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Anatomy

Intrinsic Muscles of the Tongue

The Superior Longitudinal Muscle of the Tongue

  • The muscle forms a thin layer deep to the mucous membrane on the dorsum of the tongue, running from its tip to its root.
  • It arises from the submucosal fibrous layer and the lingual septum and inserts mainly into the mucous membrane.
  • This muscle curls the tip and sides of the tongue superiorly, making the dorsum of the tongue concave.

 

The Inferior Longitudinal Muscle of the Tongue

  • This muscle consists of a narrow band close to the inferior surface of the tongue.
  • It extends from the tip to the root of the tongue.
  • Some of its fibres attach to the hyoid bone.
  • This muscle curls the tip of the tongue inferiorly, making the dorsum of the tongue convex.

 

The Transverse Muscle of the Tongue

  • This muscle lies deep to the superior longitudinal muscle.
  • It arises from the fibrous lingual septum and runs lateral to its right and left margins.
  • Its fibres are inserted into the submucosal fibrous tissue.
  • The transverse muscle narrows and increases the height of the tongue.

 

The Vertical Muscle of the Tongue

  • This muscle runs inferolaterally from the dorsum of the tongue.
  • It flattens and broadens the tongue.
  • Acting with the transverse muscle, it increases the length of the tongue.

Eye 

At week 4, two depressions are evident on each of the forebrain hemispheres.  As the anterior neural fold closes, the optic pits elongate to form the optic vesicles.  The optic vesicles remain connected to the forebrain by optic stalks. 
The invagination of the optic vesicles forms a bilayered optic cup.  The bilayered cup becomes the dual layered retina (neural and pigmented layer)
Surface ectoderm forms the lens placode, which invaginates with the optic cup.
The optic stalk is deficient ventrally to contain choroids fissure to allow blood vessels into the eye (hyaloid artery).  The artery feeds the growing lens, but will its distal portion will eventually degenerate such that the adult lens receives no hyaloid vasculature.
At the 7th week, the choroids fissure closes and walls fuse as the retinal nerve get bigger.
The anterior rim of the optic vesicles forms the retina and iris.  The iris is an outgrowth of the distal edge of the retina.
Optic vesicles induces/maintains the development of the lens vesicle, which forms the definitive lens.  Following separation of the lens vesicle from the surface ectoderm, the cornea develops in the anterior 1/5th of the eye.
The lens and retina are surrounded by mesenchyme which forms a tough connective tissue, the sclera, that is continuous with the dura mater around the optic nerve.  
Iridopupillary membrane forms to separate the anterior and posterior chambers of the eye.  The membrane breaks down to allow for the pupil
Mesenchyme surrounding the forming eye forms musculature (ciliary muscles and pupillary muscles – from somitomeres 1 and 2; innervated by CN III), supportive connective tissue elements and vasculature.


Eyelids

Formed by an outgrowth of ectoderm that is fused at its midline in the 2nd trimester, but later reopen.

The Submandibular Glands

  • Each of these U-shaped salivary glands is about the size of a thumb and lies along the body of the mandible.
  • It is partly superior and partly inferior to the posterior 1/2 of the base of the mandible.
  • It is partly superficial and partly deep to the mylohyoid muscle.
  • The submandibular duct arises from the portion of the gland that lies between the mylohyoid and hyoglossus muscle.
  • The duct passes deep and then superficial to the lingual nerve.
  • It opens by one to three orifices on a small sublingual papilla beside the lingual frenulum.
  • The submandibular gland is supplied by parasympathetic, secretomotor fibres from the submandibular ganglion (preganglionic fibres from the chorda tympani via the lingual nerve).

  • The tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
  • In each half of the tongue there are four extrinsic and four intrinsic muscles.
  • The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
  • The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.

Ligaments of the Joint

  • The fibrous capsule is thickened laterally to form the lateral (temporomandibular) ligament. It reinforces the lateral part of this capsule.
  • The base of this triangular ligament is attached to the zygomatic process of the temporal bone and the articular tubercle.
  • Its apex is fixed to the lateral side of the neck of the mandible.
  • Two other ligaments connect the mandible to the cranium but neither provides much strength.
  • The stylomandibular ligament is a thickened band of deep cervical fascia.
  • It runs from the styloid process of the temporal bone to the angle of the mandible and separates the parotid and submandibular salivary glands.
  • The sphenomandibular ligament is a long membranous band that lies medial to the joint.
  • This ligament runs from the spine of the sphenoid bone to the lingula on the medial aspect of the mandible.

The Orbital Margin

  • The frontal, maxillary and zygomatic bones contribute equally to the formation of the orbital margin.
  • The supraorbital margin is composed entirely of the frontal bone.
  • At the junction of its medial and middle thirds is the supraorbital foramen (sometimes a notch), which transmits the supraorbital nerves and vessels.
  • The lateral orbital margin is formed almost entirely of the frontal process of the zygomatic bone.
  • The infraorbital margin is formed by the zygomatic bone laterally and the maxilla medially.
  • The medial orbital margin is formed superiorly by the frontal bone and inferiorly by the lacrimal crest of the frontal process of the maxilla.
  • This margin is distinct in its inferior half only.

Innervation of the Pharynx

  • The motor and most of the sensory supply of the pharynx is derived from the pharyngeal plexus of nerves on the surface of the pharynx.
  • The plexus is formed by pharyngeal branches of the vagus (CN X) and glossopharyngeal (CN IX) nerves, and by sympathetic branches for the superior cervical ganglion.
  • The motor fibres in the pharyngeal plexus are derived from the cranial root of accessory nerve (CN XI), and are carried by the vagus nerve to all muscles of the pharynx and soft palate.
  • The exceptions are stylopharyngeus (supplied by CN IX) and the tensor veli palatini (supplied by CN V3).

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