This chapter starts with the development of the vertebral column. The dorsal portion of an embryo during the course of the 4th week is shown in transversal section. The neural tube, somite, notochord, dorsal aorta, intersegmental arteries and ectoderm are shown. Then, the entire dorsal portion of the embryo is tilted back to show all of these structures in 3D. During this movement, the ectoderm is erased from the diagram. Beside the neural tube, the notochord, dorsal aorta, four intersegmental arteries and four somites composed of dermomyotomes and sclerotomes are shown. In the next sequence, the aorta with intersegmental arteries is removed except for a short segment of the lowest intersegmental arteries. Two theories of development of the vertebral columns are animated in a 4-week-old embryo.

In the first theory, the cranial portions of the somites migrate cranially, while caudal portions migrate caudally to surround the notochord. Thus, according to the first theory, the cartilagineous primordia of the vertebrae form from the caudal portion of one somite and the cranial portion of the next somite. The next sequence, in a 6-week-old embryo, animates the growth of the vertebral bodies, indicating their composition. The evolution of the myotomes and their innervation are also shown.

During the next two weeks, the transversal processes are animated as well as notochordal regression within the bodies of the vertebrae. The transformation of the notochord into the nuclei pulposi within the annuli fibrosi of the intervertebral discs is shown. Evolution of muscles and their innervation are also demonstrated. In addition, movements of the vertebral column such as compression, lateral flexion, and ventral and dorsal flexion are animated.

The second theory of the development of the vertebral column, called the resegmentation concept, is animated in profile. The horizontal migration of the sclerotome cells toward the notochord is shown with the evolution of the muscles in an embryo during the course of the 4th week. The formation of the sclerotomes around the notochord is shown in a 4-week-old embryo. Then, in a 6-week-old embryo, the resegmentation of the sclerotomes gives rise to the vertebral bodies. The definitive constitution of the vertebral bodies, nuclei pulposi and annuli fibrosi as well as the evolution of the nerves, future intervertebral discs and muscles is animated in an 8-week-old fetus.

The next series of sequences animate the development of the vertebrae and ribs viewed in horizontal section. The first diagram shows the thoracic region of a 4-week-old embryo with a sectioned neural tube, neural crests, notochord and somites, each of which is composed of a dermatome, myotome, and sclerotome. The next sequence animates the migration of the sclerotome cells toward the notochord to constitute the precartilaginous centre of the vertebrae in a 5-week-old embryo. In parallel, the spreading of the dermatome cells under the overlying ectoderm to from the dermis and hypodemis of the future skin is also animated. Then, the future skin and myotome are erased from the diagram. During the next week, the vertebral body, neural arches and ribs grow. The dorsal root ganglia and anterior and posterior roots develop at the same time. From the 6th to 10th week, the endochondral ossification areas spread. This process of ossification is followed through two sequences up to the 25th year of life.

The following malformations of the vertebral column are described but not animated: hemivertebrae, vertebral bar, block vertebrae, sagittal cleft vertebrae, congenital brevicollis, rachischisis, spina bifida occulta, meningomyocele, and meningocele. The last four malformations are animated under the Central Nervous System.

The next chapter animates the development of the sternum in several sequences. The first diagram of a 6-week-old embryo shows the sternal bands in front of the ribs. Over the course of the next week, the sternal bands lengthen, transform into the sternal bars and connect with the ribs. In the next sequence, the sternal bars fuse with the interclavicular blastema in an approximately 8-week-old fetus. Two weeks later, the manubrium, corpus and xiphoid process occur. Ossification of the sternum is shown from the 4th month to the 12th year, the.

Malformation of the cleft sternum is illustrated but not animated. This malformation is animated under Body Cavities.

Several sequences animate the chapter on skull development. First, successive diagrams summarize the subdivision of the skull (neurocranium, viscerocranium) and the neurocranium into the membranous neurocranium and chondrocranium along with their derivatives.

The animation starts with the development of the chodrocranium. The head of a 6-week-old embryo is cut on the mediosagittal plane and observed under low magnification. The diagram contains more than 15 legends covering cartilaginous pieces of the skull. The vault of the skull is removed, and the basis of the skull is observed from above under moderate magnification. All cartilages of the future basis of the skull are shown along with the cranial nerves. The diagram contains more than 25 legends. Between the 6th week old and 3rd month, the cartilaginous pieces and nerves gradually approach. This continues from 3rd month to adulthood. The development of the ethmoid, sphenoid, petrous and occipital bone is shown with some areas of the former membranous ossification.

Beginning with a 6-week-old embryo, the development of the chodrocranium, neurocranium and viscerocranium is animated in side view. The diagram details the composition of the chodrocranium, including the position of the notochord. In the next sequence, the chodrocranium is rotated and shown in profile to also illustrate the following structures situated caudally from the basis of the skull: nasal cartilage, trabeculae cranii, ala orbitalis, hypophyseal cartilage, ala temporalis, periotic capsule, occipital sclerotomes and notochord. The side view reveals the cartilages of the neck (Meckel's and Reichert's cartilages as well as hyoid, thyroid cricoid and tracheal rings) in a 6-week-old embryo.

