The Medial Pterygoid Muscle

• This is a thick, quadrilateral muscle that also has two heads or origin.
• It embraces the inferior head of the lateral pterygoid muscle.
• It is located deep to the ramus of the mandible.

• Origin: deep head—medial surface of lateral pterygoid plate and pyramidal process of palatine bone, superficial head—tuberosity of maxilla.
• Insertion: medial surface of ramus of mandible, inferior to mandibular foramen.
• Innervation: mandibular nerve via medial pterygoid nerve.

• It helps to elevate the mandible and closes the jaws.
• Acting together, they help to protrude the mandible.
• Acting alone, it protrudes the side of the jaw.
• Acting alternately, they produce a grinding motion.

The Scalp

• The scalp consists of five layers of soft tissue.
• It extends from the superior nuchal line on the posterior aspect of the skull of the supraorbital margins.
• Laterally, the scalp extends into the temporal fossa to the level of the zygomatic arches.

Layers of the Scalp

• The scalp proper is composed of three fused layers. It is separated from the pericranium by loose connective tissue.
• Because of this potential areolar cleavage plane, the scalp is fairly mobile.
• Each letter of the word "S C A L P" serves as a memory key for one of the layers of the scalp: Skin, Connective Tissue, Aponeurosis Epicranialis, Loose Areolar Tissue and Pericranium.

Layer 1: Skin

• Hair covers the scalp in most people.
• The skin of the scalp is thin, especially in elderly people, except in the occipital region.
• The skin contains many sweat and sebaceous glands and hair follicles.
• The skin of the scalp has an abundant arterial supply and good venous and lymphatic drainage systems.

Layer 2: Connective Tissue

• This is a thick, subcutaneous layer of connective tissue and is richly vascularised and innervated.
• It attaches the skin to the third layer of the scalp.
• Fat is enclosed in lobules between the connective fibres.

Layer 3: Aponeurosis Epicranialis

• This is a strong membranous sheet that covers the superior aspect of the cranium.
• This aponeurosis is the membranous tendon of the fleshy bellies of the epicranius muscle.

• The epicranius muscle consists of four parts: two occipital bellies, occipitalis and two frontal bellies, frontalis that are connected by the epicranial aponeurosis. 

Layer 4: Loose Areolar Tissue

• This is a subaponeurotic layer or areolar or loose connective tissue.
• It is somewhat like a sponge because it contains innumerable potential spaces that are capable of being distended by fluid.
• It is this layer that allows free movement of the scalp proper, composed of layers 1-3.

Layer 5: Pericranium

• This is a dense layer of specialised connective tissue.
• The pericranium is firmly attached to the bones by connective tissue fibres called Sharpey’s fibres, however, they can be fairly easily stripped from the cranial bones of living persons, except where they are continuous with the fibrous tissues of the cranial sutures.

EPITHELIUMS

Epithelial Tissue Epithelial tissue covers surfaces, usually has a basement membrane, has little extracellular material, and has no blood vessels. A basement membrane attaches the epithelial cells to underlying tissues. Most epithelia have a free surface, which is not in contact with other cells. Epithelia are classified according to the number of cell layers and the shape of the cells.

• Epitheliums contain no blood vessels.  There is normally an underlying layer of connective tissue
• Almost all epitheliums lie on a basement membrane.The basement membrane consists of  a basal lamina and  reticular lamina. The reticular lamina is connected to the basal lamina by anchoring fibrils. The reticular lamina may be absent in which case the basement membrane consist only of a basal lamina. The basal lamina consists of a   - lamina densa in the middle (physical barrier) with a lamina lucida on both sides (+charge barrier),The basement membrane is absent in ependymal cells.The basement membrane is not continuous in sinusoidal capillaries.

• Epitheliums always line or cover something
• Epithelial cells lie close together with little intercellular space
• Epithelial cells are strongly connected to one another especially those epitheliums that are subjected to mechanical forces.  

Functions of Epithelium:

→ Simple epithelium involved with diffusion, filtration, secretion, or absorption

→ Stratified epithelium protects from abrasion

→ Squamous cells function in diffusion or filtration

Muscles of the larynx

Extrinsic muscles
    suprahyoid: raise larynx, depress mandible for swallowing
    infrahyoid: lower larynx for swallowing
    both stabilize hyoid for tongue movements

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.