2 Introduction (read this first) Welcome to cat dissection 2010! Each day will begin with logging on to your computer, putting on required protective gear, and removing your cat from the cat house. Attendance is taken immediately, so be here on time! Make this class a priority and do not come in late from your previous class or schedule lessons during this time. You are responsible for letting Mrs. V know if you are missing a teammate, so attendance can be recorded. Each day will end with the cat going back into storage, all unneeded/loose tissue going into a designated container, cleaning of the tools, sink, and table surface, thorough washing of hands, and return of all tools and protective gear to correct areas. You are to maintain a tidy work area. Personal items (books, notebooks, beverages, etc.) are to be left at your desk. Work diligently to get as much done each day as possible. Good luck!
3 Step 1: Get dressed. Use the following check list to judge your attire: shoes that cover your entire feetgoggles covering eyesglovesapronlong hair tied back
4 Muscles of the Lower Leg: 1. Show time!! Expect to be busier than a three-legged cat in a sandbox. Place your cat in the pronated position (on its belly). Locate the cat’s foot and heel. Make sure the skin is removed down to the heel. Attached to the calcaneus find a white, shiny, round band of dense connective tissue (c.t.) –the Achille’s tendon(39). 2. With a dull probe separate the Achille’s tendon from the surrounding tissue. 3. Two muscles are attached to the Achille’s tendon. Gastrocnemius(31) is the larger, superficial muscle on the posterior surface of the lower leg. The second calf muscle we will study is named the soleus(32). It can be identified by the following clues: a) it is attached to the Achille’s tendon; b) it lies beneath gastrocnemius on the lateral surface of the leg. (Warning: gastrocnemius separates into right and left “heads,” near the knee. Don’t mistake one of them for the soleus.) 4. Trace gastrocnemius up the leg. At the back of the knee, between the heads of the gastrocnemius and between two of the upper thigh muscles you will find a fat-filled pit at the back of the knee called the popliteal fossa. Clean the fat out of the fossa so that you can follow the heads of the gastrocnemius to the femur. 5. Place the cat into the supinated position. Locate the tibia at the anterior surface of the lower hind leg. Tibialis anterior(35) is a good sized, torpedo-shaped muscle lying just lateral to the tibia. A c.t. sheath (called a fascia) covers the muscle. Remove enough of the fascia to clearly see tibialis anterior and free its borders. Follow its tendon across the ankle to the medial side of the foot.
6 Superficial Muscles of the Medial Thigh: 1. With the cat in the supinated position, two superficial muscles can be viewed on the medial surface of the thigh. Sartorius (1) is a thin, flat muscle covering the anterior, medial surface of the thigh. It goes from the hip to the patella. Free its sides, lift it up and cut it in half, to allow viewing of the deeper muscles. 2. The other superficial muscle is named gracilis (8). It is similar to sartorius in shape, but covers the posterior medial surface of the thigh. It originates near the pubic symphysis and inserts on the lower leg below the patella. Free its border near the patella, so that the muscle can be folded back like a flap to expose the deeper muscles.
7 Deep Muscles of the Medial Thigh: 1. Semimembranosus is one of the three hamstring muscles. It is a large, thick, blocky muscle lying under gracilis. There is a natural deep split between it and the adjacent adductor femoris. On an average-sized cat, semimembranosus is about an inch wide from its anterior to its posterior border. Warning: A false split can often be made in the middle of semimembranosus or in the middle of adductor femoris.2. Next find two adductor muscles located on the medial thigh. The fibers of these muscles run from the pubic symphysis to the femur. Adductor magnus (femoris) is the wide muscle lying in front of semimembranosus. Adductor longus lies in front of adductor femoris. It is a narrow band of fibers, which can be traced to the anterior (and superior) tip of the pubic symphysis.
