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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.
Heterogeneity of pericyte populations in equine skeletal muscle and dermal microvessels: a quantitative study. The objective of this ultrastructural investigation was to determine if populations of pericytes in equine dermal and skeletal muscle capillaries increase in a head-to-foot direction, as has been reported in human skeletal muscles. Samples of equine microvessels were obtained from the longissimus dorsi skeletal muscle 150 cm. from the ground, from the dermis above this muscle, from the extensor carpi radiali muscle at 55 cm. from the ground, from the dermis adjacent to that muscle, and from dermis 15 cm. from the ground, just above the hoof wall. Tissues were processed for transmission electro...
Differential distribution of immunoreactive S-100 protein in mammalian testis. The present study deals with the immunohistochemical localization of S-100 protein in the testes of seven mammalian species including rat, cat, dog, pig, sheep, cattle and horse. Significant differences are demonstrated in the cellular distribution and intensity of immunoreaction for the protein. In bull, ram, boar and cat testes S-100 protein was localized in the cytoplasm and nuclei of Sertoli cells. A particularly intense staining was seen in the modified Sertoli cells of the terminal tubular segment. With the exception of the cat and horse S-100 protein immunoreactivity was additionally fo...
Abdominal radiography for diagnosis of enterolithiasis in horses: 141 cases (1990-1992). Medical records of 245 horses that had been evaluated by use of abdominal radiography between January 1990 and December 1992 were reviewed. One hundred forty-one horses subsequently had a postmortem examination or surgical exploration performed for definitive lesion diagnosis. The signalment, diagnosis, site, and number of enteroliths were obtained from the medical records. Radiographs were evaluated individually by 3 reviewers for the presence of enteroliths, preferred diagnostic view, evidence of large colon tympany, and film quality. Of the 141 cases reviewed, 66.7% (94/141) had confirmed e...
Functional anatomy of tendons and ligaments in the distal limbs (manus and pes). Tendons and ligaments of the equine distal limbs have a prominent anatomic, functional, and clinical importance. This article reviews the descriptive and topographic anatomy of these structures in details. Special information is given about the mechanical properties and functional anatomy of the flexor tendons, accessory ligaments, and third interosseous muscle, as well as about their roles during the standing position and gaits.
Measurements of blood flow and xanthine oxidase activity during postischemic reperfusion of the large colon of ponies. To assess right colic artery blood flow and relevance of xanthine dehydrogenase/xanthine oxidase after experimentally induced strangulation obstruction and reperfusion of the colon, 5 ponies were subjected to 2.5 hours of complete ischemia of the left dorsal and ventral colons, allowed to recover from surgery, and monitored during a 48-hour reperfusion period. Five ponies were subjected to sham surgery and served as controls. All ponies had a Doppler ultrasound blood flow monitor implanted on the right colic artery near the pelvic flexure 10 to 14 days prior to the ischemic period. Colic arter...
Substance P and calcitonin gene-related peptide-like immunoreactive nerve fibers in lungs from adult equids. Distribution of pulmonary nerves immunoreactive for either substance P or calcitonin gene-related peptide was determined, using immunohistochemical methods on healthy lungs from adult equids. The overall patterns of distribution of substance P and calcitonin gene-related peptide-like immunoreactivity were similar. Distribution of immunoreactive nerves was not uniform throughout the lungs; nerve fibers immunoreactive for these peptides were more frequently observed near the hilus of the lung than in the caudal lobes or in the periphery of the lung. Nerve fibers immunoreactive for substance P or...
Is dentition an accurate indication of the age of a horse? It is widely accepted that the age of a horse can be determined from an examination of its teeth, but there is no evidence that the accuracy of the systems of ageing used has been validated. A dental record was made of 80 horses of known age. There was a good correlation between the actual and apparent age of the horses up to five years, but older horses showed much greater variability and accuracy declined markedly after 11 years of age. The disappearance of the 'cup', but not the 'mark', proved to be one of the more reliable features. The average age at which the dental star appeared was one...
