Write short notes on Nasal septum, Skin, Middle ear.

# Nasal septum
It is median osteocartilaginous partition between the two halves of the nasal cavity.
Formation: On each side it is covered by mucous membrane and forms the medial wall of both cavities.

A) The bony part is formed almost entirely by -
  1. The vomar
  2. The perpendicular plate of the ethmoid

B)The cartilaginous part is formed by-
1.The septal cartilage
2. The septal processes of the inferior nasal cartilages.

C) The cuticular part is formed by fibro - fatty tissue covered by skin. the lower margin of the septum is called the columella.

The nasal septum has four borders :
1. superior
2.inferior
3.anterior
4.posterior

The nasal septum has two surfaces :
1.Right & \
2.Left


#Skin
The skin is the largest organ of the body. Histrionically skin is composed of two layers -

A) Epidermis
B) Dermis

Description of them are given below
A) Epidermis: It is the superficial layer, made up of stratified squamous keratinized epithelium.
B)Dermis : It is subdivided into two layers -
1. Papillary layer
2.Reticular layer

Functions of skin:
1. Regulation of Body temperature
2.Protection from dehydration and infection
3.Respond to temperature, pressure & pain
4.Excretion of water, salts, urea
5.Synthesis vitamin D
6.First Defensive Barrier of Immune Response


# Middle ear : It is also called the tympani cavity or tympanum.

Location: The middle ear is situated in the petrous part of the temporal bone.

Size and shape: The middle ear is shaped like a cube. its lateral and medial walls are large. it is about 15 mm diameters. the distances separating them are 6 mm near the roof, 2 mm in the center, and 4 mm near the floor.

Parts:
1.Eustachian tube
2.Ear ossicles-
            a. Malleus
            b. Incus
            c. Stapes
3.Cavity

Function: 
1.Eustachian tube
2.cavity