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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.
Ultrasonography as a method to determine tendon cross-sectional area. Ultrasonographic cross sectional area (CSA) measurements of equine superficial digital flexor (SDF) tendon were obtained to determine the feasibility of ultrasonography for CSA measurement of tendon in vivo and in vitro. Ultrasonographic measurements were compared with a more traditional CSA measurement method, ink-blot analysis. In addition, values for ultrasonographic SDF tendon mean echogenicity were obtained in vivo and in vitro. The left forelimb SDF tendons of 23 horses were evaluated ultrasonographically. Cross sectional images were acquired at 4-cm intervals distal to the base of the a...
Racing performance after hemicircumferential periosteal transection for angular limb deformities in thoroughbreds: 199 cases (1987-1989). Racing records of 199 Thoroughbred foals with angular limb deformities surgically treated by hemicircumferential periosteal transection and elevation (HCPT) from 1987 through 1989 (principals) were compared with records of their 1,017 siblings (controls) for starting status; 2-, 3-, and 4-year-old starts; earnings and earnings per start; and starts percentile ranking number (SPR). Principals had a slightly lower percentage of horses starting a race (45 vs 55%), fewer 2-year-old starts (1.06 vs 1.72), and lower SPR (33.49 vs 49.18), compared with those of controls (P < 0.05). Starting status...
Retrograde contrast radiography of the distal portions of the intestinal tract in foals. A technique for retrograde contrast radiography of the distal portions of the intestinal tract of foals was developed and then performed in 25 foals (1 to 30 days old) with colic. Retrograde contrast radiography was shown to be sensitive (100%) and specific (100%) for evaluating obstruction of the small colon or transverse colon. It was slightly less sensitive (86%) and specific (83%) for evaluation of the entire large colon, particularly in older foals. Retrograde contrast radiography provided increased diagnostic capability, compared with that for noncontrast radiography. Retrograde contrast...
Skeletal growth rates of weanling and yearling thoroughbred horses. This study was conducted to determine normal rates of growth of different skeletal segments in the thoroughbred horse. Growth of body weight and eight skeletal segments (wither height, hip height, body length, knee to pastern length, hock to pastern length, shoulder to pastern length, width of chest, depth of girth) were monitored in 106 horses (60 colts, 46 fillies) during the period from 14 to 588 d of age. Body weight gains were slightly higher (30 to 40 kg) than previously reported values. Growth in wither height and hip height were similar to previous reports. During the period measured i...
Role of navicular bone shape in the pathogenesis of navicular disease: a radiological study. From progeny lists of 30 Dutch Warmblood sires, 586 3-year-old females by these stallions were randomly selected, each progeny group aimed at 20 animals for statistical reasons. The front feet of the sires and female progeny were examined radiographically using lateromedial and dorsopalmar upright pedal projections. The radiological features associated with navicular disease were classified 0-4 using a standardised classification, grades 3 and 4 representing the more severe changes. The shape of the proximal articular border of the navicular bone outline on the dorsopalmar view was classified ...
Ultrastructure of the secretory endometrium during oestrus in young maiden and foaled mares. Cyclical accumulation of uterine fluid occurs during oestrus and is often seen in excessive volumes in mares considered susceptible to endometritis. Since the mechanisms behind the formation of free uterine fluid remain to be clarified, the fine structure of the secretory equine endometrium was studied in biopsies collect during videoendoscopy from 14 endometritis-free, 4-9-year-old mares during oestrus. A distinct oedema of the tunica mucosa was evident. The surface epithelium had both ciliated and nonciliated cells and, particularly at the uterine body, often presented intra-epithelial macro...
Localisation of 15-hydroxy prostaglandin dehydrogenase (PGDH) and steroidogenic enzymes in the equine placenta. 15-hydroxy prostaglandin dehydrogenase (PGDH) is the critical enzyme that determines metabolism of primary prostaglandins. Its expression is determined in part by steroid hormones, particularly progesterone, formed from delta(5) steroids through 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity. To assess whether the regulation of PGDH might occur in a paracrine, autocrine or intracrine fashion, we used immunohistochemistry (IHC) to determine the localisation of key steroidogenic enzymes in the equine placenta and compared these patterns to the distribution of immunoreactive (IR-) PGDH. ...
