Zoology

Dissection of Rat With Labeled Diagram – Rat Dissection Labeled

Some glands make chemicals that are made of organic molecules. Since these glands don't have ducts like exocrine glands, they are called...

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Sourav Bio
This article writter by Sourav Bio on August 27, 2022

Writer and Founder of Microbiologynote.com. I am from India and my main purpose is to provide you a strong understanding of Microbiology.

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Dissection of Rat With Labeled Diagram - Rat Dissection Labeled
Dissection of Rat With Labeled Diagram - Rat Dissection Labeled

Contents

  • The rat is like any other animal. In the past, most undergraduate and postgraduate colleges in Indian universities used guinea pigs (Cavia sp.) for dissections. Rats are replacing guinea pigs because of how expensive they are right now.
  • There are four kinds of rats in India. Three of them live in the wild. The big ones are called Rattus rattus. R. rattus and R. bengalensis are often found in the godowns of homes in cities and towns.
  • Rattus norvegicus are medium-sized rodents that live in fields, farms, and rural homes, barns, and sheds.
  • Rattus norvegicus Albinus, or white rats, are still not a wild type. They are mostly raised and bred to be used in labs or as pets.
  • When it comes to routine dissection, guinea pigs have organ systems that are almost the same as those of rats. Wherever there are differences in structures, they are pointed out in the right places.
Rat Dissection Labeled
Rat Dissection Labeled

Killing of Rats

  • The poison chloroform is used to kill rats.
  • Rats in homes often have parasites on their bodies and on their fur.
  • Before the animals are used, they should be cleaned with phenol, Lysol, or another disinfectant and washed well with water.

Dissection of Rats

  • Place the specimen on its back on a tray for dissection.
  • Fix it by inserting pins through the limbs.
  • Lift the abdominal skin with forceps and create a small incision in the centre of the abdomen.
  • Beginning at the cut, make an incision extending anteriorly to the nose and posteriorly to the genital entrance.
  • Make transverse cuts along the limbs’ length.
  • Separate the skin from the muscles beneath it and pin it down.
  • Provide a transverse incision along the posterior abdominal wall.
  • Proceed laterally and anteriorly on both sides, severing the ribs to the anterior tho­racic cavity boundary.
  • Cut the clavicles and the surrounding muscles.
  • Raise the sternum and cut the diaphragm’s connection to the abdominal wall.
  • The ventral wall of the thorax and abdomen is split from the sternum, exposing the organs in the thoracic and abdominal chambers.
  • The neck’s underlying structures have been exposed by the removal of the skin.
Rat Dissection Labeled
Rat Dissection Labeled

General Viscera

Coelom

  • A vast cavity in the thoracic and abdominal regions that is delimited by the ventral abdominal wall, the lateral body walls, and the dorsal body wall.

Diaphragm

  • The coelom is divided into the smaller thoracic cavity in front and the larger abdominal cavity in back by a muscular barrier.
  • Organs contained within the coelome are referred to as viscera.
  • These organs reside in the thoracic cavity, which is split into three chambers by membranous tissue:
    • Pleural cavities: Two pleural cavities accommodate a lung each.
    • Mediastinum: The pericardial cavity, the oesophagus, and the blood vessels are all housed in the mediastinum, the space between the two pleural cavities.
    • Pericardial cavity: The heart, covered by two layers of pericardium, resides in a tiny chamber called the pericardial cavity.
    • Lungs: The lungs are a pair of sacs on either side of the heart that are spongy and a vivid pink. Although both lungs have lobes, the right lung has four and the left lung has none.
    • Oesophagus: The oesophagus is the tube that connects the pharynx and the stomach. It is a short, straight tube that is dorsal to the heart and medial to the lungs.