Endoscopic anatomy and map of the equine bronchial tree. To develop a bronchoscopic map of the equine respiratory tree, the major airways of the lungs of 6 healthy Thoroughbred horses were systematically explored with a flexible fibreoptic endoscope through a tracheostomy while the horses were sedated in stocks. With the carina as the reference point, measurements were made of distances to the branches of the major airways using markers on the shaft of the endoscope. All branches were explored until the narrowing of their diameters prevented further advancement of the endoscope. Positions of origins of branches from the parent bronchus were recorded...
The structure, innervation and location of arteriovenous anastomoses in the equine foot. In the foot of the horse, arteriovenous anastomoses (AVAs) of epithelioid type occurred in the dermis of the coronary band, in the coronary and terminal papillae, in neurovascular bundles and at the entrance to and along the length of the dermal laminae. A particular feature of the epithelioid segment of AVAs in the horse, compared with that of other species, was the height and surface complexity of many of the endothelial cells. They extended into the lumen, forming undercut and tunnel-like areas which correlated with the characteristic surface marking of AVAs observed in vascular casts. The ...
Comparative aspects of the strength of pulmonary capillaries in rabbit, dog, and horse. In previous studies of rabbit and dog lung, we demonstrated stress failure of pulmonary capillaries at high transmural pressures (Ptm). The Ptm necessary to elicit stress failure was 40 cmH2O higher in dog than rabbit, and the total blood-gas barrier (BGB) thickness was greater in dog than rabbit. This suggests that stress failure may be related to BGB thickness, and is consistent with the Laplace relationship which states that wall stress is proportional to capillary radius but inversely proportional to wall thickness. In the present studies, we compared BGB thickness and an index of capillar...
In vitro mechanical properties and failure mode of the equine (pony) cranial cruciate ligament. In vitro failure modes and mechanical properties of the equine cranial cruciate ligament (CCL) were evaluated in 15 stifle joints from 10 ponies. Ponies were from 3 to 25 years of age and weighed from 122 to 208 kg. Femur-CCL-tibia specimens were mounted in 48 degrees of flexion, distracted until a 500-g tensile preload was achieved, and then tested by tensile loading to failure. Specimens failed by complete midsubstance CCL rupture (n = 9), combined tibial insertion avulsion fracture and midsubstance CCL rupture (n = 4), and combined femoral origin avulsion fracture and midsubstance CCL ruptu...
Causes of death in racehorses over a 2 year period. Necropsies were performed on 496 horses that had a fatal injury or illness at a California racetrack during the period February 20th 1990 to March 1st 1992. The primary cause of death was categorised by breed, activity at time of injury or illness and organ system affected. Most of the submissions were Thoroughbred horses (432) and Quarter Horses (46). Most of the injuries occurred while racing (42%) and in training sessions (39%); with fewer non-exercise (12%) and accident (7%) related injuries or illnesses. Musculoskeletal injuries accounted for 83% of the Thoroughbred and 80% of the Quarter...
Sensory nerve conduction velocity of the caudal cutaneous sural and medial cutaneous antebrachial nerves of adult horses. Maximal conduction velocities of compound action potentials evoked by stimuli of 2 times threshold in the caudal cutaneous sural (CCSN) and medial cutaneous antebrachial (MCAN) nerves were determined by averaging potentials evoked and recorded through percutaneous needle electrodes. Mean maximal conduction velocities of compound action potentials were: CCSN = 61.3 +/- 2.0 meters/second (m/s) and MCAN = 56.4 +/- 2.8 m/s. To confirm accuracy of our percutaneous recordings, compound action potentials were recorded through bipolar chlorided silver electrodes from the exposed surfaces of fascicles ...
