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Summary …………………………………………………….…………………………………………..
Summary
The present study was carried out on thirty five apparently healthy
adult Balady rabbits of different sexes. Thirty rabbits were used for gross
anatomical studies of the larynx. Other five adult rabbits were used for
the histological study to confirm some anatomical findings.
The present study revealed that the larynx in the Balady rabbit is
short tubular box like organ wide at its middle than at either ends due to
the presence of large thyroid cartilage. The larynx extends from the
junction between the head and neck to the level of the first and second
cervical vertebrae. The average length of the larynx in the examined
animals is about 2 cm while the average width is nearly 1.1cm.
The cartilaginous framework of the larynx consists of three single
cartilages namely; the cricoid, thyroid and epiglottic cartilages and three
paired cartilages namely; the arytenoid, corniculate and cuneiform
cartilages.
The cricoid cartilage is signet-ring shaped composed of dorsal
quadrilateral lamina and ventrolateral arch. It surrounds the first
cartilaginous ring of the trachea. The rostral margin of the cricoid arch is
nearly straight but has caudoventral direction, while its caudal margin is
concavo-convex from above downward.
The thyroid cartilage is the largest of the laryngeal cartilages and
is gutter shaped. It consists of two quadrilateral laminae which united
ventrally in the midline to form the body of the thyroid cartilage. The
laryngeal prominence and the caudal thyroid notch are absent. The lateral
surface of the thyroid lamina presents transverse and longitudinal ridges.
The transverse ridge divides the lateral surface of the thyroid lamina into
dorsal and lateral parts. The rostral and caudal thyroid cornua are
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present. The thyroid foramen present dorsal to the rostral end of the
transverse ridge.
The epiglottic cartilage is leaf like with rounded and slightly
notched apex. It presents an apex, base, two surfaces and two borders.
The arytenoid cartilages are small irregular triangular in shape
situated rostral to the rostral border of the cricoid lamina. The corniculate
cartilages are thin flat elastic cartilaginous pieces attached to the apices
of the arytenoid cartilages.
The cuneiform cartilages are very small bar like cartilaginous
processes directed caudodorsally and they are attached to the base of
the epiglottis.
The cricothyroid and cricoarytenoid articulations are synovial
joints while the arycorniculate articulation as well as the articulation
between the epiglottic and cuneiform cartilages are cartilaginous in type.
The thyrohyoid joint is absent where the rostral cornu of the thyroid
cartilage and thyrohyoid bone are connected by the thyrohyoid ligament.
The mucous membrane covering the epiglottic cartilage is
reflected from its lateral borders caudodorsally to attach with the
corniculate process and the rostral border of the arytenoid cartilage by
the aryepiglottic fold which takes the shape of inverted triangle.
The cricotracheal ligament is short elastic membrane connects the
caudal margin of the cricoid cartilage with rostral margin of the first ring
of the trachea. The thyrohyoid membrane is an elastic ligament extends
from the basihyoid and thyrohyoid bones to the rostral margin and rostral
cornua of the thyroid cartilage. The hyoepiglottic ligament extends from
the upper surface of the basihyoid bone to the basal part of the lingual
surface of the epiglottic cartilage.
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The cricothyroid ligament is an elastic relatively triangular strong
ligament connects the rostral margin of the cricoid arch with the caudal
margin of the thyroid laminae. It consists of ventral portion and two
lateral portions. The cricoarytenoid ligament is a very short and weak
ligament stretches between the rostral margin of the cricoid lamina to the
dorsal border of the arytenoid cartilage. The thyroepiglottic ligament is a
short ligament present between the base of the epiglottis and the upper
surface of the body of the thyroid cartilage.
The vocal ligament extends from the upper surface of the caudal
end of the body of the thyroid cartilage to the vocal process of the
arytenoid cartilage and it has vertical direction. The transverse arytenoid
ligament could not be identified by the naked eye but it is represented
microscopically by collagen fibers connecting the apices of the two
arytenoid cartilages with each other.
The sternothyroid muscle is a long muscle originates from the
upper surface of the rostral half of the sternum in common with the
sternohyoid muscle and inserts in the transverse and longitudinal ridges
on the lateral surface the thyroid lamina. The thyrohyoid muscle is
a relatively short muscle originates from the site of insertion of the
sternothyroid muscle and inserts on the thyrohyoid bone. The
hyoepiglottic muscle is a narrow cylindrical muscle originates from the
upper surface of the basihyoid bone and inserts in the basal part of the
lingual surface of the epiglottic cartilage.