Organs are lodged in the abdominal cavity

The contents of the abdominal cavity include the following organs:

  • Liver: The liver is a big, ruddy-brown gland that is divided into four lobes—the right, the left, a median cystic lobe, and a posterior caudate lobe. Falciform ligament connects its posterior aspect to the diaphragm’s.
  • Stomach: The stomach is a big, curved pouch located on the left side, posterolateral to the liver.
  • Small intestine: The duodenum and ileum make up the small intestine, a long, skinny tube whose initial segment forms a loop.
  • Pancreas: The pancreas is a tiny, dispersed gland that sits on the duodenal mesentery.
  • Caecum: The caecum is a sizable blind appendage that forms at the base of the stomach and the beginning of the large intestine.
  • Large intestine: The large intestine is a tube that’s quite long. Colon is first and rectum follows.
  • Spleen: The spleen is a dark crimson organ located in the stomach’s greater curvature.
  • Kidneys: The kidneys are a paired organ that have bean-shaped, dark crimson bodies. The right kidney is in front of the left by a small margin. The ureter is an anatomical tube that extends from the internal hilus.
  • Adrenal glands: The adrenal glands are a pair of spherical organs located slightly above and in front of the kidneys.
  • Urinary bladder: The urinal bladder is a pear-shaped, muscular sac with a narrow neck that stores urine.
  • Ovaries: Female reproductive organs that are positioned ventrolateral to the kidneys and are small, compact, and yellow in colour.

A. Dissection of Alimentary System

  • When the skin on the back of the neck is taken off, the front part of the digestive tract is partially exposed.
  • The rest of the canal and its glands are in the thoracic and abdominal cavities.
  • Take out the heart, the sac around it, and the lungs.
Rat Dissection Labeled
Rat Dissection Labeled

1. Mouth

  • It is a pretty big opening at the front of the snout, and it is surrounded by two lips and jaws.
  • There are two different kinds of teeth.
  • The muscle on the bottom of the mouth, which is the tongue, fits into the groove on the palate.

2. Pharynx

  • A small space between the mouth and the back of the throat. (It affects both the digestive system and the respiratory system.)

3. Oesophagus

  • A thin, straight tube goes from the back of the throat through the diaphragm and into the abdominal cavity, where it connects to the stomach.
  • From the front, it is behind the larynx. In the neck, it runs in the same direction as the trachea.
  • It is behind the heart and lungs in the chest cavity.

4. Stomach

  • It is near the back of the diaphragm on the left side of the abdominal cavity.
  • The heart stomach is on the left side, has thin walls, and is clear.
  • The pyloric stomach is strong and clear, and it is on the right side of the body.

5. Small intestine

  • A tube that is the same size all the way along. It has two parts, called the duodenum and the ileum.

a. Duodenum

  • The first part of the small intestine is shaped like the letter U.

b. Ileum

  • It is a long tube with many turns that ends in the large intestine.

6. Caecum

  • A big, blind growth at the point where the small and large intestines meet.

7. Large intestine

  • It is made up of the colon and the rectum.

a. Colon

  • The large intestine’s first section. It’s not very long.

b. Rectum

  • Part of the large intestine that comes last. It is longer, and the opening is in the anus.

8. Liver (see general viscera)

  • The lobes’ bile ducts come together to make the common bile duct, which opens in the duodenum.

9. Pancreas

  • A type of gland with many small lobules that are spread out on the mesentery in the duodenal loop.
  • The lobules have tubes that connect to a common tube, which connects to the common bile tube and opens in the duodenum.

B. Dissection of Circulatory System

  • The heart, the veins, the arteries, and the capillaries are all parts of the circulatory system.
  • The heart is part of both the arterial system and the vein system.
  • Follow the steps above to expose the organs and the area around the neck.

1. The Heart

  • It’s stuck in the pericardial cavity on the left side, near the front of the thoracic cavity, and it’s tilted a little bit.
  • Take off the fat and the two-layered pericardium that covers the heart.
  • It is round, reddish brown, strong, and has four chambers.
Rat Dissection Labeled

2. Atria (auricles)

  • Two muscle chambers that are smaller than the ventricles and sit in front of them.
  • On the ventral side, between the two atria is a large pulmonary artery.
  • The three systemic veins, which are made up of two precavals and one postcaval, all go straight into the right atrium.
  • The two pulmonary veins both come out of the left atrium through the same hole.
Rat Dissection Labeled
Rat Dissection Labeled
Rat Dissection Labeled
Rat Dissection Labeled

3. Ventricles

  • Together, the two ventricles make up the main part of the heart, which is a muscle structure with thick walls.
  • The two ventricles are separated by an oblique groove.
  • The size of the left ventricle is bigger than that of the right.
  • The right ventricle is where the pulmonary artery starts, and the left ventricle is where the aortic arch starts.
  • There is no right aortic arch.

