1. INTRODUCTION TO THE VERTABRATE BODY
I. General structure of vertebrate body A. Components 1. Head: cephalization correlated with bilateral symmetry 2. Trunk: contains coelom lined with peritoneum 3. Postanal tail: contains vertebrae and associated structures which extend posterior to the trunk 4. Appendages: no more than two sets of appendages B. Body plan described as a tube within a tube 1. Outer tube designated as somatic; comprises the body wall 2. Inner tube designated as visceral الأحشاء; composed of gut القناة الهضمية and derivatives

2. II. Vertebrate characteristics
A. Characteristics common to all vertebrates as members of the phylum Chordata
1. Notochord
2. Dorsal hollow nerve cord
3. Pharyngeal modifications: pouches, slits and arches
a. Pouches: segmentally arranged outpocketings of pharyngeal tube, which grow toward outside of organism
b. Slits: formed if pouch is met by an ingrowing groove أخدود نامي and the separating wall (closing plate) breaks down. Gill slits of squalus كلب البحرare formed this way
Arches: the tissue separating consecutive from each other
In fish the arches are known as the branchial arches or gill arches. In the human embryo, the arches are first seen during the fourth week of development. They appear as a series of outpouchings of mesoderm الأديم المتوسط on both sides of the developing pharynx. The vasculature الأوعية الدموية of the pharyngeal arches is known as the aortic arches الأقواس الأبهرية .

3. B. Characteristics which separate vertebrates from most invertebrates
1. Skeletal system
a. Vertebrae and cranium الجمجمة
b. Living endoskeleton
c. Mouth closed by raising lower jaw رفع الفك السفلي
2. Circulatory system
a. Ventral بطني heart
b. Closed blood system, i.e. capillaries as opposed to open sinuses الشعيرات الدموية بدلا من الجيوب المفتوحة
c. Erythrocytes present
3. Urinary and reproductive systems closely related
4. Two layered skin
5. Complex endocrine gland system
6. Neural crest cells خلايا العرف العصبي
Neural crest cells are a temporary group of cells that arise from the embryonic ectoderm cell layer طبقة الخلايا الأدمية الجنينية and in turn give rise to a diverse cell lineage—including melanocytes, cartilage الغضروفand bone, smooth muscle ....etc

4. III. Place of vertebrates in the animal kingdom
A. Summary of essential terms
1. Notochord: dorsally located supporting rod (bar) present in all chordates
2. Chordate: any organism which possesses a notochord at some stage of its life history
a. Protochordates والحبليات الاولية الدنيا : simple chordates which do not support vertebrae
b. Vertebrates: chordates in which additional supporting structures (vertebrae) develop around the notochord
B. Major groups of protochordates
1. Urochordates (unicates) ذيل حبليات
a. Have a notochord in tail region only
b. Possesses tough leathery tunic طبقة جلدية صلدة
c. Best known representatives are sea squirts الحقن البحرية
For more information of sea squirts:
(1) Adult
(a) Sessile filter feeders متغذيات ترشحية جالسةwith prominent بارزةpharyngeal gills
(b) Notochord with nerve cord absent
(2) Larva
(a) Free swimming
(b) Has notochord in tail; also possesses dorsal, partially hollow nerve cord
(c) Possesses pharyngeal gill slits

5. 2. Cephalochordates رأس حبليات
a. Frequently grouped under the general name amphioxus الرمحيات, which means pointed at both ends
b. Adults displays all three basic chordate characteristics
(1) Notochord: extends into head region hence the name cephalochordate
(2) Dorsal, hollow nerve cord
(3) Pharyngeal gill arches
c. Examples of vertebrates-like characteristics
(1) Segmental arrangement of muscles
(2) Pattern of circulatory system similar to that of simple vertebrates
(3) Two layered skin
(4) Filter feeders; cilia on gill arches important in obtaining food as was true of most primitive vertebrates
d. Excretory and reproductive systems invertebrate-like.

6. 3. Hemichordates نصف حبليات
a. Named for a questionable موضع شك “half notochord’’ in region of proboscis الخرطوم .
b. Sometimes listed as protochordates الحبليات الدنيا ; sometimes listed separately from chordate groups
c. Closely related to echinoderms شوكيات الجلد
d. Characteristics
(1) Questionable notochord (as indicated above)
(2) Dorsal and ventral cord; dorsal cord hollow anteriorly أمامي
(3) Pharyngeal gills slits