Attempts to modify reperfusion injury of equine jejunal mucosa using dimethylsulfoxide, allopurinol, and intraluminal oxygen. This study compared the severity of ischemic injury to the equine jejunal mucosa caused by arteriovenous obstruction (AVO) or venous obstruction (VO) with that caused by reperfusion after ischemia. The degree of mucosal damage and regeneration was scored according to a modified version of an established light microscopic classification for ischemic injury. Biopsy specimens taken after 3 and 4 hours of obstruction, and after 3 hours of obstruction and 1 hour of reperfusion, were compared. There were no changes in the severity of mucosal injury (characterized by epithelial sloughing, loss of vil...
Effect of ligation on internal carotid artery blood pressure in horses. The effect of a single ligature on back pressure in the internal carotid artery was studied in nine horses. In six anesthetized horses, one internal carotid artery was catheterized 2 cm from its origin and blood pressure was recorded continuously. Then the artery was ligated, pressure was recorded again, and the horses were euthanatized. In another three anesthetized horses, indwelling catheters were placed in both internal carotid arteries and a loose ligature was placed proximal to one catheter. After horses recovered from anesthesia, the ligature was tied and blood pressure was recorded in ...
Carpal conformation in relation to carpal chip fracture. An objective radiological method of assessing the degree to which horses are conformationally 'back at the knee' (hyper-extended) is described. The effects on the measurements of variations in the direction of the incident X-ray beam and variations in weight bearing by the horse were assessed. A change from a lateromedial projection towards a plamaro-lateral-dorsomedial oblique projection consistently tended to reduce the observed degree of hyperextension of the carpus. Raising the contralateral limb to increase the load on the carpus had little effect on the measurements. The carpi of 21 thor...
Bilateral hind limb hypoplasia in a foal. Hypoplasia affecting both hind limbs was observed in a neonatal foal. Scintigraphy aided in establishing diagnosis and prognosis. Radiography revealed an abnormally shaped middle phalanx and lack of the distal phalanx and navicular bone in the right hind limb, with an abnormally shaped distal phalanx and navicular bone in the left hind limb. Scintigraphic findings were closely correlated with the radiographic findings. Radiographic and scintigraphic findings were confirmed at postmortem examination.
Structure of the equine infectious anemia virus Tat protein. Trans-activator (Tat) proteins regulate the transcription of lentiviral DNA in the host cell genome. These RNA binding proteins participate in the life cycle of all known lentiviruses, such as the human immunodeficiency viruses (HIV) or the equine infectious anemia virus (EIAV). The consensus RNA binding motifs [the trans-activation responsive element (TAR)] of HIV-1 as well as EIAV Tat proteins are well characterized. The structure of the 75-amino acid EIAV Tat protein in solution was determined by two- and three-dimensional nuclear magnetic resonance methods and molecular dynamics calculatio...
Structural organization and neuropeptide distributions in the equine enteric nervous system: an immunohistochemical study using whole-mount preparations from the small intestine. The architecture and neurochemistry of the enteric nervous system was studied by use of whole-mount preparations obtained by microdissection of the horse jejunum. A myenteric plexus and two plexuses within the submucosa were identified. The external submucosal plexus lying in the outermost region of the submucosa had both neural and vascular connections with the inner submucosal plexus situated closer to the mucosa. Counts of neurones stained for NADH-diaphorase demonstrated the wide variation in size, shape and neurone content of individual ganglia in both the external and internal submucosal...
Sir Frederick Hobday Memorial Lecture. Some observations on condylar fractures of the third metacarpus and third metatarsus in young thoroughbreds. The common spontaneous fractures of the third metacarpus and
metatarsus of young racehorses are split cannons or condylar
fractures. Meagher (1976) described a series of 45 cases involving
the lateral condyle and Richardson (1984) detailed 15 cases involving
the medial metatarsal condyle. Rick et al. (1983) published a clinical
and pathological study of 75 cases of third metacarpal and metatarsal
condylar fracture. In the United Kingdom, Barr et al. (1989) recorded
8 cases with long fractures, 3 lateral and 5 medial condylar. This
paper reports 124 cases of medial or lateral condylar f...