C. Dissection of Venous System

  • Turn the ventricle up and find where the two systemic veins, the right and left precavals (cranial vena cava) and the post caval vein (caudal vena cava), the third systemic vein, and the common pulmonary vein enter the right atrium and the left atrium, respectively.
  • Find the two antecedents. The veins they are getting are different from each other.
  • Show the blood vessels that make up the post-caval vein and the hepatic portal system.
  • There is no portal system in the kidneys.

1. Precaval veins

  • Blood from the front of the body flows back through the precaval veins.
  • The one on the right is short, while the one on the left is quite long.
  • Several veins come together to make a precaval vein.
  • The veins that make up the right and left precavals are the same, except that the right has the superior intercostal vein and the left has the azygos vein.
  • The external jugular is made when the muscles of the head, jaws, tongue, and salivary glands connect the front and back facial veins.
  • As it goes back, it gets:
    • Back and neck muscles make up the posterior external jugular.
    • From the shoulder to the head.
    • Blood flows out of the sternum through the internal jugular.
    • A short vein is subclavian.
  • It gets:
    • the internal mammary duct from the sternal duct.
    • The axillary is made when the brachial, subscapular, and axillary veins come together.
    • Brachial comes from the arm.
    • Subscapular is from the area around the shoulder.
    • The precaval vein is made when the external and internal jugular veins and the subclavian vein come together.

Right precaval

  • It also gets the superior intercostal vein from the upper part of the thoracic wall, which is not listed above.

Left precaval

  • In addition to the veins listed above, it gets an azygos from the lower part of the thoracic wall. This is formed when the intercostal and subcostal veins join. 

2. Postcaval vein

  • It is a large vessel in the middle of the body that is made up of several veins that bring blood from organs in the back and middle of the body.
  • The caudal takes blood from the tail and connects to the postcaval where it starts to form.
  • Internal iliac from the area around the bladder and pelvis.
  • External iliac formed by the union of:
    • Femoral from the hind limb.
    • Epigastric from abdominal muscles and urinogenital system.
  • The two iliacs come together to make one big iliac. The postcaval vein is made up of the two common iliacs that come together. At the point where the caudal and postcaval meet, they connect.

Lumbar and iliolumbar

  • A few sets from the lower back.

Genital

  • Linked, they come from the testes or ovaries and the parts that go with them.
  • The right one goes to the precaval vein, while the left one goes to the renal vein.
  • Since the testes are in the scrotum, these veins are long in men.
  • They are short on women.

Renal

  • The kidneys send out a pair. The right kidney is a little farther forward than it should be.

Hepatic

  • They come from the liver’s lobes in pairs.
  • The postcaval vein goes through the diaphragm, and when it gets to the thoracic cavity, it gets blood from

Phrenic

  • From the diaphragm, paired.

Hepatic Portal System

  • It is made up of veins that go into the liver. It starts near the pylorus and goes all the way to the liver.
  • The inferior mesenteric artery comes from the rectum.
  • The superior (front) mesenteric nerve comes from the ileum, caecum, and colon.
  • Duodenal from duodenum.
  • Lienogastric comes from the words liver, spleen, and pancreas.
  • The veins come together to make the hepatic portal vein, which has branches that end in the liver.

3. Pulmonary veins

  • Veins that are small but wide and don’t connect to bigger veins.
  • From the right lung, blood is brought back by a single vein, and from the left lung, blood is brought back by two veins that join together to make one vein.
  • The two veins come together to make a single pulmonary vein that starts in the left atrium.

