Norma Occipitalis and Normal Lateralis

Norma Occipitalis

Question 1. External occipital protuberance
Answer:

External occipital protuberance Site:

• External occipital protuberance is an median prominence in the lower part of norma occipitalis

External occipital protuberance Significance:

• External occipital protuberance marks the junction of the head and neck
• The most prominent part of it is the inion
• External occipital protuberance is easily felt at the point where the back of the neck becomes continuous with the scalp

External occipital protuberance Attachments:

• Upper part
• Gives origin to the trapezius

External occipital protuberance Lower part:

• Gives attachment to the upper end of the ligamentum nuchae.

Question 2. Superior nuchal lines
Answer:

• Superior nuchal lines are curved bony ridges passing laterally from the external occipital protuberance

Superior nuchal lines Attachments:

• Medial one-third: gives origin to trapezius
• Lateral part: provides insertion to sternocleidomastoid above and splenius capitis below

Question 3. Superciliary arch
Answer:

Superciliary arch Location & Appearance:

• It is a rounded, curved elevation situated just above the medial part of each orbit
• Prominent in males

Superciliary arch Attachments:

• Medial part: gives origin to the corrugators supercilli

Normal Lateralis

Question 1. Mastoid process.
Answer:

• The mastoid process is a nipple-like large projection from the lower part of the mastoid temporal bone
• The mastoid process forms the lateral wall of the mastoid notch

Mastoid process Location:

• Posteroinferior to the external acoustic meatus

Mastoid process Occurrence:

• During the 2nd year of life

Mastoid process Structures Present:

• Tympanomastoid fissure: on the anterior aspect of the base of mastoid process
• Mastoid foramen: at near occipitomastoid suture

Mastoid process Structures Attached:

• Sternocleidomastoid, splenius capitus & longissimus capitus inserted from before backwards on the posterior part of the lateral surface of the mastoid process
• Posterior belly of digastrics – from mastoid notch

Mastoid process Relations:

1. Tympanomastoid fissure

1. Transmits auricular branch of vagus nerve

2. Mastoid foramen – transmits

1. Emissary vein connecting the sigmoid sinus with the posterior auricular vein
2. Meningeal branch of occipital artery

Position, Connection And Branches Of Pterygopalatine Ganglion

Pterygopalatine Ganglion Situation:

Pterygopalatine Ganglion is the largest parasympathetic ganglion

Pterygopalatine Ganglion Situation Branches:

Pterygopalatine Ganglion Situation Connections:

Zygomatic arch

• The zygomatic arch is the horizontal bar

Zygomatic arch Location:

• Sympathetic root

Zygomatic arch Formation:

• Anterior 1/3rd: by the temporal process of the zygomatic bone
• Posterior 2/3rd: by the zygomatic process of the temporal bone

Zygomatic arch Parts:

• Jugal point: At the anterior end of the upper border
• Anterior & posterior root: At the posterior end
• Articular tubercle: At the junction of anterior & posterior root
• Postglenoid tubercle: Behind the articular fossa

Zygomatic arch Attachments:

Temporal fascia: Outer & inner parts of superior border of arch

Masseter: To the medial & lower border of arch

Lateral ligament of TMJ: To the tubercle of root of the arch

Pterion

• Pterion is an H-shaped suture present in the anterior part of the floor of the temporal fossa
• The pterion is a meeting point of four bones
  • Frontal
  • Parietal
  • Greater wing of sphenoid
  • Temporal

Pterion  Location:

• 4 cm above the midpoint of zygoma
• 2.5 cm behind the frontozygomatic suture

Pterion  Relations:

• Structures related to it are:
  • Middle meningeal vein
  • Anterior division of the middle meningeal artery
  • Stem of the lateral sulcus of the brain

Bones Meeting At Pterion

• Frontal
• Parietal
• Greater wing of sphenoid
• Temporal

Surgical importance of pterion

• Pterion is the thin part of skull
• In roadside accidents, the anterior division of the middle meningeal artery may be ruptured, leading to clot formation between the skull bone & the dura mater or extradural haemorrhage

Result:

• Clot compresses the motor area of the brain, leading to paralysis of the opposite side

Prevention: Use of a helmet

Mastoid process

• Mastoid Process is a nipple-like large projection from the lower part of the mastoid temporal bone
• Mastoid Process  forms the lateral wall of mastoid notch

Mastoid Process  Location:

• Posteroinferior to the external acoustic meatus

Mastoid Process  Occurrence:

• During the 2nd year of life

Structures Present:

Tympanomastoid fissure: On the anterior aspect of the base of mastoid process

Mastoid foramen: At/ near occipitomastoid suture

Mastoid Process  Structures Attached:

• Sternocleidomastoid, splenius capitus and longissimus capitus- inserted from before backwards on the posterior part of the lateral surface of the mastoid process
• Posterior belly of digastrics – from mastoid notch

 

Muscles Attached To Mastoid Process

Sternocleidomastoid, splenius capitus and longissimus capitus- inserted from before backwards on the posterior part of the lateral surface of the mastoid process

• Posterior belly of digastrics – from mastoid notch

Mastoid Groove

• The mastoid part of the temporal bone lies just behind the external acoustic meatus
• It is continuous with the squamous temporal bone
• A partially obliterated squamomastoid suture may be visible just in front of & parallel to the roughened area of muscular insertions known as the mastoid groove.

Stylomastoid Foramen Location:

• Stylomastoid Foramen is located posterior to the styloid process

Stylomastoid Foramen Structures passing through it:

• Facial nerve
• Stylomastoid branch of posterior auricular foramen

Piriform Fossa/ pṣiriform recess

• Piriform Fossa is a small cavity or pocket between the lateral walls of the pharynx on each side & upper part of the larynx
• Piriform Fossa  is also called Pyriform fossa or Pyriform sinus

Suprameatal triangle of McEwan’s

• Suprameatal triangle is a small depression present posteroinferior to the external auditory meatus.
• McEwans forms the lateral wall of the tympanic or mastoid antrum.

McEwans Boundaries:

• Superior – supramastoid crest
• Anterior – posterior superior margin of the external auditory meatus
• Posterior – vertical tangent to the posterior margin of the meatus.