Dissection Of The Rabbit
Dissection of the Rabbit
Dissection of the RabbitContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Unit 1: External Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Unit 2: The Skeletal System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Unit 3: The Muscular System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Unit 4: The Digestive System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Unit 5: The Respiratory System. . . . . . . . . . . . . . . . . . . . . . . . . . . 15Unit 6: The Circulatory System . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Unit 7: The Urogenital System . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Unit 8: The Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Rabbit illustration on pg. 1 DILEEP/Shutterstock.com 2012 Carolina Biological Supply Company Printed in USA.
IntroductionAs you progress through this investigation ofrabbit anatomy, consider how the form of eachparticular structure is appropriate for itsfunction. For example, the rabbit’s sharpincisors enable it to cut the herbaceous plantsthat it eats and to gnaw through roots whenburrowing. Correlating form with function is apart of any in-depth anatomical study. Beforeyou begin the dissection, read the entireprocedure carefully and familiarize yourselfwith the following list of commonly used terms.Important terms are boldfaced if they appear ina corresponding figure.Until the early 20th century, rabbits wereclassified as rodents; however, they differ fromrodents in several ways and are now classed inthe order Lagomorpha, with hares and pikas.The majority of domestic rabbits, includingyour dissection specimen, are derived from theEuropean rabbit, Oryctolagus cuniculus. In thewild, this species lives in groups that formelaborate systems of burrows referred to aswarrens. Domestic rabbits have been eitheraccidentally or purposely introduced to manyhabitats in which they then over-proliferated,disrupting the native ecosystem.Midsagittal ximalDistalLateralMedialTransverseplaneFigure 1. Body planes and directions.1
SafetyWear safety glasses or goggles, gloves, and alab apron when dissecting the specimen.Perform the dissection only on the dissectiontray. Follow proper hygiene practices before,during, and after the lab.Direction or PlaneDefinitionLateralToward the right or left sideMedialToward the midlineProximalNear or toward the point of referenceDistalAway from the point of referenceDorsalToward the backVentralToward the bellyAnterior (cranial)Toward the headPosterior (caudal)Toward the tailSuperficialToward or along the surfaceDeepA significant distance below the surface2
Unit 1External AnatomyLay your specimen on its ventral surface.Examine its exterior carefully. Note that therabbit can be divided into three sections, thehead, trunk, and tail. The head is separated fromthe trunk by the neck.Note the hair. The presence of hair, at least atsome point in their development, is adistinguishing feature of mammals. Hair serves avital role in thermoregulation in most species ofmammals and also protects the skin. Specializedhairs, vibrissae, or whiskers, are typically foundon the face. They are used as part of the rabbit’ssensory system and help the animal gatherinformation about its surroundings. Examine thehead to view the vibrissae.While examining the head, note the othersensory structures. The rabbit’s eyes are largeand set laterally on the head. Lateral positioningincreases field of vision but reduces depthperception. Also due to the placement of theeyes, a rabbit has a small blind spot directly infront of its face. This eye positioning is commonTailTrunkHeadFigure 2. The three sections of the rabbit3
much as 10 percent of the overall surface areaof a rabbit.Open the mouth of the rabbit and examine itsdentition. Like a rodent, a rabbit has incisorsthat are open-rooted and grow continuouslythroughout the animal’s life. Unlike a rodent,a rabbit has four incisors in its upper jaw. Thesmaller pair behind the front incisors are referredto as peg teeth. As you examine the dentition,consider the rabbit’s diet. Observe the sensoryorgans located in the mouth, the taste buds.Rabbits have a good sense of taste. Like humans,rabbits can taste the four basic categories offlavors: sweet, sour, bitter, and salt. It is not yetknown if they are able to taste the umami flavor.The sense of taste helps a rabbit determinepotential toxicity and nutritional value of theplants that it nibbles.It is in the mouth that the digestion of foodbegins. Food is mechanically broken down bythe teeth, while salivary enzymes begin thefood’s chemical breakdown.After examining the rabbit’s head, examine itstrunk. Note the paired feet and legs of the rabbit.The feet and legs of the rabbit are modified forhopping, also known as saltatorial locomotion.Mammals with