The cricothyroid muscle is nearly quadrilateral muscle arises
from the longitudinal groove on the cricoid arch and the adjacent part of
the lateral surface of the cricoid arch and directed craniodorsally to be
inserted on the caudal border and the adjacent part of the thyroid lamina.
The dorsal cricoarytenoid muscle is a small quadrilateral muscle covers
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the dorsal surface of the cricoid lamina, while the lateral cricoarytenoid
muscle arises from the proximal third of the rostral border of the cricoid
arch and inserts on the base of the arytenoid cartilage.
The transverse arytenoid muscle is a small muscle consists of two
lateral portions united in the midline at the base of the corniculate
cartilages. The M. thyroarytenoideus is undivided triangular muscle arises
from the upper surface of the body of the thyroid cartilage and inserts in
the base of the arytenoid cartilage.
The laryngeal mucous membrane continues rostrally with that of
the laryngopharynx and caudally with that of the trachea.
The vestibular fold is very thin as it is only membranous comprises
neither ligament nor muscle. It is formed by reflection of the mucous
membrane of the base of the epiglottis close to the cuneiform cartilage to
the base of the corniculate process.
The vocal fold is prominent and relatively swollen formed by the
vocal ligament, the mucous membrane covering it and the underlying part
of the thyroarytenoid muscle.
The laryngeal cavity is continuous rostrally with the cavity of the
laryngopharynx at the Aditus laryngis and caudally with the trachea at
the laryngeal outlet. The Cavum laryngis can be divided into three
compartments; the vestibulum laryngis, Glottis and Cavum infraglotticum
from before backward. The laryngeal vestibule extends from the
laryngeal opening till the vocal fold. The glottis is the middle
compartment and is the narrowest chamber between the two vocal folds
comprises Pars intermembranacea and Pars intercartilaginea. The
infraglottic cavity is the caudal compartment extended from the caudal
border of the vocal fold to the caudal margin of the cricoid cartilage and
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it is wider in diameter than the glottis. The laryngeal ventricles and
saccules are absent.
The laryngeal mucosa is lined by stratified squamous non
keratinized epithelium extending from the laryngeal vestibule to the
caudal edge of the vocal fold.While, the remainder of the epithelium is
respiratory epithelium which is pseudostratified columnar ciliated
epithelium with goblet cells. A transitional zone of stratified cuboidal to
stratified columnar epithelium occurred between both types of the
epithelium.
No taste buds can be detected within the area covered by the
stratified squamous epithelium. Also, no lymphatic nodules can be
demonstrated within the propria submucosa of the Balady rabbit larynx.
The cricoid, the main part of the arytenoid and thyroid cartilages are
hyaline, while the epiglottis with its cuneiform process and the
corniculate and vocal processes of the arytenoid cartilages are elastic
cartilages. The laryngeal glands are mainly mixed glands as sometimes
are mucous or serous glands. These glands are observed mainly at the
lingual surface of the epiglottis.
The margin of the vocal cord is free from the glands but the base
of the cord contains gland. The laryngeal muscles are of skeletal type.
The larynx in the Balady rabbit receives its main arterial blood
supply from the A. laryngea cranialis, R. laryngeus caudalis, R.
cricothyroideus and Rr. perihyoidei. The origin, course and mode of
distribution of the laryngeal arteries were studied.
The larynx is innervated by the cranial and caudal laryngeal
nerves which are branches from the N. vagus. The cranial laryngeal nerve
is divided into external and internal branches. The R. externus innervates
the cricothyroid muscle. The R. internus supplies the epiglottis,
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corniculate cartilage and the aryepiglottic fold and also ramifies in the
mucous membrane of the larynx. The caudal laryngeal nerve innervates
all the intrinsic laryngeal muscles except the cricothyroid muscle and also
it ramifies in the mucous membrane of the larynx.
The obtained results are discussed with those of the rabbits and
other animals.
The nomenclature used is adopted according to Electronic Edition
of Nomina Anatomica Veterinaria (2005).
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