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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.
Long incomplete longitudinal fractures of the third metacarpal and metatarsal bone in horses. Five horses with long incomplete longitudinal fractures of the third metacarpal bone and three horses with similar fractures of the third metatarsal bone were examined. In three of the metacarpal fractures a long incomplete fissure extended proximomedially, in association with the more common lateral condylar fracture of the third metacarpal bone, and in the other two cases the fracture originated from the medial aspect of the distal articular surface. In the three horses with fractures of the third metatarsal bone the fractures had a consistent spiral configuration.
The angiocardiographic diagnosis of a persistent truncus arteriosus in a foal. Persistent truncus arteriosus is a relatively rare cardiac anomaly which is associated with a single large artery arising from the ventricles. An interventricular septal defect is invariably present. The vessel gives origin to the pulmonary trunk, aorta and coronary arteries. A description of the angiocardiographic diagnosis of this condition is given as well as a general review of the relative developmental anatomy.
Observations on the colic motor complex in a pony with a small intestinal obstruction. Characteristic motility patterns were seen throughout the gastrointestinal tract in a pony prepared chronically with electromechanical recording devices after developing a simple obstruction of the small intestine. Gross distension of the stomach with fluid produced loss of gastric contractile activity and a chaotic electrogram. These changes were reversed instantaneously when the stomach was decompressed. In the jejunum, proximal to the obstruction, the unique 'colic motor complex' was observed with contractions of longer duration arranged in characteristic pulses of activity. The left dorsal...
Atresia of the right atrioventricular orifice with complete transposition of the great arteries in a horse. The heart of a 6-week old Arabian filly with a history of poor health and exercise intolerance revealed at postmortem examination, multiple cardiac malformations which included atresia of the right atrioventricular orifice (tricuspid atresia, with associated atrial and ventricular septal defects), complete transposition of the great arteries, anomalous drainage of the venae cavae and coronary sinus into the left atrium, coarctation of the aorta, and a small but patent ductus arteriosus. The course of blood through the heart was suggested and discussed.
Correlative morphometry and morphology of normal equine intestinal mucosa and comparison after adaptation to extensive large colon resection. Light microscopy, morphometry and scanning electron microscopy (SEM) were used to examine the mucosal morphology of seven intestinal specimens (three from the small intestine and four from the large intestine) from two horses not subjected to surgery and three horses one year after sham-operation for colon resection. Qualitative and quantitative evaluation revealed similar morphology for all horses except that the unoperated horses had significantly (P < 0.05) fewer goblet cells in the crypts of the large intestine. In the small intestine, SEM demonstrated that villus shape varied and range...
Vascular anatomy of the equine small colon. The vasculature of 22 small colons from dead adult ponies was perfused with latex or barium sulphate solution. The vascular anatomy was studied by use of dissection and alkali digestion of the latex specimens and microangiography of the barium sulphate-perfused specimens. The small colon is supplied by the caudal mesenteric artery. The left colic artery arises from the caudal mesenteric artery, which then becomes the cranial rectal artery. Branches from the left colic and cranial rectal arteries form anastomosing arcades that become narrower distally along the length of the small colon. From t...
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.
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.
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.
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...
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.
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 ...
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...