D. The Arterial System

The Arterial System
The Arterial System

1. The aortic arch (Systemic aorta):

  • At the bottom of the left ventricle is where the aortic arch starts.
  • It starts on the left side of the thorax, curves around the left bronchus, and runs along the mid-dorsal line of the thorax and abdomen as the dorsal aorta.
  • Follow the paths of the branches that the aorta sends off.

a. Innominate

Starts on the right side of the arch and splits into two parts:

i. Right common carotid runs to the head lying parallel to the trachea.

It splits into two again: 

  • The internal carotid goes to the side of the head and enters the skull.
  • External carotid artery, middle, gives blood to the head, jaw, and tongue.

ii. Right subclavian runs outward between the first rib and clavicle.

It sends out the following:

  • The vertebral column moves forward and enters the cranium.
  • Cervical runs next to the external jugular vein and gives blood to the muscles in the neck.
  • The sternal region is fed by the internal mammary.
  • Costocervical gives blood to the neck and the upper part of the chest wall.
  • Subscapular connects the upper arm, shoulder blade, and chest.
  • The brachial goes on in the forearm.
  • On the left side, there is no innominate artery.

The common carotid on the left side comes straight from the aortic arch. The branches of the right common carotid are similar.

The left subclavian comes out of the aortic arch straight. The branches are the same as the ones on the right side.

b. Dorsal aorta

Runs from the back to the middle, sending branches to the next organs.

  • Intercostals: A few pairs of small arteries that bring blood to the walls of the thorax.
  • Phrenic: A pair of small arteries that bring blood to the diaphragm.
  • The dorsal aorta goes through the diaphragm and goes into the belly. It goes away
    • Coeliac: Branches go to the stomach, liver, and spleen, but they are not paired.
    • Anterior mesenteric: The pancreas, ileum, caecum, and colon are all fed by the pancreas mesentery, which is a single nerve that starts above the kidneys.
    • Renals: Renals, which come in pairs, feed the kidneys. The right kidney came from a different place than the left kidney.
    • Genitals: The left one comes from the left renal artery and the right one comes from the dorsal aorta. Give the gonads, testes or ovaries, and genital ducts what they need. In men, these arteries are long and run from the back of the abdomen to the front of the abdomen. They supply the testes and other structures in the scrotum.
    • Lumbar: A few pairs of nerves behind the kidneys send nerve impulses to the dorsal muscles of the lumbar area.
    • Iliolumbar: This nerve is not paired, is behind the lumbar, and sends branches to the iliac region and the dorsal abdominal wall.
    • Posterior mesenteric: Unpaired, starts near where the dorsal aorta splits, gives blood to the descending colon and rectum.
    • Typical iliacs: Right and left come from the same place. Each one splits into two main paths:
      • The external iliac nerve goes to the abdominal wall and becomes the femoral nerve in the back legs.
      • The internal iliac runs backward and gives blood to the pelvis.
    • Caudal: A narrow artery that runs the length of the tail. It is a branch of the dorsal aorta.

2. Pulmonary trunk

  • As soon as it leaves the right ventricle, it goes to the back and splits into two branches that go to the two lungs.

E. Dissection of Cranial Nerves

  • The skull is made of bones, and the bones are very strong.
  • The joints between the bones of the head stand out.
  • To see the brain and the roots of the cranial nerves, use a pointed arm bone cutter or, better yet, a small hand drill to make a hole where the frontals and parietals meet.
  • Remove the bones, being careful not to hurt the nerve roots in the head.
  • Rats have twelve sets of cranial nerves.
Rat Dissection Labeled
Rat Dissection Labeled

1. Fifth (V) cranial nerve

The first nerve in the medulla oblongata is the fifth, also called the trigeminal nerve. It comes out of a side part of the pons. As soon as it starts, it splits into three branches:

a. Ophthalmic

It splits into three paths that all lead forward:

  • Lachrymal goes to the tear gland between the eyes and the conjunctiva.
  • The frontal nerve goes through the orbit, comes out near the upper eyelid, where it sends branches, and then goes forward to supply the skin of the forehead.
  • The nasociliary enters the orbit, crosses to the middle wall, and goes through the anterior ethmoidal foramen. It is now called the anterior ethmoidal nerve. It goes into the cranial cavity, runs forward to the nasal cavity after going through the cribriform plate, and sends branches called internal nasals to the mucous membrane. Leaving the nasal cavity as it is, it gives nerves to the nose’s wings and tip.

b. Maxillary

Maxillary moves forward, enters the orbit, goes through the infraorbital groove and canal, and comes out through the infraorbital fissure. The nerve splits into nine branches that go to the sides of the nose, the upper and lower lips, and the inside of the cheeks.

c. Mandibular 

Mandibular goes down and forward, then splits into two branches. Nervus spinosus goes back into the skull and sends nerve signals to the dura mater.

  • The internal pterygoid splits in two, and the mandible comes from the anterior trunk.
  • The pinna of the ear, the temporomandibular joint, the skin of the temporal area, the mucous membrane of the mouth, the tongue, teeth, and the skin of the lower jaw are all controlled by the posterior trunk.

2. Seventh (VII) cranial nerve

The third nerve in the medulla oblongata is the facial nerve, which is the seventh nerve. It starts at the front edge of the medulla and goes into the facial canal. From there, it goes through the stylomastoid foramen and out of the body. It has four different parts:

  • The outer layer of petrosal goes along the side of the carotid artery and through the middle ear. It sends nerve impulses to the soft palate and lacrimal gland.
  • Palatine goes backwards and up between the outer ear and mastoid process to the auricle. It gives blood to the palate and nasal area.
  • Hyomandibular: The superficial branches go forward and backward over the zygomatic arch and the neck branches. The muscles in the lower jaw and lip are fed by a deep branch.
  • Chorda tympani goes into the tympanic cavity, crosses the tympanic membrane, and sends nerves to the snout, tongue, and salivary glands as it leaves the tympanic cavity.

3. Ninth (IX) cranial nerve

  • The fifth nerve in the medulla is the ninth, or glosopharyngeal nerve. It starts on the back of the auditory nerve on the posterolateral side of the medulla and runs between the external and internal carotid arteries. It’s in two parts:
  • The pharyngeal branch of the vagus is joined by a small branch called the pharyngeal branch. This helps form the pharyngeal plexus.
  • The main nerve, called the glossal nerve, runs forward and gives feeling to the tongue, pharynx, and floor of the mouth.

4. Tenth (X) cranial nerve

The vagus nerve comes from the part of the medulla that is near the back and front. It comes out through the posterior lacerated foramen and has a nodosum ganglion, from which two nerves come out.

a. The pharyngeal branch of the glossopharyngeal nerve connects to the front end of the ganglion.

b. The posterior end of the anterior laryngeal nerve goes to the larynx and thymus gland.

The vagus nerve goes backward through the neck and thorax before going into the abdomen. It has two branches coming off of its neck.

c. Laryngitis that comes back:

It goes through the aortic arch on the left side and makes a loop around the start of the subclavian artery on the right side. The nerves go forward along the line between the oesophagus and the trachea. They send branches to both of these organs and supply the larynx and diaphragm with nerves.

d. Cardiac gives the heart and major blood vessels nerves.

e. Pulmonary gives oxygen to the side lung.

f. Gastric: The main stem goes backward, sends small branches to the oesophagus, and pierces the diaphragm at the same time. It sends branches to the liver from the abdomen. The right vagus ends on the back of the stomach, and the left one ends on the smaller curve and front of the stomach.

