Category Archives: Anatomy Of Dog

Respiratory System

The respiratory system (apparatus respiratorius) uses the nose, nasal cavity, pharynx, larynx, trachea, bronchi, and smaller passageways to bring air to the alveoli or sites of gaseous exchange within the lungs. Various structures associated with these passageways modify or regulate the flow of air, serve as olfactory receptors, facilitate water and heat exchange, and make phonation possible. The nasal cavity and the conchae (also called turbinates) warm and moisten the air and remove foreign material. The pharynx serves as a passageway for both the respiratory and the digestive systems. The larynx guards the entrance to the trachea, functions in vocalization, and regulates both the inspiration and the expiration of air. The trachea is a cartilage-reinforced tube lined by ciliated epithelium. It divides into principal bronchi and continues into the two lungs as lobar bronchi, segmental bronchi, bronchioles, alveolar ducts, alveolar sacs, and alveoli. The terminal divisions are located in the elastic, well-vascularized lungs, which passively expand and collapse in response to changes in intrathoracic pressure, created by the action of the muscles of the diaphragm and thoracic wall. The nose (nasus), in a broad Read more […]

Nasal Cavity

The nasal cavities (cava nasi) are the facial portion of the respiratory passageway. They extend from the nostrils (nares) to the choanae, being separated by the nasal septum. The septum () consists of a bony portion (septum nasi osseum), a cartilaginous portion (cartilago septi nasi), and a membranous portion. Each nasal cavity has a respiratory and an olfactory region. Each nasal cavity begins at the nostril with the nasal vestibule and ends with the nasopharyngeal meatus and choana. Each nasal cavity is divided into four principal air channels and several smaller ones (). During development the growth of laminae from the lateral and dorsal walls of the nasal cavity results in the formation of conchae that largely fill the cavity and restrict the flow of air. The air passages thus created between the conchae are called the nasal meatuses. The nostril (naris), the opening into the nasal vestibule, is a curved opening that is much wider dorsomedially than it is ventrolaterally. It possesses more than usual importance, because in some brachycephalic dogs the opening is too restricted and interferes with respiration. Leonard (1956) devised an operation whereby the transverse diameter of the nostril may be increased. The Read more […]


The larynx () is a musculocartilaginous organ guarding the entrance to the trachea, which serves as an air passageway, aids vocalization, and prevents the inspiration of foreign material. The valvular function of the larynx, by means of the epiglottis, is vital, because it is across its inlet that all substances swallowed must pass in their course from the oral pharynx through the laryngeal pharynx to the esophagus. Negus (1949) has described and illustrated the comparative anatomy of the larynx from fish through mammals, and Piérard (1965) studied the dog and other carnivores. The larynx is located directly caudal to the root of the tongue, oral pharynx, and the soft palate, ventral to the atlas. It is approximately 6 cm long in a medium-sized dog, nearly half of this length being occupied by the epiglottic cartilage, which lies at the laryngeal opening. The intrinsic muscles of the larynx control the size of the laryngeal inlet, the size and shape of the glottis, and the positions of the laryngeal cartilages. Sound production with the aid of the larynx serves an important social function in canids (). Vasquez et al. (1990) studied the normal dog larynx by MRI. Cartilages of the Larynx Cavity of Larynx and Laryngeal Read more […]

Cartilages of the Larynx

The laryngeal cartilages (cartilagines laryngis) () are the epiglottic, thyroid, cricoid, arytenoid, sesamoid, and interarytenoid cartilages. Only the arytenoid cartilage is paired. The epiglottic cartilage (cartilago epiglottica) forms the basis of the epiglottis. In outline, the rostral margin of the cartilage forms a thin, dorsally concave triangle with its apex pointing cranially. The epiglottis resembles a sharp-pointed spade. Its laryngeal surface (facies laryngea) formerly aboral surface, is concave and faces dorsocaudally. The opposite lingual surface (facies lingualis), formerly the oral surface, is convex and faces the oral pharynx. The lingual surface is attached to the middle of the body of the hyoid bone by the short, stout hyoepiglottic muscle. On either side of the median mucous fold that covers the muscle is a deep pocket of mucosa, called the vallecula (vallecula epiglottica), which may attain a depth of 1.5 cm. Each vallecula is limited laterally by a small fold of stratifed squamous epithelium running from the lingual surface of the epiglottis near its caudolateral angle to the lateral wall of the laryngeal part of the pharynx. The stalk of the epiglottis (petiolus epiglottidis) is in the form Read more […]

Cavity of Larynx and Laryngeal Mucosa

The cavity of the larynx (cavum laryngis) is divided into five transverse segments: the aditus laryngis, vestibule, vestibular cleft, cleft of the glottis and the infraglottic cavity. The laryngeal inlet (aditus laryngis) () lies directly caudal to the intrapharyngeal ostium bounded by the epiglottis. Air entering or leaving the larynx can travel either by way of the nasal part or by way of the oral part of the pharynx. In lolling (rapid breathing with the tongue hanging out), most of the air passes through the mouth and oral pharynx; in slow, shallow breathing it passes through the nasal cavity and nasal pharynx. The margin of the laryngeal opening forms an imperfect triangle, with the base located caudally. The margin of the epiglottis forms its lateral boundaries and apex. The caudal boundary is formed by the right and left aryepiglottic folds. Each aryepiglottic fold (plica aryepiglottica) () runs from the dorsal portion of the arytendoid cartilage and the closely associated corniculate cartilage to the caudolateral angle of the epiglottic cartilage. Two prominent tubercles that are separated by a deep notch are present in the fold. The more dorsocaudal tubercle, formed by the underlying corniculate process, Read more […]


