REPTILES-JACOBSONS ORGAN

Jacobsons Organs (Sense Organs) In Reptiles:

In Reptiles the “organs of Jacobson” are well developed sac like chambers. They lie below the nasal cavity and above the buccal cavity. Each organ is a blind pocket. It is lined with olfactory epithelium. Each sac opens into the buccal cavity through narrow duct.

The Jacobsons organs will develop as an outgrowth from the nasal cavity. The Jacobson’s organ get nerves from the oactory nerve and a branch from the trigeminal nerve. These organs test the smell of the food when it is taken into the buccal cavity.

CARAPACE-PLASTRON

Carapace and Plastron:

The trunk of chelonia is enclosed by Shell which has two parts, a dorsal carapace and a flat ventral plastron, joined on the sides. This is called tortoise shell.

 

 

 

 

 

 

Carapace:

It includes a median serieiof 8 small neural plates. On their right and left lateral sides 8 costal plates are present. On the margins of small 1.1 marginal plates are present. The neural plates are fused with the neural spines of 2nd to 9th trunk vertebrae. The costal plates are fused with ribs of the 2nd to 9th trunk vertebrae. At the anterior end a nuchal plate present and at the hind end a pygal plate is present.

Plastron:

It includes median entoplastron which êorresponds to the interclavicle and a four paired plates known as 1) epiplastra which lie in front of the entoplastron 2) hypoplastron 3) hyoplastra and 4) xiphiplasfronananged below the endoplastron serially.

This shell covers and protects the body of a chelonian. When the animal is disturbed the entire animal withdraws into the shell.

SNAKE- BITE MECHANISM

Biting Mechanism of a snake

Snakes consisting Poison-Apparatus By the contraction of digastric muscles in Poison-Apparatus in snake the mouth is opened. Then the lower jaw moves forward. The sphenopterygoid muscles contract which results in the forward movement of pterygoid which brings rotation of maxilla, results the fang is raised and becomes directed forward.

The contraction of the digastric muscle will squeeze of poison gland. This makes the poison to come out of the poison gland and flows into the enemies body.

Snake-Poison-Apparatus

Poison - Apparatus of a Snake:

It has a pair of poison glands, or ducts and a pair of fangs. The poison glands are present on the upper jaw. The poison glands are the superior labial glands. Each poison gland is sac like. It gives a duct The duct passes along the side of the upper jaw. It opens into the groove of the fang. Fangs are of two types.

1) Open type (Ex: Cobra), 2) Closed type (Ex: Viper)

In open type the poison groove is present in cased type the Poison groove forms a canal with two openings at both ends.

Muscles associated with poison apparatus:

Three types of muscles are present.

1) Digastric,

2)Spheno- pterygoid,

3)anterior and posterior temporalis.

Digastric muscle is attached to the squamosal of the skull and articulates with the lower jaw. Sphenopterygoid is attached to the sphenoidal region and to the dorsal surface of the pterygoid. Anterior and posterior temporalis muscles are attached to the side walls of the cranium and the lower jaw. 

REPTILES-CLASSIFICATION

CLASSIFICATION OF REPTILES
based on characters Reptiles is divided into Four sub class
 
1)ANAPSIDA
2) PARAPSIDA
3) DIAPSIDA
4) SYNAPSIDA.
 
 
 