F. Dissection of Brain

  • Use the same method you used for Channa punctatus to get the brain out.
  • Put it in water in a petri dish with a high rim.
  • Some parts of the dorsal surface of the brain can’t be seen because the cerebrum and cerebellum are so big and the cerebellum goes through so many structural changes.
Dissection of Brain
Dissection of Brain

1. Dorsal View of the Brain

a. Olfactory bulbs

  • Small, club-shaped growths on the front of the brain that come in pairs.
  • They are connected to the two sides of the brain. Each olfactory bulb has an olfactory nerve coming out of it.

b. Cerebral hemispheres

  • Two large bodies that are long and thin with wide bases and are joined in the middle.
  • Together, they make up the brain.
  • The lateral temporal lobe, the anterior frontal lobe, the median parietal lobe, and the posterior occipital lobe are all parts of the cerebral hemisphere.
  • The thalamencephalon and the optic lobes are covered by the hemispheres of the brain.

c. Corpus callosum

  • A structure that runs across the brain and connects the two hemispheres.

d. Pineal body

  • A small, round mass at the back of the brain where the two halves meet.

e. Mesencephalon (mid brain)

  • Almost none of it can be seen.

f. Cerebellum

  • It is very big and has a central lobe and two side lobes that are separated by many cracks.
  • Each side lobe has a bump called the flocculus that has an odd shape.

g. Medulla oblongata

  • It is bigger in the front and gets smaller as it moves back, becoming the spinal cord.

2. Ventral View of the Brain

a. Hippocampal lobe

  • From the base of each hemisphere of the brain, there is a narrow, ridge-like structure that goes forward.

b. Corpora striata

  • A band of white fibres that runs across the back of both hemispheres of the brain.

c. Optic chiasma

  • It has nothing to do with the brain. The optic chiasma is made when the nerves that come from the optic lobes cross in front of the infundibulum.

d. Infundibulum

  • A process that goes from the floor of the diencephalon to the middle of the head.

e. Pituitary body (Hypophysis)

  • Attached to the infundibulum is a body with a round shape.

f. Crura cerebri

  • These are prominent bumps on the midbrain’s floor.

g. Pons varoli

  • A flat band of fibres that run from one side of the cerebellum to the other.

G. Dissection of Neck Region

Follow the carotid artery carefully and pay attention to the nerves that are next to it. Expose the nerves that run along the outside of the pneumogastric.

  • Vagus nerve: The vagus, also called the pneumogastric nerve, is a thick nerve that starts with a ganglionic swelling. From the foramen lacerum posterius, it goes down and back along with the carotid artery in the neck.
  • Anterior laryngeal nerve: The anterior laryngeal nerve is a thin, delicate nerve that comes from the pneumogastric nerve at the top edge of the thyroid cartilages. It gives the mucous lining of the larynx nerves.
  • Depressor nerve: This nerve comes from the anterior laryngeal nerve and is thin. It goes back along the back of the neck to the carotid artery and gives the heart its nerves.
  • Posterior laryngeal or recurrent laryngeal: Posterior laryngeal, also called recurrent laryngeal, is a nerve that comes from the vagus nerve or pneumogastric nerve just above the heart and runs along the side of the trachea.
  • Cervical sympathetic nerve: The cervical sympathetic nerve is a thin nerve that runs from the vagus nerve to the depressor nerve. It grows into the anterior cervical ganglion and the middle cervical ganglion and the posterior cervical ganglia in the front and back, respectively.
  • Phrenic nerve: The phrenic nerve comes from the fourth cervical nerve and runs along the back of the spine. The phrenic nerve splits into several small nerves in the diaphragm after it goes through the thorax.

H. Dissection of Urinogenital System

  • Rats don’t have two separate systems for their urine and genitalia.
  • They are called the urinogenital system as a whole.
  • In this species, the only part of the two systems that work together is the male’s urethra, which is used by both urine and sperms.
  • The system is in the back of the abdominal cavity. Follow the same steps that were used for Calotes sp. to see the urogenital organs.
  • Take off the fat that is covering the testicles that are stuck in the scrotum.
Rat Dissection Labeled
Rat Dissection Labeled
Rat Dissection Labeled
Rat Dissection Labeled

The Urinary (Excretory) System

Kidneys

  • Two dark red bodies in the shape of a bean with a notch on the inside. This is called the hilus.
  • The right kidney is in front of the left one by a small amount.

