonography was used during surgery to assist in the removal of a piece of wire from the retropharyngeal region. A 3-year-old Quarter Horse mare was referred with dysphagia of 2 days' duration. Radiography revealed a 9-cm piece of wire located caudodorsal to the larynx. A ventral surgical approach was performed, dissecting along the right side of the larynx and trachea. The surgical field was filled with 0.85% sterile physiologic saline solution. A 5 MHz-mm sector scanner probe immersed in the fluid was able to locate the wire and facilitate the direction and depth of dissection...
Cervical spinal kinematics: a comparison between foals and adult horses. A photographic method was used to measure axial rotation, dorsoventral flexion and extension and lateral bending at each intervertebral joint complex from the occiput to the first thoracic vertebra in spinal segments from 19 foals under 12 months of age and 14 horses over three years of age. Comparisons between the two groups showed that there was a general reduction in cervical spinal mobility with age. For the three types of movement at the eight joints tested, adults' mobility exceeded that of foals in only three cases (axial rotation and lateral bending at the A-O joint, and lateral bendin...
Comparative pulmonary mechanics in the horse and the cow. Pulmonary mechanics and lung volumes were measured in horses and cows to determine if differences in breathing pattern between the two species were due to differences in the mechanical properties of the lungs. Tidal volume (VT) was larger in the horses, while the respiratory rate (fR) and minute ventilation (VE) were higher in the cows. The horses often had a double peak in airflow during inspiration and, or, expiration, while the cows had a single peak during expiration. Measured lung volumes were larger in the horses and they had a higher dynamic lung compliance (Cdyn,L), although the static...
Kinematics of the cervical spine of the adult horse. At least three types of movement, dorsoventral flexion and extension, axial rotation and lateral bending, were shown to occur at each of the intervertebral joints in the cervical spine. Between the first two cervical vertebrae the mean axial rotation was 107.5 degrees, which was 73 per cent of the total axial rotation of the cervical spine. The atlantooccipital joint rotated through a mean of 27 degrees, whereas the remaining cervical joints each had less than 3 degrees of rotatory movement. Dorsoventral flexion and extension were maximal at the atlantooccipital joint, which had an amplitude o...
Fragments of nasogastric tubes as esophageal foreign bodies in two horses. Two horses were referred with fragments of nasogastric tubes as esophageal foreign bodies. Radiography and endoscopy were used to identify the location of the fragments. Portions of the tubes were retrieved by esophagotomy in 1 horse and by manual examination of the oral cavity in the other. Both tubes were friable in focal areas, but were quite pliable over most of the length of the tube.
Clinical examination of the equine foot. The foot is the most common source of limb pain. The problems vary from simple to quite complex. An accurate diagnosis is dependent upon a thorough and detailed knowledge of anatomy and of what is available in the way of ancillary examination techniques. The correction of most foot problems requires an appreciation of a multitude of factors and a thorough knowledge of farrier science.
Bilateral colobomas in a horse. Bilateral true colobomas with retrobulbar cysts located over the optic nerves are described in an 8-year-old Quarterhorse mare with a history of progressive blindness. Colobomas result from the failure of an embryonic fissure to close and retrobulbar cysts result from eversion of the neuroectoderm through the colobomas. It could not be determined whether the small optic nerves and the scars, rosettes and disorganization of the cell layers in the retina were the result of concurrent dysplasia or were secondary to degeneration.
Equine giant cell tumor of soft tissues. During a routine necropsy examination of a 4-year-old standardbred mare, a well-demarcated dermal mass was seen near the right elbow. Grossly, the mass consisted of multifocal variably sized areas of dark brown, firm material that was separated by thin white septa. Histologically, within the individual compartments, there were numerous multinucleated giant cells, macrophages, and free erythrocytes. A diagnosis of giant cell tumor of soft tissues was made.
Pathways between lymph vessels and sinuses in lymph nodes: a study in horses. The pathways through which lymph flows from terminal afferent lymphatics to the lymph sinuses, and from the sinuses to initial efferent lymphatics, were studied in horse lymph nodes by using Microfil casts and electron microscopy. Terminal afferent lymphatics are continuous with the subcapsular sinus through oval holes, about 3 microns wide, along their length, and through larger openings near their end. Other terminal afferents penetrate into the node within trabeculae and are supported by processes across the lumen. They connect with trabecular and medullary sinuses through oval or round hol...