The bronchial tree (arbor bronchialis) () begins at the bifurcation of the trachea by the formation of a right and a left principal bronchus (bronchus principals [dexter et sinister]). Each principal bronchus divides into lobar bronchi  (bronchi lobares), formerly secondary bronchi, which is the basis for the identification of the lung lobes. These supply the various lobes of the lung and are named according to the lobe supplied. Within the lobe of the lung the lobar bronchi divide into segmental bronchi (bronchi segmentales), which are sometimes referred to as tertiary bronchi. The segmental bronchi and the lung tissue that they ventilate are known as bronchopulmonary segments (segmenta bronchopulmonalia). Ishaq (1980) studied 37 pairs of dog lungs and suggested a system for designating the bronchi. Schlesinger and McFadden (1981) discuss the morphometry of the proximal bronchial tree in six mammalian species. Adjacent bronchopulmonary segments normally communicate with each other in the dog. Various injection and reconstruction techniques have been employed to delineate these segments in the dog (). For bronchoscopic purposes Amis and McKiernan (1986) described a system of letters and numbers to identify lobar, segmental, Read more […]


The mediastinum is the space and the mediastinal pleurae that enclose this space between the right and left pleural cavities. It is divided by the heart into three transverse divisions. The middle division is further divided by the heart into two more divisions dorsal and ventral to it. The cranial mediastinum (mediastinum craniale) () is the portion of the mediastinum lying cranial to the heart that contains the trachea, esophagus, thymus, sternal and cranial mediastinal lymph nodes, and many vessels and nerves. Dorsally it attaches to the longus colli muscles and ventrally it attaches to the sternum. Ventrally it refects over the internal thoracic vessels as they course toward the sternum to pass deep to the transverse thoracis muscles. The ventral mediastinum (mediastinum ventrale) is that portion ventral to the heart that contains the thymus cranially and the phrenicopericardial ligament (lig. phrenicopericardiacum), a band of connective tissue between the fibrous pericardium and the diaphragm. The middle mediastinum (mediastinum medium) () is the portion containing the heart. Here the mediastinal pleura are fused with the fibrous pericardium. A single layer of tissue separates the pleural cavity from the Read more […]


The pleurae are the serous membranes that cover the lungs, line the walls of the thoracic cavity, and cover the structures in the mediastinal space. The pleurae form two complete sacs, one on either side, which are known as the pleural cavities (). Each pleural cavity (cavum pleurae) in life is essentially only a potential cavity, because it contains only a capillary film of fluid which moistens the fat mesothelial cells paving its surface. Except for this capillary fluid, the visceral pleura of the lungs, or pulmonary pleura, lies in contact with the wall or parietal pleura. Only when gas (air) or fluid collects between the pulmonary and parietal pleurae and prevents a lung from expanding does it exist as a real cavity. The right pleural cavity is larger than the left because of displacement of the caudal mediastinal wall to the left side. The pleural cavities do not communicate with each other, although their medial walls and the tissue between them are extremely thin. For purposes of description, the pleura is designated as the parietal and the pulmonary pleura. The parietal pleura (pleura parietalis) forms the walls of the pleural cavities. It is further designated as costal, mediastinal, and diaphragmatic. The Read more […]

Thoracic Cavity

The thoracic cavity (cavum thoracis) (), in a narrow sense, is bounded by the subserous endothoracic fascia. In a wider sense, its walls are formed by the ribs, thoracic vertebrae, sternum, and associated muscles, including the diaphragm. It is cone-shaped with the apex between the first pair of ribs and the base at the diaphragm. Rivero et al. (2005) provided a new reference for interpretation of the normal anatomy of the canine thorax imaged by computed tomography. A similar study by Cardoso et al. (2007) used a helical scanner and intravenous contrast media to visualize the lung. The endothoracic fascia (fascia endothoracica) is the areolar tissue that attaches the costal and diaphragmatic pleurae to the underlying muscles, ligaments, and bones. The endothoracic fascia is scanty where it closely attaches the costal pleura to the ribs. Dorsally and ventrally it extends into the mediastinal space and becomes the connective tissue that invests the organs and other structures that lie in the mediastinum. Cranially it passes through the thoracic inlet and is continued into the neck where it blends with the deep cervical fascia, particularly with the prevertebral portion of this fascia. Caudally it blends with the Read more […]


The lung (pulmo) () is the organ in which oxygen from the atmosphere and carbon dioxide from the blood are exchanged. The lungs serve a passive function in the mechanical act of respiration. The diaphragm, when it contracts, enlarges the pleural cavity by moving caudally. When the intercostal muscles contract and draw the ribs cranially, the size of the thoracic cavity is also increased, and thus air is drawn into the lungs because of the negative pressure that is produced. Aiding in expulsion of the air from the lungs are the abdominal muscles, which contract and force the abdominal viscera against the caudal surface of the diaphragm. The efects of age on lung function and structure were reviewed by Mauderly and Hahn (1982). In general there is considerable fibrosis and loss of function in the lungs of old dogs. Robinson (1982) summarized some functional consequences of species diferences in lung anatomy. There is no explanation for the great variation seen in lung lobation of domestic and wild mammals. The two lungs (pulmo sinister et dexter) possess many features in common. Each has a slightly concave base (basis pulmonis), which lies adjacent to the diaphragm, and an apex (apex pulmonis), which lies in the thoracic Read more […]