 
Subclass -Anapsida:
1) The skull of Reptiles are made by solid roof.
2) In these Reptiles temporal vacuities are absent in the skull.
3) In these Reptiles the quadrate is articulated with Otic bone.
4) Limbs are strong.
1) Carapace and plastron will form the body covering.
This subclass is divided into two orders.
1) Cotylosauria 2) Chelonia.
Order: Cotylosauria:
1) These Reptiles are extinct.
2) They show complete cranial roof.
3) Pelvic girdle is flat.
4) In these Reptiles Jaws and teeth are poorly developed.
These Reptiles resemble with Labyrinthodont Amphibians.
They became extinct in the triassic period of Mesozoic era.
Ex Seymauria and Lepidosaurus.
Order: Chelonia:
This order includes Turtles and Tortoises.
1) These are Terrestrial or aquatic.
2) Body is covered by shell containing dorsal carapace and ventral plastron.
3) Neck, limbs and tail are covered with scales.
4) They show 4 limbs. pentadactyle are, modified into paddles in aquatic forms.
5) Jaws without teeth.
6) Jaws show horny sheaths,
7) Quadrate is immovably articulate.
8) Nasal opening is single.
9) Unpaired copulatory organs are present.
10) Cloacal opening is longitudinal.
11) These are Oviparous.
Ex :.Thonyx (Soft river terrapin), Testudo (Land tortoise). Chelone (Turtle).
Sub class : Parapsida.
1) This group includes extinct forms.
2) Those forms lived from Triasslac period to cretaceous period.
3) Their skull shows one pair of temporal vacuities. They are supratemporal fossae
Ex, lchthyosaurus, plesiosaurus. -
Subclass 3 : Diapsida.
1) In these Reptiles skull shows two temporal vacuities.
2) Modification of typical diapsid condition is common among these members.
This subclass is divided into two super orders Lëpidosauria and Archosauria.
Super Order: Lepldoauiia
1) These are primitive reptiles.
2) Teeth are present on the palate jaw margins. They are not present in Sockets.
This super order includes two living orders.
1) Rhynchocephalia 2) Squamata.
Order: Rhinchocephaiia :-
1) Teeth are acrodont.
2) The skull shows two vacuities.
3) Quadrate bone is immovable.
4) An epipterygoid bone is present
5) Vertebrae are Amphicoelous..
6) Copulatory organs are absent in this order.
Ex Sphenodon (Newzeàland)
Order : Squamata
This includes Snakes & Lizards.
1) Their body is covered by epidermal scales.
2) Single supra temporaI vacuity is seen in lizards and temporal vacuity Is absent In snakes.
3) Teeth are pleurodont.
4) Usually procoelous vertebrae are present.
5) Transverse cloacal opening is piesent.
6) Male shows a pair of eversible copulatory organs, useful for
copulation.
This is divided into two suborders.
Sub order: 1) Lacertilia.
1) These are terrestrial, arboreal or burrowing forms.
2) limbs &re pentadactyl and are usually present.
3) Sternum is present.
4) Eyelids are movable.
5) Tympanum is present.
Ex : Calotes, Chamaeleon, Draco, Varanus, Gecko. 
Sub order: Ophidia.
This sub order includes snakes.
1) They are terrestrial or aquatic, or arboreal or burrowing forms.
2) Temporal vacuities are absent.
3) limbs and limb girdles are absent.
4) Sternum is absent.
5) Eyelids are absent.
6) Tympanum is absent.
7) Tongue is bifid.
Ex Python , Lycodon, Naja naja, Hydrophis, Viper.
Super order Archosauria
This includes advanced reptiles.
1) Teeth are on jaw margins and are set in muscular sockets.
This super order includes a single living order Crocodilia.
Order -Crocodilia:
1. These are fresh water and predatory forms.
2. Body is covered by an exoskeleton made by horny’ scales & scute.
3. Teeth are thecodont.
4. Quadrate is immovable.
5. Vertebrae are procoelous.
6. Spongy lungs are seen.
7. Longitudinal cloacal opening is present.
Ex Crocodilus, Alligator, Gavialis
Sub Class: SYNAPSIDA.
1. This group includes all extinct forms.
2. They lived from carboniferous to permen period.
3. Their skull shows one pair ot Vacuities. These vacuities are infratemporal fossal.
Ex: Dimetrodon, Cynognathus.

REPTILES - GENERAL CHARACTERS

REPTILES-INTRODUCTION

In the carboniferous period of palaeozoic era “Reptiles” arose from Labyrinthodont Amphibians. In the Mesozoic era “Reptiles” dominated the entire world and that era is called ‘GOLDEN AGE OF REPTILES”.

Cotylosauria’ is considered as “stem - reptiles”. They closely resemble the Labyrinthodont amphibians. It is not easy to distinguish these two groups separately.

In the Mesozoic era giant dinosaurs dominated the earth. In the late cretaceous period of Mesozoic era they became extinct

In the present day world nearly 5,000 known species of reptiles are living. Reptiles are poikiothennic vertebrates. They are first true land vertebrate’s. They are the first amniotic group of vertebrate animals.

The Present day reptiles are sphenodon, lizards, snakes, turtles and crocodiles.

GENERAL CHARACTERS OF REPTILES

 

The Reptiles origin from labyrinthodont Amphibians in the carboniferous period of Paleozoic era. Present day living Reptiles are 5,000 species. They have an endoskeleton of dry epidermal scales and in some, bony dermal plates are present.

The Reptiles flourished in the Mesozoic era. Gant Dinosaurs dominated the earth and seas. Mesozoic era is the “Golden age of Reptiies”. Most of the giant Reptiles became extinct in late cretaceous period of Mesozoic era era.

REPTILES-GENERAL CHARACTER

1) Reptiles are cold blooded Vertebrates.

2) Reptiles are terrestrial (or) aquatic animals.

3) The body of Reptiles is covered with horny scales (or) bonyscutes.

4)In Reptiles Skin is dry.

5) Glands are absent in the skin of Reptiles.

6) Four limbs are present. They are pentadactyl (having 5 fingers).

7) Skull occipital incompletely.

8) In Reptiles Vertebrae are gastrocentrous.

9) In Reptiles Ribs from a true sternum.

10) Respiration is carried on by the lungs.

11) In Reptiles Heart is divided into two auricles and ventricle is divided into2 chambers incompletely.

12) Right & left aortic arches are completely formed.

13) Red blood corpuscles are nucleated in Reptiles.

14) In Reptiles Kidneys are meta nephric. Each kidney is provided with separate ureter.

15) In Reptiles Twelve pairs of cranial nerves are seen.

16) Cloaca is present.

17) Fertilization is internal. Eggs are laid on land.

18) In Reptiles Extra embryonic membranes are present during the development of the embryo .

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