Attempts to restore abduction of the paralyzed equine arytenoid cartilage. III. Nerve anastomosis. The purpose of this project was to attempt restoration of abduction of a recently denervated left dorsal cricoarytenoid muscle in the horse by anastomosing the first cervical nerve to the abductor branch of the left recurrent laryngeal nerve. Ten horses were used in the study. In six horses the left recurrent laryngeal nerve was transected and ligated while the ventral branch of the left first cervical nerve was anastomosed to the abductor branch of the left recurrent laryngeal nerve. The remaining four horses also had the left recurrent laryngeal nerve transected and ligated but had no nerve ...
The treatment of laminitis in horses. The structural and vascular anatomy of the healthy equine foot is compared with the pathologic changes in the foot of horses with acute and chronic laminitis. The structural and vascular abnormalities present in the foot of horses with laminitis are demonstrated in order to explain the abnormal manner in which their feet grow. The medical, surgical, dietary, and endocrine management of acute and chronic laminitis is discussed. Various forms of hoof trimming beneficial to the reestablishment of normal digital perfusion, normal hoof growth, and normal spatial orientation among the distal phalanx...
Occipitoatlantoaxial malformation with duplication of the atlas and axis in a half Arabian foal. An unusual occipitoatlantoaxial malformation is described in a 2-week-old male part Arabian foal that was unable to stand at birth and showed signs of spastic tetraparesis due to a cervical spinal cord compression. There were 2 atlases present. One was fused to the occipital bones. The other articulated with the first atlas and an axis which had a long dens that projected into the vertebral canal. Examination of the ossification centers of the axis indicated partial duplication of that bone.
Small intestinal strangulation caused by Meckel’s diverticulum in a horse. Necropsy of a 12-year-old Quarter Horse mare revealed a blind-end segment of intestine originating from the antimesenteric border of the ileum. The blind-end segment had looped around and strangulated the ileum and 3.5 m of the jejunum.
Clinical anatomy of the equine foot. A review of investigations of the functional anatomy of the equine foot is presented. Emphasis is placed on the relationships of structures involved in the major diseases of the foot.
Overriding vertebral spinous processes in the extinct horse, Equus occidentalis. Lumbar and thoracic vertebrae of the extinct horse, Equus occidentalis, were examined for gross and radiographic evidence of overriding spinous processes. Of 2,661 vertebrae examined, 580 had intact spinous processes. Thirty-six intact spinous processes, which appeared grossly similar to overriding spinous processes in the modern domestic horse, E caballus caballus, were radiographed. Of these 36 vertebrae, 2 had radiographic signs compatible with a radiographic diagnosis of overriding spinous processes, ie, radiographically observed lysis and/or sclerosis. Seemingly, weight bearing or other s...
Pathophysiology of navicular syndrome. Navicular syndrome is a degenerative disorder of the distal half of the flexor surface of the proximal sesamoid bone that is predisposed by faulty foot conformation. In horses that become symptomatic, the faulty conformation results in sustained application of nonphysiologic pressure by the deep digital flexor tendon against the flexor cortex of the bone. This force stimulates an intense bone remodeling response in order to attenuate the pressure. An unfortunate sequela of this response is active hyperemia and edema formation in the medullary cavity of the bone. The edema is organized by fibro...
Muscular dystrophy-like disease in a thoroughbred foal. A 1-month-old male thoroughbred foal, which had difficulty in walking, was killed and examined by histological, histochemical and ultrastructural methods. The muscles of the trunk and upper hind limbs were chiefly affected, and changes in the affected muscles resembled those in muscular dystrophy in man. The type of muscular dystrophy present in this foal and the significance of this disease in thoroughbred horses are discussed. The dystrophy in this foal resembled the limb-girdle type or myotonic dystrophy of muscular dystrophy in man.
Pathophysiology of acute laminitis. This article reviews research findings relating to the pathophysiology of acute laminitis in horses. The data presently available suggest that the onset of the condition may be due to constriction of the postcapillary vessels in the digit, leading to increased capillary hydrostatic pressure and movement of fluid into the interstitial space.
Radiographic examination of the equine foot. A complete radiographic examination of the equine foot consists of properly exposed, processed, and positioned radiographs. For radiographic interpretation, in addition to knowing radiographic signs of disease, a knowledge of normal radiographic anatomy and possible insignificant anatomic variations is necessary.