Echocardiographic measurements of cardiac dimensions and indices of cardiac function in normal adult thoroughbred horses. Cardiac dimensions and indices of cardiac function were measured in 29 clinically normal adult Thoroughbreds (TB) which performed minimal exercise using guided M-mode and two-dimensional (2-D) echocardiography, from a variety of image planes and measurement methods, and standardised imaging planes based on intracardiac anatomical landmarks. The different methods of measuring these variables were compared. The variables which were considered to be most valuable for quantitative echocardiography were measured in a further 9 horses. Comparable measurements of cardiac dimensions can be obtained fr...
Evidence of strain-mode-related cortical adaptation in the diaphysis of the horse radius. The relative importance that certain strain features, including mode (e.g., tension vs. compression) and magnitude, have in affecting adaptive bone remodeling seen in normal skeletally mature bones remains controversial. The equine radius is used as a model because in vivo strain data show that the mid-to-proximal diaphysis receives a consistent history of predominantly cranial-caudal bending loads, in contrast to the distal diaphysis which receives relatively more torsional loading superimposed on cranial-caudal bending. Medial and lateral cortices serve as control regions because they corres...
Scintigraphy for diagnosis of avulsions of the origin of the suspensory ligament in horses: 51 cases (1980-1993). The medical records of 34 horses with a diagnosis of avulsion of the origin of the suspensory ligament that had been admitted to the veterinary medical teaching hospital between 1980 and 1993 were identified. In addition to clinical examination, 21 of 34 horses had scintigraphy and radiography performed during their examination. The usefulness of scintigraphy and radiography were assessed by comparing the initial findings reported in the medical record to those obtained in a retrospective review of the images. Thirty other horses with scintigraphic lesions of the proximal aspect of the third m...
Echocardiographic measurements of cardiac dimensions in normal ponies and horses. Echocardiographic examinations were performed on 41 clinically normal small ponies, large ponies and horses. Using standardised two-dimensional (2-D) echocardiographic images to guide M-mode studies, the interventricular septal thickness, left ventricular internal dimension and left ventricular wall in systole and diastole, and aortic diameter in diastole were measured. Normal values for these echocardiographic dimensions were obtained across a wide range of bodyweights. Although there was a trend for echocardiographic dimensions to increase with bodyweight across the whole range of animals ex...
Unilateral choanal atresia in a foal. A 4-month-old Thoroughbred foal was examined because of a history of exercise intolerance and lack of airflow from the right nostril since birth. Endoscopy of the airways revealed complete membranous obstruction of the right nasal passage at the level of the nasopharynx and marked narrowing of the caudal aspect of the right ventral meatus. Unilateral choanal atresia was diagnosed. Laser ablation of the obstructing tissues was attempted through a videoendoscope. Scar tissue occluded the right nasal passage at follow-up examination 7 weeks later. Intranasal resection, using laparoscopic instrume...
Ligaments associated with joints. This article contains a short introduction to the anatomy, physiology, and pathophysiology of ligaments associated with diarthrodial joints. Individual ligaments are discussed on a regional basis as forelimb, distal limb, and hindlimb. Emphasis is placed on the anatomy of the ligaments because this is the key to sound clinical application of their involvement in joint disease. There are few conditions of diarthrodial joints that do not involve their associated ligaments, and this role may be in causative, diagnostic, and therapeutic or convalescent considerations.
Aseptic tenosynovitis of the digital flexor tendon sheath, fetlock and pastern annular ligament constriction. The anatomy of the digital flexor tendon sheath and related tendons and ligaments is described. Diagnosis and management of acute tenosynovitis and long-term tenosynovitis and associated tendon injuries are discussed, as well as the syndrome of stenosis of the fetlock canal (or fetlock annular ligament constriction) and palmar annular ligament constriction. Desmitis of the palmar annular ligament is also described.
