Anatomy

Features of external nose

Note the variation among the species in the integument of the nasal plate and surrounding muzzle area

Upper lip and ventral portion of nasal plate. Verify the extent of the philtrum varies amoung species.

This median structure should be preserved on a single side, while the other will reveal the contents of the nasal cavity on that side.  Its rostral portion (2/3) is cartilaginous, while the most caudal part of the septum is bony and develops from the perpendicular plate of the ethmoid bone, the sepatl processes of the frontal and nasal bone and the sagittal proces of the vomer.

This is the entrance into the nasal cavity and is usually much narrower than the cavity itself. In dogs it is short and tubular.  In species with eternal noses (eg humans and some other primates), the vestibule can be larger.  The passage from the vestibule into the cavity is narrow.

The smallest and most dorsal, it is a shelf-like concha that originates from the nasal bone.

More complex but shorter in the ventral portion of the canine cavity, this concha originates fro the maxilla.  Rostrally the concha is continued by the alar fold, at the ventral edge of which may be visible the opening of the nasolacrimal duct. Both conchae are covered with nasal mucosa

This complex system of scrolls occupies the caudal portion of the nasal cavity.  The scrolls are extensions of the ethmoid bone (ethmoid labyrinth or endoturbinates). The ethmoidal concha are lined with olfactory mucosa, carrying modified receptor nerve endings from the first cranial nerve whose fibers then run through the cribiform plate and into the cranial cavity.  Identify the cribriform plate and the perpendicular plate of the ethmoid

In ruminants, the largest of the ethmoidal conchae project rostrally and is sometimes referred to as a middle concha

Space dorsal to the dorsal nasal concha (upper branch of the letter E). This meatus leads to the olfactory mucosa in the ethmoidal labyrinth

Immediately ventral to the dorsal nasal concha, and dorsal to the ventral concha (middle branch of the letter E)

Ventral to the ventral concha (venral branch of the letter E)

This is the space that unites all three other meatuses, in other words the spine of the letter E.  The ventral and common meatus are the principal airways into the nasopharynx

On the roof of the oral cavity you will note the presence of transverse ridges.  Rostral to these, just causal to the central incisors, is a small eminence, the incisive papilla

On either side of the incisive papilla, these two small fissures are the opening to this. It leads through the palatine bone in the ventral meatus. During it's passage, it also communicates with the cavities containing the vomeronasal organ.

Two long thin sacs on either side of the nasal septum lines with sensory epithelium impliacted in pheromone chemoreception (flehmen reaction). The sac may be visible within the palatine if the median section was slightly off the median plane.

Poorly developed in dogs, most complex in ruminants. The frontaland maxillary sinuses are common to all domestic species. Also sphenoidal and conchal sinuses

Largest of the canine sinuses, occupies much of the rostral frontal bone, including its zygomatic processes.  Visibile on the median section dorsal to the caudal nasal cavity.  Variably divided into smaller cavities in dogs (but not cats), communicates with the ethmoidal labyrinth in the nasal cavity.  Maybe invaded by turbinates from the ethmoid (ectoturbinates).  In horses the sinus communicates indirectly with the nasal cavity via the caudal maxillary sinus.  It also invades the dorsal concha in horses, leading to the name conchofrontal sinus.  In cows and pigs the frontal sinus is large and extends over the cranial cavity and into the horn core (cows), in cows it can be divided into medial and lateral rostral sinuses and a much larger caudal sinus.

In dogs and cats, communicates freely with the nasal cavity that is usually referred to as a maxillary recess (or nasal recess). Not formed between the tables of the maxillary bone, but rather bounded by the maxilla and ethmoid.  In carnivores it lies immediately rostral to the orbits, dorsal to the roots of the last three cheek teeth, and communicates with the middle meatus.  In horses the maxillary sinus is large and divided into caudal and rostral sinuses, it communicated with the nasal cavity via the slit-like nasomaxillary opening.  The frontal and caudal maxillary sinus in the horses communicate via the frontomaillary opening.  In cows the maxillary sinus is large and communicates with the nasal cavity via a large, though dorsally places nasomaxillary opening.  It communicates with the large palatine sinus and lacrimal sinus (caudally) in this species as well.

cows, other ruminants and pigs also possess smaller sinuses within the sphenoid (rostral cranial floor) and nasal conchae (in particular the dorsal concha)

A muscular tube, and a space, at the caudal end of the oral and nasal cavities that allow communication of these cavities with the esophagus, larynx and trachea, respectively

The passage from the nasal cavity to the pharynx. Can be common or seperate

at the level of the choanae, and caudal to the oral cavity it is the oropharynx, but it is a shared space.  In the dorsal portion of the nasopharynx there is an opening that communicates with the middle ear, the pharyngeal opening (ostium) of the auditory tube

Ostium.  In the dorsal portion of the nasopharynx the opening that communicates with the middle ear. It is the opening of the auditory tube (Eustachian tube).

All mammals posses auditory tubes that connect the middle ear with the pharynx, but in horses and their cousins there exists a diverticulum of this tube known as the gutteral pouch.

• Suspends the tongue and larynx from the skull. It is a series of articulating bony rods linked to the skull (mastoid process of temporal bone) via the tympanohyoid cartilage. The bones are all paired except the basihyoid.
• In the dog the series from the skull is tympanohyoid cartilage, stylohyoid, epihyoid, ceratohyoid (or keratohyoid) and thyroihyoid, which articulates with the larynx (thyroid cartilage).  At the articulation of the ceratohyoid and thyohyoid, the left and right horns meet via the single median basihyoid

The horse hyoid does not have an epihyoid, which is fused with the stylohyoid in the adult. The latter is consequently much larger in equines. Recall that the guttural pouch wraps around the dorsal border of bone in the fresh state.  The basihyoid possess a rostrally projecting lingual process for the attachment of tongue muscles.