saltatorial locomotion tend tohave enlarged muscular hind limbs and reducedforelimbs and to live in open spaces.in animals that have many predators. Comparedwith humans, rabbits tend to be farsighted—theirfocus is worse on things that are nearby butbetter on things at a distance (such asapproaching predators). Rabbits tend to becrepuscular (most active near twilight and dawn)and have good vision in low light conditions.Protecting the eyes are upper and lower lids anda partial nictitating membrane located in themedial corner of the eye. Because it istransparent, the nictitating membrane allows forsome protection and moistening without as greatof a loss of vision as blinking of the eyelids. Inmany animals, including some mammals, acomplete nictitating membrane can cover theentire front of the eye. Humans retain only avestige of the nictitating membrane.The nares, or nostrils, are not only theopenings to the respiratory system but are alsocrucial to the sensory system, allowing rabbitsto gather olfactory information from theirenvironment. The nares are enclosed by lateralfolds which radiate from the median cleft.The external part of the ear, the pinna (pl.,pinnae), directs sound waves into the auditorymeatus, or ear canal. A rabbit can hear agreater range of frequencies than a human. Thepinnae function also in thermoregulation; infact, the surface area of the ears may occupy cisorsFigure 3. The external anatomy of the rabbit’s head4
Unit 2The Skeletal SystemThe skeletal system of the rabbit is comprisedof both cartilage and bone. The system servesto support the body mass and to protect internalorgans. The skeletal system consists of twomain parts, the axial skeleton and theappendicular skeleton. The axial skeleton is theskull, vertebral column, ribs, and sternum. Theappendicular skeleton includes the pectoral and8 910pelvic girdles and their appendages. Thepectoral appendages are the forelimbs, and thepelvic appendages are the hind limbs. Duringyour dissection of the rabbit, refer to theskeleton diagram to identify the bones thatyou encounter. Observe the structure andarrangement of the bones as you consider theirspecific functions.1176155171612131443 NasalPremaxillaMaxillaFrontalOptic .20.21.22.23.24.25.26.3938Cervical vertebra (7)Thoracic vertebra (12)Ribs (12)Lumbar vertebra (7)Sacral vertebra (4)Caudal vertebra (16)ScapulaClavicleHumerusSternumXiphoid processOlecranon processRadiusFigure 4. The skeletal structure of the rFibulaTibiaPatellaTarsalsMetatarsals
Unit 3The Muscular SystemThe muscular system consists of skeletalmuscle, which contracts to move bones. Atypical skeletal muscle is attached to two bonesby tendons. The attachment point to the bonethat is moved during contraction is called themuscle’s insertion. The muscle’s origin is thestationary point of attachment. To observe themusculature, you must first skin the rabbit asdescribed below. After removing the skin, referto the muscle diagrams to identify the superficialmuscles of the rabbit. Consider the function ofeach muscle as you examine it. Try to find theorigin and insertion of some of the muscles thatyou examine.skin away from the body and then cut throughthis muscle’s attachment points to the trunkalong the midline and in the axillary (armpit)region of the rabbit. Be careful not to damageany of the other muscles. Finally, remove theskin by pulling it down from the ventral cranialregion toward the caudal region. Skin shouldremain only on the feet, head, tail, and genitaliaof the rabbit.Skinning the rabbitLay the rabbit on its ventral surface. Massagethe skin in the dorsal neck area to loosen aportion of the skin from the underlying muscle.With a scalpel, make a small incision in the centerof the area of loosened skin. Using blunt-tippedscissors, cut a shallow incision down the dorsalmidline toward the tail. As you cut, pull the skinaway from the underlying muscles. From thiscut, make additional cuts down the lateral surfaceof each leg and around the wrists and ankles.Additionally cut around the neck, tail, anus, andexternal genitalia. Ensure that you do notdamage the genitalia while making the cuts. Afterall cuts are made, separate the skin from theunderlying muscles by using a blunt probe totear through the superficial fascia while pullingthe skin away from the body. As you separate theskin near the neck you will see the platysma, fineparallel muscle fibers that are attached to theskin. Remove this muscle as you remove theskin. As you separate the skin from the muscleson the rabbit’s ventral surface, you will see thatthe skin is attached to a thin sheet of muscle, thecutaneous maximus, which originates at thelinea alba (midline). To remove the skin, pull theFigure 5. Incision lines for skinning6