Localisation of alkaline phosphatase in equine growth cartilage. The aim of this study was to localise alkaline phosphatase (ALP) activity in equine growth cartilage both histochemically and ultrastructurally. For histochemical studies, full thickness growth cartilage samples were obtained from 6 anatomical sites from 16 horses and ponies ranging in age from 90 d postconception to 12 years of age. For ultrastructural studies, samples were obtained from the lateral trochlear ridge of the distal femur of 3 animals ranging in age from 157 d postconception to 12 months of age. Alkaline phosphatase in histological sections was localised using a substituted napht...
Equine pelvic flexure myoelectric activity during fed and fasted states. The pelvic flexure is the midpoint of the equine large colon that marks the junction of dorsal and ventral components. Previous studies of intraluminal pressure in this region indicate that it could be an important motility control center. The present study was undertaken to expand our knowledge of normal myoelectric activity around the pelvic flexure region. Eight bipolar silver wire electrodes were surgically fixed at 5-cm intervals to the colonic serosa of five adult horses, starting 30 cm oral to the pelvic flexure on the left ventral colon and ending 15 cm aboral to the pelvic flexure on ...
Detection of immunoreactive atrial and brain natriuretic peptides in the equine atrium. The distribution of immunoreactivity (IR) for cardiodilatin/atrial natriuretic peptide (CDD/ANP) and brain natriuretic peptide (BNP) was examined immunohistochemically and immuno-electron-microscopically in the equine atrium, using specific antibodies. In the immunohistochemical studies, IR-CDD/ANP and IR-pBNP-26 (porcine BNP-26 immunoreactivity) was detected in the cytoplasm of the auricular cardiocytes, but IR-hBNP-32 (human BNP-32 immunoreactivity) was not. The double immunogold labelling method for IR-hBNP-28 and IR-pBNP-26 revealed that gold particles of different sizes were located in th...
Prothrombotic events in the prodromal stages of acute laminitis in horses. Prothrombotic changes occurring in the prodromal stages of carbohydrate-induced laminitis were investigated. Hemostatic alterations were evaluated by determining platelet counts, platelet survival, activated partial thromboplastin time, one-stage prothrombin time, and monocyte procoagulant activity. Thrombosis of vessels in the hoof wall was evaluated by contrast arteriography and histologic examination. Of 5 horses, 4 became lame between 28 and 52 hours after carbohydrate administration. Mean platelet count in laminitis-affected horses was lower throughout the prodromal stages of laminitis, c...
Subcellular biochemical changes during the development of the small intestine of pony foals. To examine the postnatal development of equine small intestine, biopsy specimens of jejunal mucosa from 8 ponies, between 6 and 28 weeks old, were subjected to analytical subcellular fractionation and assay of organelle marker enzymes. Fractionation revealed a reduction in the particulate brush border component of beta-galactosidase (lactase) activity between 6 and 28 weeks, and a corresponding increase in soluble activity, although the reduction in mean specific activity was not significant. There also was a decrease in the proportion of brush border to soluble aminopeptidase N activity, a re...
Isolation, culture, and characterization of equine oviduct epithelial cells in vitro. Oviduct epithelial cells (OEC) increasingly are used to support embryonic development and to study gamete interactions with the female reproductive tract in vitro. This series of experiments was designed to characterize monolayers derived from oviduct epithelium. Epithelial cells harvested from the isthmus and ampulla of the oviducts of five estrous mares were cultured with or without the basal lamina extract, Matrigel. Within each group OEC were cultured in the presence of either estradiol-17 beta or a carrier control. All groups were subcultured three times. Epithelial cell morphology and fu...