An 8-week-old fetus shows the growth and evolution of the above-mentioned structures along with the development of the squama occipitalis, tympanic ossicles, styloid process, hyoid bone, and laryngeal and tracheal cartilages. From weeks 8 to 20, the flat bone of the skull develops according to the mechanism of the membranous or direct bone formation. On the diagram, the mechanisms of bone formation are indicated in different frames.

Special sequences show the evolutionary history and development of the temporomandibular joint. These sequences start with a diagram showing the primary temporomandibular joint in fish. The next three sequences illustrate changes in this joint for amphibia, sauropsida, and mammals. In the latter, the development of the secondary temporomandibular joint is animated.

From the following malformations, only craniosynostosis (scaphocephaly, acrocephaly and plagiocephaly) is shown in the present animation; anencephaly and cranioschisis (meningocele, meningoencephalocele and meningohydrencephalocele) are animated in the Central Nervous System.

The next chapter deals with the development of the limb skeleton beginning with the upper limb. The first diagram shows a 24-day-old embryo in 3D. Neuropores, 1st and 2nd pharyngeal arches, somites, allantois, vitelline duct, connecting stalk and pericardial bulge are shown. Two days later, the upper limb buds appear and continue to grow during the next sequence, which ends with an approximately 30-day-old embryo. The apical ectodermal ridges appear at the tip of both the upper and lower limbs. The left upper limb is framed and isolated; the entire body of the embryo is erased. The next sequences animate the growth of the upper limb and the differentiation of its anatomical structure from the 34th to 38th day. The zones of apoptosis are shown with the digital plate, carpal region, ulna, radius, humerus and scapula. In an 8-week-old fetus, the apoptotic individualization of fingers is illustrated along with the development of the carpus.

The chapter on the development of the limb skeleton continues with the development of the lower limb. The first diagram represents an approximately 28-day-old embryo whose lower limbs grow on the 30th day. The lower left limb remains on the screen, but all other structures are erased. The diagram shows the apical ectodemal ridge, scleroblastema of the femur and acetabulum, and sclerotomes of the sacral vetrebrae, mesenchyme and ectoderm. The next four sequences cover the period up to an approximately 12-week-old fetus, depicting the growth of the lower limb. The development of the entire lower limb skeleton, including the sacrum and apoptotic separation of toes, is shown.

The next sequences animate the development of a synovial joint (diarthrosis). In an approximately 6-week-old embryo, a mesenchymal primordium of a finger lined by the epiderm is shown. The following sequence depicts the development of a synovial joint between the 2nd and 3rd phalanx. Over the course of the 7th week, the finger grows, and axial condensation occurs within the mesenchymal tissue. In an approximately 7-week-old embryo, three chondrific centers (scleroblastemata) appear within the axial condensation. During the 8th week, precartilage is surrounded by the future perichondrium, and the finger continues to grow. In an approximately 8-week-old fetus, the precartilage transforms into pieces of hyaline cartilage, which are enclosed by the perichondrium.(The histologic difference between precartilage and cartilage is not discussed. See Endochondral Ossification.)

The area between the 2nd and 3rd phalanx is delimited and magnified. On the diagram, the structure of the hyaline cartilage is described briefly along with the dense connective tissue between the two cartilagineous pieces. From the 8th week to the 3^rd month, necrosis of the dense connective tissue occurs in the form of vacuoles. One month later, the vacuoles fuse to form the synovial cavity. Simultaneously, the epiphyses enlarge to form the articular cartilages; the fibrous layer (i.e. continuation of the perichondrium) and synovial membrane form the articular capsule. Together, the articular cartilages and articular capsule form the synovial joint.

The next sequences animate the development of menisci and intra-articular ligaments through the future knee joint of an approximately 8-week-old fetus. The diagram presents hyaline cartilage pieces for the future femur, tibia and fibula. From this stage up to the newborn, the synovial cavity forms along with cruciate ligaments, menisci and articular capsule. In addition, the epiphyses become enlarged, and the femoral and tibial ossification centres appear.

As malformations of the limb skeleton, amelia, meromelia, phocomelia, sirenomelia, hemimelia, clubfoot (talipes), and others are illustrated but not animated. Polydactyly, syndactyly and cleft foot are animated.

(This animation is essential for students of medicine, veterinary medicine, stomatology and biology as well as for departments of anatomy, histology, embryology, and cell biology; it is also recommended for departments and clinics of pathology, pediatrics, orthopedics, kinesitherapy, and maxillofacial, orthopedic, and plastic surgery.)