Dorsal Superficial Pectoral MusclesVentral Superficial Pectoral sLevator scapulae dExtensor carpi radialis longusExtensor brevis pollicisRadiusTransverse ligamentUlnaExtensor carpi ulnaris12.13.14.15.16.17.18.19.20.21.Extensor communis digitoriumExtensor digiti propriusFlexor carpi ulnarisOlecranon processTriceps brachii, lateral headAcromiotrapeziusLatissimus dorsiSpinotrapeziusExternal obliqueSternohyoidFigure 6. Superficial pectoral dJugular veinBasioclavicularisCleidomastoidPectoralis tenuisCleidohumeralisPectoralis majorCutaneous maximusLatissimus dorsiExternal oblique
Dorsal Superficial Pelvic MusclesVentral Superficial Pelvic 5.6.7.8.9.10.11.Dorsal aponeurosisGluteus mediusGluteus maximusRectus femorisTensor fascia lataBiceps femoris anteriorVastus intermediusVastus lateralisBiceps femoris posteriorExtensor digitorum longusGastrocnemius anosisAdductor magnusGracilisExternal obliqueRectus femorisVastus medialisSartoriusAbductor caudaeSemimembranosisGracilisAdductor magnusFigure 7. Superficial pelvic muscles8
Unit 4The Digestive SystemSecure the skinned rabbit on its dorsal side inthe dissection tray. Following the incision linesdepicted in the diagram, cut through themuscular wall of the abdomen from the pubicarch to the most posterior rib. Cut two additionalincisions from the linea alba to the dorsal side ofthe rabbit, almost to the vertebral column.Carefully fold the flaps of skin and musclelaterally. Do not disturb the underlying organs.Pin the flaps to the tray to expose the abdominalcavity. There are two body cavities separated bya thin sheet of muscle called the diaphragm. Theexposed cavity is the abdominal cavity. Anteriorto that cavity and separated by the diaphragm isthe thoracic cavity.A prominent organ in the anterior of theabdominal cavity is the liver. This reddishbrown organ is divided into right and left lobesby the falciform ligament. Each of these lobes isfurther divided into median and lateral lobes,for a total of four lobes of the liver. The liverproduces some amino acids, filters the blood,converts harmful substances into harmlessones, and helps to regulate blood sugar.Additionally, in the digestive system, the liverproduces bile, which emulsifies fat duringdigestion. The bile produced by the liver isstored in the gallbladder. Raise the right lobe ofthe liver and observe the gallbladder, a dark,greenish-yellow sac.LiverLarge intestineDiaphragmSmall intestineFigure 8. Abdominal cavity9
LiverGallbladderLiverFigure 9. Abdominal cavity showing the gallbladderEsophagusAs you continue to examine the abdominalcavity, trace the path of food through thedigestive system. Each swallow of food forms abolus, which travels from the mouth down theesophagus. The majority of the esophagus,located in the thoracic cavity, is best examinedduring observation of the circulatory system.Some small portion may be visible at the mostanterior portion of the stomach. After leaving theesophagus, the food reaches the stomach,located on the left side of the rabbit, beneath thediaphragm. Lift the liver to view the entirestomach. The stomach consists of four portions:the cardia, the fundus, the body, and the pylorus.The cardiac portion is the area where thestomach joins the esophagus. In this section, thecardiac sphincter separates the esophagus fromthe stomach. (Malfunction of this sphincter is acause of acid reflux in humans.) The fundus isthe upper curve of the stomach that lies tothe left side of the esophagus. The body isthe main portion of the stomach. Thepyloric section lies to the right of theesophagus and terminates in the pyloricsphincter, which separates the stomach from theduodenum, the first portion of the smallCardiac regionFundusGreater cuLesrvaserturecurvatureCardiacsphincterPyloric regionPyloricsphincterFigure 10. Digestive system diagram10
LiverStomachFigure 11. Abdominal cavity showing the stomachStomachSpleenFigure 12. Abdominal cavity showing the spleen11
sections of the small intestine, which aredifficult to distinguish. The caudal end of theileum is modified into a round muscularenlargement called the sacculus rotundus. Thesacculus rotundus is a structure found only inrabbits. It has a large amount of lymphoid tissueand is involved in the immune system. Carefullycut longitudinally along a portion of the smallintestine and examine the lining with a handlens. The small intestine is lined with thousandsof circular folds, the plicae circulares. There arealso small projections called villi. Each villus hasits own projections, the microscopic, hair-likemicrovilli. The folds and projections increasethe surface area of the small intestine andmaximize the absorption of nutrients. The smallintestine ends at the ileocecal valve. Within themesentery of the small intestine is the pancreas,a pinkish-brown, somewhat granular mass. Thepancreas opens to the small intestine throughthe pancreatic duct at the caudal end of theduodenum. It is part of both the digestive andendocrine systems and secretes both enzymesand hormones.intestine. In the stomach, chemical andmechanical digestion continue as muscularcontractions mix the bolus with digestivesecretions, forming a mixture called chyme.Open the stomach and remove any food from theinner surface. Examine the internal surface of thestomach. Note the deep folds, or rugae, thatallow the stomach to expand without pressure.