Lymphoid tissues of the ileum in young horses: distribution, structure, and epithelium. Lymphoid tissues in the ileum of young horses form raised plaques that are macroscopically visible from the mucosal surface. These are termed "ileal lymphoid patches". These patches are variable in size, shape and position within the ileal wall, occasionally lying along the site of mesenteric attachment. Within lymphoid patches, follicles exist in three different morphological forms: follicle/dome structures, proprial follicles, and lymphoglandular complexes (LGCs). In follicle/dome structures, the majority of the follicle lies in the submucosa and merges with a dome in the lamina propria thro...
Tendon, tendon sheath, and ligament injuries in the pastern. The palmar (plantar) aspect of the pastern is an anatomically complex area and an understanding of this is a prerequisite for accurate diagnosis of injuries in this area. The gross and normal ultrasonographic anatomy are described, and injuries of the superficial and deep digital flexor tendons and the digital flexor tendon sheath, the distal sesamoidean ligaments, and the palmar ligaments of the proximal interphalangeal joint are discussed.
Miscellaneous conditions of tendons, tendon sheaths, and ligaments. The use of diagnostic ultrasonography has greatly enhances our ability to diagnose injuries of tendons and tendon sheaths that were previously either unrecognized or poorly understood. For may of these injuries, there is currently only a small amount of follow-up data. This article considers injuries of the deep digital flexor tendon and its accessory ligament, the carpal tunnel syndrome soft tissue swellings on the dorsal aspect of the carpus, intertubercular (bicipital) bursitis and bicipital tendinitis, injuries of the gastrocnemius tendon, common calcaneal tendinitis, rupture of peroneus (...
Suspensory ligament desmitis. The gross and functional anatomy of the suspensory ligament (SL) and its ultrasonographic variability are described. Injuries of the suspensory apparatus are divided into lesions confined to the proximal one third of the metacarpus or metatarsus (proximal suspensory desmitis and avulsion fractures), lesions of the body, and branch lesions. Complete breakdown injuries are also discussed. In view of the close association of the SL, the second, third, and fourth metacarpal or metatarsal bones, and the proximal sesamoid bones, associated bony lesions are also considered.
Microscopic anatomy of the equine skin with special reference to the dermis. We have observed and re-evaluated the histology of the skin of the horse, using samples from four Thoroughbreds. The skin was composed of the usual three components: epidermis, dermis and subcutis. In particular, the dermis was found to have three fibrous components: a papillary layer, a reticular layer and a cordovan-leather tissue layer. The cordovan-leather tissue layer was subdivided into a superficial main layer and a deeper accessory layer. The superficial main layer was thick, and present in all of the skin samples. The deeper accessory layer was found in the dorsal and dorso-lateral pa...
An evaluation of the accuracy of ageing horses by their dentition: changes of dental morphology with age. Dental features are commonly expected to provide an accurate estimate of a horse's age. In this study the dentition of 434 thoroughbreds was photographed and the individual dental features documented, the true age of all the horses was known. For each dental feature the correlation with true age was determined. The eruption of the incisor teeth was the most consistent feature but it was not totally reliable. The presence of a hook on the upper corner incisor and Galvayne's groove proved to be of no value when estimating age and, of the attritional features studied, the dental star showed the h...
Metacarpal fracture associated with lymphosarcoma-induced osteolysis in a horse. A 19-year-old Appaloosa gelding was reluctant to move. Radiography revealed diffuse, permeative lysis of the cortex and subchondral bone of the phalanges, third metacarpal bones, proximal sesamoid bones, radius, carpal bones, tibia, mandible, and nasal bones of the skull. A comminuted fracture of the distal aspect of the left third metacarpal bone was identified on a lateral to medial radiographic view of the left metacarpophalangeal joint. Histologic examination of the first phalanx, third metacarpal bone, and sternum revealed multifocal infiltrates of nodular lymphosarcoma in cortical and su...
Cutaneous amyloidosis in a horse with lymphoma. A horse with malignant lymphoma (histiolymphocytic) and cutaneous amyloidosis is described. The lymphoma involved the dura mater of the spinal cord and some of the peripheral lymph nodes. Multifocal amyloid deposits were present in the skin and subcutis of the ventral abdomen but not within the lymphoma cell infiltrates or in the viscera.