• The space caudal to the choanae of the nasal cavity and soft palate, and rostral to the epiglottic cartilage of the larynx, which serves as the common passage to the respiratory (ventral) and digestive (dorsal) systems.
• Commonly divided into 3 spaces: nasopharynx (at level of choanae and ostium for Eustachian tube), oropharynx (caudal to soft palate and tongue) and laryngopharynx (which surrounds the protrusion of the larynx in the pharyngeal space dorsally)

• Protective gateway to the trachea.  Also associated with vocalization. Suspended from the cranial base via the hyoid apparatus (thyrohyoid articulation) and in the fresh state rests partly between the mandibular rami in the ventral neck.
• It is mobile and shifts cranially and ventrally in swallowing to allow passage of the food bolus into the esophagus, which is dorsal to the trachea
• Three levels: from cranial to caudal, vestibule (from epiglotic cartilage to the vocal folds), the glottis, comprising vocal folds, vocal processes of the arytenoids cartilage and he narrow passage between them (rima glottidis - glottic cleft), and the infroglottic cavity, at the level of the cricoid cartilage cranial to the trachea.

Leaf-shaped, articulates with the thyroid caudally, and ventrally it is attached to the basihyoid bone.  It forms a "trap door" that swings caudally to partially cover the vestibule and prevent food/liquid to enter the larynx and trachea

Paired and irregular shaped cartilages with several processes, including 1 vocal process (ventral, attachment of the vocal ligament) 2 cuneiform process (via mucosa, links to the epiglottis to form the aryepiglottic fold) 3 muscular process (lateral, for attachment of intrinsic musculature) and 4 comiculate process which forms the dorsal/caudal border of the laryngeal entrance with its contralateral homolog. The arytenoids have a complex synovial articulation with the crocoid caudally.  Tnesion/abduction/adduction in the vocal folds is primarily determined by movements of the artenoids

"shield-shaped" cartilage formed of two lateral plates (laminae) that meet ventrally, forming the recognizable "Adam's apple" in humans. Articulates with the thyrohyoid bone, the epiglottis, and the arch portion of the cricoids caudally.

"ring-shaped" cartilage.  It is shaped like a signet ring, with a thinner arch ventrally and a thickened lamina (the signet) dorsal. Articulates with the arytenoids and the thyroid.

Superficial, from the cricoid cartilage to the thyroid lamina, it tenses the vocal folds by bringing the ventral aspects of the cricoid and thyroid together (moving the cricoid caudally along with the arytenoids)

From dorsolateral surface of cricoid lamina, diverges rostrolaterally onto muscular processes of the arytenoids. On contraction, it abducts (increases the distance) between the vocal processes on either side, hence abducting the vocal folds

from ventral/rostral cricoid arch to muscular process, it does the reverse of the c. dorsalis muscle: vocal fold adduction

In horse and dog it has two portions: the vocalis (caudal) and the ventricularis (rostral). The thyroarytenideus arises from the median thyroid and runs dorsocaudally to insert onto the muscular and vocal processes of the arytenoids. It adjusts tension in the vocal fold, to which it is parallel, and determines the size of the glottic cleft

From each arytenoid cartilage to a median raphe, it approximates the arytenoids and abducts the vocal folds.  May be difficult to identify.

The folds contain the vocal ligament and vocalis (thyroarytenoideus) muscle, overlain by larygeal mucosa.

In dogs and horses there is an additional mucosal fold in the vestibule, formed by a ventricular (or vestibular) ligament from the cuneiform proces of the arytenoids to the thyroid. This vestibular fold and the more caudal vocal fold form the boundaries of the laryngeal ventricle, a lateral outpouching of the larygeal mucosa within the vestibule lines with mucus glands.

• (cranial to heart)
• Contains the trachea and esophagus (dorsal), the cranial vena cava and end of azygos veinw, brachiocephalic trunk and left subclavian artery (first and second branches off the aoritc arch, respectively) embedded in fat, the internal thoracic artery and vein and remnants of the thymus (ventrally), depeding on the age of your specimen. 
• Lymphatic structures include the cranial mediastinal lymph nodes and the thoracic duct, the largest lymph vessel.
• Nervous structures inclue the phrenic nerve, vagus nerve (over the base of the heart), the cervicocephalic ganglion and sympathetic trunk (dorsally placed, run along the ventral surface of the neck of the ribs). At the level of the right subclavian or aortic arch (depending on which side you dissected), you may be able to see the recurrent lyngeal nerves branches off the vagus that course in a cranial direction towards the larynx

• At level of the heart
• Contains the trachea and its bifurcation into primary bronchi, the esophagus and azygous vein (right side only), aortic arch and thoracic aorta, caudal vena cava within plica vena cava, pulmonary trunk, multiple pulmonary veins and tracheobronchial lymph nodes (at the tracheal bifurcation). Ventrally this spce is occupied by the heart in its pericardium. The phrenic nerve and thoracic duct also continue their course through this space. The vagus will seperate into dorsal and ventral branches at the level of the heart.  The ventral branches from both sides will rapidly unite on the ventral surfaceof the esophagus to form the ventral vagal trunk, while the dorsal branches will unite closer to the diaphragm in the caudal mediastinum to form the dorsal vagal trunk. Both trunks innervate abdominal viscera and ass through the esophageal hiatus in the diaphragm

Caudal to heartThis is the thinnest portion of the mediastinum, connecting with the diaphragm.  It connects the esophagus, caudal vena cava (in its plica) deviated towards the right side, phrenic and vagus nerves, as well as the thoracic duct and azygos vein.