(A hands lens may help you see greater detail.)Though not part of the digestive system, thespleen is best viewed at this point. The spleen islocated on the greater curvature of the stomach,the larger convex curve. It is a small, dark,reddish-brown organ. The spleen is part of thelymphatic system and is designed to filter blood.From the stomach, the chyme travels throughthe pyloric sphincter into the duodenum, thefirst section of the small intestine. It is here thatthe common bile duct from the liver andgallbladder and the pancreatic duct from thepancreas meet the small intestine to releaseadditional enzymes to continue the process ofdigestion. From the duodenum, the mixturetravels to the jejunum and ileum, the otherStomachPancreasDuodenumFigure 13. Abdominal cavity showing the pancreas12
digestive system. The rabbit extracts additionalnutrients from the food this time, due to thefermentative changes that occurred in the cecum.Rabbits’ digestion exemplifies one type ofhindgut fermentation. Cattle and other ruminantsare called “foregut fermenters” becausemicrobial fermentation of their food occursbefore the food reaches the intestine.Although the rabbit colon can be divided intothe ascending, transverse, and descending colon,it is usually discussed in terms of the proximaland distal colon. A short, muscular portion calledthe fusus coli marks the division between thetwo. This section helps regulate the complexevents that move materials either forward orbackward and that determine whethercecotropes or dry feces are being produced. Thebeginning section of the proximal colon has alumpy appearance because it includes manypouches called haustra between longitudinalbands called taenia. The distal colon is a long,twisted tube that terminates with the rectum.Both dry feces and cecotropes exit the anus.Materials exit the small intestine through thesacculus rotundus to the large intestine—first toa short compartment called the ampulla cecaliscoli (a connection between the cecum and thecolon) and then to the colon. In the first section ofthe colon, the proximal colon, specialcontractions separate the more-digestible fromthe less-digestible materials and force thenutritious components backward into the cecum.The rougher materials continue along the distalcolon. The cecum is a large, coiled blind sac thatextends from the sacculus rotundus. The cecummakes up a larger proportion of the digestivetract in rabbits than in any other group ofanimals, and it is critical to the digestion of theirfood. Within the cecum, bacteria break down thematerial through fermentation. At certain times,material from the cecum is released to the colonwhere it is coated in mucus and excreted throughthe anus in the form of soft balls calledcecotropes, also known as night feces or softfeces. Rabbits immediately eat their cecotropes,and the materials pass again through theDistal colonHaustraColonTaeniaProximal colonCecumSacculus rotundusSmall intestineFigure 14. Abdominal cavity showing intestinal tract13Appendix
Dorsal Superficial Pelvic MusclesVentral Superficial Pelvic iform ligamentLiver, right central lobeOmentumTaeniaColonCecumRectumLiver, left central lobe10.11.12.13.14.15.16.17.18.Liver, left lateral lobeStomachSmall intestineAppendixEsophagusCystic ductGallbladderBile ductLiver, caudate lobeFigure 15. Stomach Pyloric stomachCardiac stomachSpleenPancreasIleumSacculus rotundusMesentery
Unit 5The Respiratory SystemTo view the respiratory system, open thethoracic cavity. Cut along the midline, from thediaphragm to the base of the neck. As you makeyour incisions, you will be cutting through somemusculature as well as the ribs. Fold back themusculature and ribs on both sides to expose thecavity. Pin the musculature down to expose thethoracic cavity.You have already examined the nares, theexternal portion of the rabbit’s nose. Rabbits areobligate nasal breathers; a rabbit cannot breathethrough its mouth due to the position of theglottis and epiglottis. These structures serve asthe opening of the respiratory system
Perform the dissection only on the dissection tray. Follow proper hygiene practices before, during, and after the lab. 2 Direction or Plane Definition Lateral Toward the right or left side Medial Toward the midline Proximal Near or toward the point of reference Distal Away from the point of reference Dorsal Toward the back Ventral Toward the belly
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