The cartilaginous neurocranium (chondro-cranium) of the base of the skull is formed by fusion and ossification of number of separate cartilages along the median plate.

Viscerocranium arises primarily from the first two pharynge arches.

Appendicular system: The pectoral and pelvic girdles and the limbs comprise the appendicular system.

Except for the clavicle, most bones of the system are end chondral. The limbs begin as mesenchymal buds with an apical ectodermal ridge covering, which exerts an inductive influence over the mesen-chyme.

Bone formation occurs by ossification of hyaline cartilage models.

The process begins at the end of the embryonic period in the primary ossification centers, which are located in the shaft, or diaphysis, of the long bones. At the epiphyses, or bone extremities, ossification begins shortly after birth.

The cartilage that remains between the diaphysis and the epiphyses of a long bone is known as the epiphysial plate. It is the site of growth of long bones until they attain their final size and the epiphysial plate disappears.

Vertebral column.

During the fourth week, sclerotome cells migrate medially to surround the spinal cord and notochord. After proliferation of the caudal portion of the sclerotomes, the vertebrae are formed, each consisting of the caudal part of one sclerotome and cephalic part of the next.

While the notochord persists in the areas of the vertebral bod ies, it degenerates between them, forming the nucleus pulposus. The latter, together with surrounding circular fibers of the annulus fibrosis, forms the intervertebral disc.

New words

skeletal – скелетный

mesoderm – мезодерма

neural – нервный

crest – гребень

cartilage – хрящ

fibroblasts – фибробласты

chondroblasts – хондробласты

osteoblasts – остеобласты

paraxial – параксиальный

which – который

may – мочь, может

flat – плоский

bone – кость

to provide – снабжать

protection – защита

long – длинный

Запомните следующее застывшее словосочетание.

In front

Запомните следующие конструкции, требующие неопределенного артикля.

I have a…

Не has a…

I see a…

I am a…

He is a.

She is a.

This is a.

That is a.

It is a…

There is a.

Вставьте артикль, где необходимо.

1. We have… big dog… dog is very clever.

2. My friend has… very good computer.

3. This… boy is big. He is… student.

4. There is… very big piano in. hall.

5. This is. tree and that is not… tree. It's. bush.

6. I am… boy. I am… pupil. I learn at… school.

7. My sister is at… work. She is… secretary. She works at… large office.

8. This is… very difficult question. I don't know. answer to it.

9. Do you see… little girl with… big ball in her… hands? She is… pupil of our… school.

10. There was… beautiful flower in this… vase yesterday. Where is … flower now?

Answer the questions.

1. Where the components of the skeletal system are derived from?

2. What do mesenchymal cells differentiate into?

3. What produces connective tissue, cartilage, and bone tissue?

4. What does the splanch nic mesoderm give rise?

5. What does the integument consist of?

6. What is the skeletal system developed from?