Ureters

  • From the hilus come the tubes that drain urine. They are long, thin, tube-shaped, and lie against the back wall of the abdomen. They go backward and open separately on the dorsal side of the narrow neck of the urinary bladder.

Urinary bladder

  • A small, muscular sac that looks like a pear and has a narrow neck that opens into the urethra.

Urethra

  • A tube that goes on from the bladder’s neck.
  • In men, the urethra is long and strong. It goes through the penis and opens at the tip of the penis.
  • In females, it has a hole that leads to the outside that is right behind the clitoris.

I. Dissection of Genital System

1. Male Urogenital System Of Rat​

For the urinogenital system, cut the sides of the pubic symphysis and take out the piece that was cut so that the back part of the urinogenital system can be seen. This system includes the organs that deal with urine and sperm.

a. Urinary organs or kidneys

You already know where the kidneys, which are surrounded by fat, are. The place where the kidney meets the ureter is called the hilus. Also look at the ureter and follow it up to the bladder.

Take out one kidney and look at the hilus. This is where the ureter and blood vessels go in and out of the body. With a sharp scalpel, cut the kidney open down the middle and take note of the following parts:

b. Genital organs

Note the following parts :

  • Testes: A pair of testes is found in the scrotal sacs (right and left). The scrotal sacs are a pair of pouches in front of the anus and between the hind legs. The testes can be exposed by cutting the scrotal sacs. Each testis is elongated and ovoid body attached to the hinder end of the scrotal sacs by band of tissues called gubernaculum. In the very infant rat the testes lie in the abdomen close to the kidneys and just before maturity, they descend into the scrotal sacs along the inguinal canals.
  • Epididymis: It is an irregular and in the middle corpus epididymis convoluted tube, found along the inner edge of testis. At anterior end it forms caput epididymis and at posterior end cauda epididymis. Cauda epididymis gives rise to vas deferens.
  • Vas deferens: Each vas deferens coils round the ureter from the outside before opening into the urethra behind the urinary bladder.
  • Urethra: It is the common duct for urine and sperms opening into the penis.
  • Penis: It is the copulatory organ through which sperms are discharged into the female genital organ, i.e., vagina of the female. The urethra opens at the tip of the penis by a slit-like opening. The tip of the penis is covered by loose skin called prepuce.
  • Spermatic cord: It is an elongated cord-like structure made up by connective tissue, blood vessels and nerves, which originate from the caput epididymis and running to the body cavity through the inguinal canal.                                                                                                 
  • Accessory glands: The following glands are associated with male genital system :
    • Ampullar glands: The outer end of the vas deferens near the entrance into the urethra is enlarged into the ampulla, which contains ampullar glands to secrete mucus.
    • Vesicular glands: They are branched glands originating from the vas deferens behind the ampulla.
    • Prostate gland: It is a large and lobulated gland, situated just behind the junction of urinary bladder with the vasa deferentia.
    • Preputial glands: They originate from the inner fold of skin forming prepuce. They secrete odorous secretion.
    • Cowper’s glands: They originate from the urethra at the base of the penis. They produce mucous secretion during sexual excitement and also protect the sperms from traces of acids found in urethra.
  • Seminal vesicle: A pair of seminal vesicles which open into urethra by a common duct other structures seen are right and left kidneys, adrenal gland, right water, left ureter, pelvis, rectum and anus.  

Pay attention to the following:

