embryo

Question 1

Gastrulation

Answer 1

The gastrulation is the most characteristic event occurring during the third week of gestation because it forms
the three germ layers that form all the tissues and organs
of the body. The process of formation of three germ layers is called gastrulation.
The three germ layers are formed as follows.
1. First, the embryoblast differentiates into two layers:
(a) a superficial layer consisting of flat cells called
endoderm and (b) deep layer consisting of columnar cells called ectoderm. The embryo at this
stage is termed bilaminar embryonic disc.
2. Now the ectoderm forms a linear thickening in the
midline of embryonic disc called primitive streak.
The primitive streak gives rise to third layer—
the mesoderm—that lies between ectoderm and
endoderm. The embryo at this stage is called trilaminar embryonic disc. During the formation
of the three germ layers other embryonic structures
also develop. The details of formation of three germ
layers along with other embryonic structures are
described in the following text.

Question 2

second pharyngeal arch

Answer 2

Carlitage : reichet's cartilage
bones : stapes, body of hyoid
muscle : facial muscles
nerve: facial nerve
artery : stapedial artery and hyoid artery
ligaments : stylohyoid ligaments.

Question 3

first pharyngeal arch

Answer 3

cartilage : meckels’ carti
bone: malleus, incus, mandible, maxilla, zygomatic bone, temporal bone
muscle : muscles of mastication , mylohyoid , digastric ant bell
ligaments : sphenomandibular ligament
artery : maxillary artery
nerve : chorda tympani, trigeminal nerve.

Question 4

3rd pharyngeal arch

Answer 4

carti : greater conu and body of hyoid
bone : same as carti
muscle : stylopharyngens 
artery : common carotid , internal carotid
nerve : glossopharyneal nerve

Question 5

4Th PA

Answer 5

carti - cartilage of larynx
bone- same as carti
nerve - sup laryngeal nerve
artery - Aortic arch and subclavian
muscle - cricothyroid
ligament - No