Accessory carpal bone fractures in the horse. The clinical signs, the radiographic appearance, and the treatment of two cases of fracture of the accessory carpal bone are described. The fractures were in the vertical plane. Surgical intervention consisted out of fixation of the fracture with two lag screws. Follow-up information revealed that one horse became sound and returned to complete athletic activity whereas the other horse remained lame. A brief literature review is given and the surgical treatment and the complications are discussed.
Torsion in quadrupeds and its impact on mammalian joints. Congenital and acquired torsion occur in the limbs of domestic animals. Congenital abnormalities are of clinical significance in foals; they are also seen in calves whose dams have ingested certain toxic plants that contain teratogenic agents. Acquired torsional deformities are most common in foals, but are also observed in adult horses, dogs, and llamas. Acquired rotational deformities are almost always associated with angular limb deformities. The clinical consequence of torsional deformities is the early development of degenerative joint disease.
A silver-impregnation and immunocytochemical study of innervation of the distal sesamoid bone and its suspensory ligaments in the horse. The innervation of the navicular bone (os sesamoideum distale) and its suspensory ligaments (ligamenta sesamoidea collateralia) (CSL) or proximal suspensory ligament and the ligamentum sesamoideum distale impar or the distal sesamoidean impar ligament (DS-impar ligament) was examined using combined anatomical techniques of silver impregnation and immunocytochemistry. Silver impregnation studies revealed an abundance of nerve fibres present in both the CSL and DS-impar ligament with the latter having relatively more nerve fibres. These silver-impregnated nerves coursed parallel to and were asso...
Vascular perfusion in horses with chronic laminitis. Vascular perfusion casts were used to define and characterise the macroscopic perfusion defects present in the distal digit of 11 horses affected by chronic laminitis. Five clinically normal horses were used as controls. Based on clinical history and clinical status, horses with chronic laminitis were classified as being potentially treatable or clinically refractory. Eleven macroscopic vascular defects were noted in the casts from horses with laminitis. Four types of lesions were identified in the submural laminar circulation, 3 in the coronary bed and 4 were associated with the solar circula...
Contact area and pressure distribution changes of the equine third carpal bone during loading. Changes in contact area and pressure distribution with loading were evaluated on the proximal articulating surface of the equine third carpal bone using safranin-O dye staining and pressure sensitive film techniques. A significant increase in percentage contact area resulted as the applied load was increased from 3115 to 9000 N (54.93% +/- 7.99 vs 61.43% +/- 7.37 respectively, P = 0.016). The area in contact shifted towards the dorsal aspect of both the radial and intermediate facets of the third carpal bone. Changes were also detected in the mean pressure under the same loading conditions. Th...
Changes in respiratory muscle activity in ponies when end-expiratory lung volume is increased. The objective of the present study was to determine whether lung and diaphragm afferents contribute to the changes in respiratory muscle activity when end-expiratory lung volume (EELV) is changed in ponies. We studied the responses of the diaphragm and the transversus abdominis (TA) muscles to passive increases in EELV in awake intact (I), diaphragm-deafferented (DD), pulmonary vagal- (hilar nerve) denervated (HND), and DD + HND ponies. Negative pressure of -10 or -20 cmH2O applied around the ponies' torsos [positive transrespiratory (TR) pressure] increased (P < 0.05) EELV in all ponies; t...
Nerve supply of the proximal sesamoid bone in the horse. In chronical proximal sesamoid bone lameness it is difficult to localise the exact site of pain. A specific diagnostic analgesia is not available because of a deficiency of detailed information about the nerve supply to the proximal sesamoid bones and surrounding area. A macroscopic study of the nerve distribution to the proximal sesamoid bones of 10 foals and 5 adult horses revealed that these bones are innervated by two branches, in this study called the medial and lateral sesamoidean nerve, respectively, originating from the medial and lateral palmar nerve. Histology of the left forelimbs o...