  • Testes: The scrotal sacs hold a pair of testes (right and left). There are two pouches in front of the anus and between the back legs. These are the scrotal sacs. By cutting the scrotal sacs, the testes can be seen. Each testicle has a long, rounded body called the gubernaculum that connects it to the back end of the scrotal sacs. The testes of a very young rat are in the abdomen near the kidneys. Just before the rat grows up, they move down the inguinal canals and into the scrotal sacs.
  • Epididymis: This is an irregular, twisted tube that runs along the inside of the testis. It is in the middle of the corpus. At its front end, it becomes the caput epididymis, and at its back end, it becomes the cauda epididymis. Cauda epididymis gives rise to vas deferens.
  • Vas deferens: Each vas deferens wraps around the ureter from the outside and opens into the urethra behind the urinary bladder.
  • Urethra: The urethra is the tube that leads urine and sperm to the penis.
  • Penis: It is the part of the body where sperm are released into the female genital organ, which is the vagina. The urethra opens in a slit-like way at the tip of the penis. The loose skin at the tip of the penis is called the prepuce.
  • Spermatic cord: The spermatic cord is a long cord-like structure made of connective tissue, blood vessels, and nerves. It starts at the tip of the epididymis and goes through the inguinal canal to the body cavity.
  • Accessory glands: The male genital system is made up of the following glands:
    • Ampullar glands: The end of the vas deferens closest to where it enters the urethra is enlarged into the ampulla. The ampulla has mucus-making glands called ampullar glands.
    • Vesicular glands: Vesicular glands are glands with branches that come from the vas deferens behind the ampulla.
    • Prostate gland: The prostate gland is a large, lobulated gland that is right behind where the urinary bladder and vasa deferentia meet.
    • Preputial glands: Preputial glands start in the inner fold of skin that makes up the prepuce. They make smelly secretions.
    • Cowper’s glands: Cowper’s glands are at the base of the penis. They come from the urethra. During sexual excitement, they make mucus and protect the sperm from small amounts of acid in the urethra.
  • Seminal vesicle: Two seminal vesicles that open into the urethra through a common duct. The right and left kidneys, adrenal gland, right water, left ureter, pelvis, rectum, and anus can also be seen.
Rat Dissection Labeled
Rat Dissection Labeled

Hormones

Some glands make chemicals that are made of organic molecules. Since these glands don’t have ducts like exocrine glands, they are called ductless glands or endocrine glands, and the chemicals they make are called hormones.

Dissection

  • Follow the same steps used for rats to expose the thoracic and abdominal cavities.

1. Thyroid gland

  • Behind the thyroid cartilage and the larynx, at the front end of the trachea. Take out the fat, lymph nodes, and salt glands. If you cut along the mid-ventral line of the sternohyoid muscles, you can see the thyroid gland.
  • The largest endocrine gland is the thyroid. It is in a capsule that has two layers. From the inner capsule, the septa of the fibroelastic capsule grow inward and divide the gland into tubules.

2. Parathyroid gland

  • Two sets. Small, yellow glands that are very close to the thyroid. One set is on each side of the thyroid.

3. Thymus gland

  • A large, pink gland in the thorax that surrounds the base of the aorta. When it’s young, it’s pretty big, but as it gets older, it gets smaller and smaller.

4. Adrenal (Suprarenal) gland

  • There are two glands, and each one is attached to the front of a kidney by fatty tissue. A thick capsule of fibrous connective tissue surrounds the gland.

5. Islet of Langerhans

  • The islets are tucked away in the tissue of the pancreas, and they can only be seen in histological sections of the pancreas.

6. Pituitary gland

  • It is an oval body that is attached to the back of the brain, just behind where the optic nerves cross.
  • The infundibulum connects it to the brain, and the duramater covers it.
  • The gland has three lobes: the anterior, middle, and back lobes.

7. Gonads

  • The testes and ovaries work together to make hormones. The testicles are in the scrotum of a male.
  • In females, the ovaries are on the side of the kidneys that faces the back.

References

  • http://cshprotocols.cshlp.org/content/2008/4/pdb.prot4803.abstract
  • https://www.brainkart.com/article/Dissection-of-a-Rat_21350/
  • https://www.biologycorner.com/worksheets/rat_dissection.html
  • https://assist.asta.edu.au/sites/assist.asta.edu.au/files/SOP%20Performing%20a%20rat%20dissection-FINAL_DB%20(3).pdf
  • https://www.biologydiscussion.com/zoology/dissection/dissection-of-rat-with-diagram-zoology/
  • https://www.faunafondness.com/rat-dissection/
  • http://www.jonesbiology.com/biology-2—human-biology/rat-dissection
  • https://www.faunafondness.com/rat-dissection/
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