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Introduction to Embryological Development

Embryological Development
Laryngeal mucosa develops from the endoderm of the cephalic part of foregut. Laryngeal cartilages and muscles develop from the mesenchyme. Development of other structures is as follow:
  1. Epiglottis                                               Hypobranchial eminence
  2. Upper part of thyroid cartilage                  4th arch
  3. Lower part of thyroid cartilage
  4. Cricoid cartilage
  1. Corniculate cartilage                               6th arch
  2. Cuneiform cartilage                                            
  3. Intrinsic muscles of larynx
  1. Upper part of body of hyoid bone
  2. Lesser cornua of hyoid bone                  2nd arch
  3. Stylohyoid ligament
  • Lower part of body of hyoid bone and greater cornua - 3rd arch

Nerve Supply
  1. Superior laryngeal nerve, a branch of vagus, is 4th arch nerve and supplies cricothyroid and constrictors of pharynx.
  2. Recurrent laryngeal nerve is 6th arch nerve and Supplies all the intrinsic muscles of larynx except cricothyroid.
The larynx is a tubular structure that has 3 paired and 3 unpaired cartilages.
  1. Unpaired: Thyroid, Cricoid and Epiglottis
  2. Paired: Arytenoids, Cuneiform (of Wrisberg) and Corniculate(of Santorini)
Dimensions (Larynx)
  Male Female
* Antero-posterior diameter: 36 mm 26mm
* Transverse: 43mm 41mm
* Length: 44mm 36mm


Extra Edge

(i) The AP length of vocal cord or gloltis is as follows:
a. Male: 24 - 26 mm            
b.  Female: 16 - 17 mm
(ii) However, the AP length of larynx will increase by 10 -12 mm & hence length of larynx in as follows.
a. Male : 36 mm         
b.  Female : 26 mm

  1. Angle of the thyroid cartilage at birth:    
    1. Males = 110 degree
    2. Females = 120 degree                                             
    3. The angle till puberty.
    4. Males – 90o; Females – 120o
  2. Level of the larynx:
    1. At birth : Till C5
    2. By 5yrs : Till C6
    3. 15-20 yrs  : Till C7
  3. Descent of the larynx continues throughout life
  4. Vocal cord length:
    1. Infants  : 6-8mm.
    2. Adults Males : 17-23 mm
    3. Adults Females : 12-17
  5. Ossification of the various laryngeal cartilages:
    1. Hyoid 2yrs     
    2. Thyroid &  Cricoid Early 20’s   
    3. Arytenoid late 30’s
    4. vocal process DO NOT ossify
    5. No ossification occurs in the cuneiform or the corniculate.
  6. Laryngeal Cartilages:
Thyroid Cartilage
  1. Shield like cartilage (hyaline)
  2. Angle of fusion of the lamina.
    1. 90 degree : male
    2. 120 degree : female
  3. Oblique line extends from super thyroid tubercle to inferior thyroid tubercle and gives attachment to 3 muscles:  Thyrohyoid/ Sternothyroid and Inferior constrictor
Cricoid Cartilage (hyaline cartilage)
Fig: Laryngeal framework

Fig: Sagittal section of larynx showing cricovocal and quadrangular membranes
and boundaries of the pre-epiglottic space.

Fig: Coronal sectional section of larynx. Lower free edge of the quadrangular membrane lies in the false cord while upper free edge of te cricovocal membrane forms the vocal ligament. Note formation of conus elasticus by the cricovocal membranes of two sides.

Fig: Intrinsic muscles of larynx as seen on lateral view

Fig: Laryngeal inlet and intrinsic muscles of larynx as seen from behind

Fig: Rima glottidis. Note anterior 2/3 of vocal cord is membranous
and posterior 1/3 cartilaginous

Parts : Anterior arch
Posterior lamina.
Cricoarytenoid joint : Synovial joint
  1. Epiglottis
    Elastic fibro cartilage.
    Pre epiglottic space: Anteriorly : thyrohyoid membranespace of Boyer)        
    Posperior : infrahyoid part of the epiglottis.
    Superior : hyoepiglottic ligament.
    Paraglottic space : Continous medially with the pre epiglottic space.
    Laterally : Thyroid cartilage
    Medially : quadrangular membrane and conus elasticus.
    Posteriorly : ant. reflection of pyriform sinus.
  2. Arytenoid Cartilage
    3-sided pyramid
    Has a vocal process : Vocal folds attached
    Muscular process : Posterior cricoarytenoid.
                                   Lateral cricoarytenoid.
    Apex : articulates with corniculate
    Corniculate and cuneiform are elastic fibro cartilages.

Extra Edge. Elastic fibrocartilage is seen in pinna, epiglottis, corniculate, cuneiform cartilages and apices of the arytenoid cartilages. It does not undergo calcification. Hyaline cartilage is seen in thyroid, cricoid, and greater part of arytenoid cartilages. It undergoes calcification.



Extra Edge. Hidden areas of the larynx include infrahyoid epiglottis,
anterior commissure, subglottis, ventricle and apex of pyriform fossa.
Extra Edge. Larynx has three important spaces: pre-epiglottic, paraglottic and Reinke’s. The first two are important because they are invaded by carcinoma arising in the laryngeal mucosa. Reinke’s space is often affected by oedema and causes polypoid degeneration of vocal cords. This is called as Reinke’s oedema, It is discussed later.
  1. Extrinsic membranes
    1. Thyrohyoid
    2. Cricotracheal
    3. Hyoepiglottic
  1. Thyrohyoid membrane
    Above: upper border of the posterior surface of the body of hyoid bone and greater cornu.
    Below : upper border of the thyrohyoid cartilage-
    Structures piercing :
    Superior laryngeal vessels
    Internal branch of superior laryngeal nerve
    1. Intrinsic
      Quadrangular membrane: is a fibroelastic, lies deep to the mucosa of the aryepiglottic fold. Its lower border forms the vestibular ligament which lies in the false vocal cord.
      Cricovocal Membrane: a fibroelastic membrane. Upper border forms the vocal ligament. Anteriorly meets with its fellow to form the conus elasticus(laryngeal foreign bodies get stuck here sometimes)
    2. Inlet of the larynx:
      1. Superiorly :Free edge of the epiglottis
      2. Sides :Aryepiglottic folds
      3. Posteriorly : Mucous membrane over the inter-arytenoid fold.
  • Vestibule: From the laryngeal inlet to the vestibular fold
  • Ventricle/sinus of the larynx: is an elliptical space which lies between the vestibular and the folds.
  • Saccule: Is a diverticulum of mucus membrane
    It starts at the anterior part of the ventricular cavity and extends between the vestibular folds and inner aspect of the lamina of the thyroid cartilage.
  1. Vocal folds:
    Extents: are two fold like structures which extends from the middle of the angle of the thyroid cartilage to the vocal process of the arytenoids.

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