8 Muscles of the Anterior Thigh: The four deep muscles of the anterior thigh make up a group called the quadriceps femoris muscle group.The key to identifying the members of this group is to locate rectus femoris. This muscle runs from the hip to the patella, down the anterior surface of the thigh beneath sartorius. It is round and more or less cylinder-shaped.Once rectus femoris is located, vastus lateralis and vastus medialis are easy to find. They are bulky muscles lying lateral and medial to rectus femoris. They wrap around it, much like a bun wraps around a hotdog (rectus femoris being the “hotdog”).Vastus intermedius is tricky to locate because rectus femoris covers it up. Cut rectus femoris in half and pull back the ends. Vastus intermedius is just underneath rectus femoris. Vastus lateralis and vastus medialis are in contact with vastus intermedius on its medial and lateral borders. (The medial border separates poorly.) Push a probe through vastus intermedius. You should hit the femur underneath.SartoriusAdductor femorisTensor fascia lataeGracilisRectus femorisSemimembranosusVastus medialisPectineusVastus lateralisAdductor longusIliopsoasVastus intermedius
9 Muscles of the Posterior Thigh: 1. Return your cat to the pronated position. The three muscles at the back of the thigh arecalled the hamstring muscle group. The lateral hamstring muscle is called bicepsfemoris. This large, thick, flat muscle covers the lateral surface of the popliteal fossa. Itoverlaps the lateral head of the gastrocnemius muscle. Clean enough c.t. and fat off itssurface to find the anterior and posterior borders.2. At its posterior border, biceps femoris touches a second hamstring muscle,semitendinosus. This muscle is a long narrow muscle which passes from the hip region,along the medial surface of the popliteal fossa to the medial side of the lower leg. Separateout semitendinosus.3. The third hamstring muscle, semimembranosus, lies anterior and medial tosemitendinosus. This muscle lies under gracilis and was already identified along with themuscles of the deep medial thigh.1. sartorius6. caudofemoralis (not in humans)2. tensor fascia latae(probe under IT tract)7. gluteus maximus3. vastus lateralis8. gluteus medius4. biceps femoris9. semimembranosus5. semitendinosus10. gracilis
10 Muscles of the Hip and Butt: Locate the position of the greater trochanter (large protrusion from the proximal end of the femur) by moving the leg and pressing on the muscles. You should be able to feel it as a prominent bony bump. Superior to the greater trochanter find the iliac crest. Also locate the base of the cat’s tail. The gluteal (butt) muscles lie superior to biceps femoris between the tail, iliac crest and greater trochanter.Now that you know the general location of the muscles, you must remove the c.t. that obscures them. First, remove the c.t. and fat down to the shiny dense c.t. fascia that tightly covers all the muscles in this area. In order to really find the muscles, the fascia must now be removed. Do this by lifting up on the fascia and carefully cutting the fibers away from the backside of it. When you are done, you should be down to bare muscle fibers.If you removed the fascia completely, the muscles are fairly easy to locate. Gluteus medius is a large triangular muscle whose fibers run from the iliac crest to the greater trochanter. It lies lateral to the base of the cat’s tail and sacrum.Gluteus maximus lies along the inferior border of gluteus medius. It is a smaller muscle running from the base of the tail to near the greater trochanter.The final muscle found in this area is named tensor fascia latae. This thin muscle covers the lateral surface of the hip and blends into a sheet of c.t. called the iliotibial (IT) tract.1. sartorius2. tensor fascia latae with IT tract3. vastus lateralis4. biceps femoris5. semitendinosus6. caudofemoralis (not in humans)7. gluteus maximus8. gluteus medius9. semimembranosus10. gracilis
11 1. sartorius2. tensor fascia latae with IT tract3. vastus lateralis4. biceps femoris5. semitendinosus6. caudofemoralis (not in humans)7. gluteus maximus8. gluteus medius9. semimembranosus10. gracilis
12 The Deep Muscles of the Back: From the hip to the neck, the vertebrae and ribs are covered with a thick braided muscle called erector spinae. This is actually a group of muscles, but we will not learn them individually.This muscle group is deep to the shoulder muscles. It approaches the surface in the middle back where it is covered by a tough white sheath of c.t. called the lumbodorsal fascia. Remove a small strip of this fascia to get a peek at the erector spinae. The fascia is actually composed of two layers, so you will need to remove them both.
13 Muscles of the Abdominal Wall: Place the cat in the supinated position.Four flat, very thin muscles make up the abdominal wall. They are hard to identify unless you carefully observe the direction that the muscle fibers run.Down the middle of the abdominal wall from the sternum to the pubic symphysis locate a narrow band of c.t. which makes a white line called the linea alba. On either side of the linea alba lies a band-like muscle about one inch wide. This muscle is named rectus abdominis. It is attached to the lower ribs and sternum on one end and pubic bones at the other. The fibers in this muscle run lengthwise on the cat (from head to tail). To see the muscle fibers, remove a piece of the fascia covering the surface. Don’t waste your time cleaning the whole muscle.The second abdominal muscle we will find is called external oblique. It is the superficial muscle of the lateral abdominal wall. It can be found by cleaning c.t. and fat off the abdominal wall lateral to rectus abdominis. You can be sure you have it by the direction its fibers run. Starting from the lower ribs and upper back, the fibers wrap around the cat and pass down toward the pelvis at about a 45-degree angle.Look through all of the photos on the following slides, before proceeding. Also check out the demo-cat!
14 Begin by loosening the connective tissue with a dull probe, as shown. Be careful up here! Don’t remove chest muscles! Stay below the ribs.External obliqueConnective tissue and fat
15 In this picture, the triangle of loosened c. t In this picture, the triangle of loosened c.t. that the probe was under has been removed. The c.t. over rectus is hard to remove, so just do it in a small area,Rectus abdominisTransverse abdominisExternal oblique
16 External oblique is loosened and flipped back to show internal oblique External oblique is loosened and flipped back to show internal oblique. You do not need to expose as much of the muscles, as shown here, unless your c.t. happens to come off easily.Ribs-you don’t need to go up this far.
17 The muscle just deep to external oblique is cleverly called internal oblique. The easiest way to see it is to free the medial edge of the external oblique next to the rectus abdominis and peel external oblique back. The fibers of internal oblique run perpendicular to those of external oblique. The fibers of this muscle do not extend as far around the cat toward rectus abdominis as do those of external oblique.The last abdominal wall muscle lies underneath the internal oblique muscle even further off to the side. This paper-thin muscle, called transversus abdominis, can be found by carefully peeling back internal oblique. Its fibers run more or less across the abdomen perpendicular to those of rectus abdominis. If you can’t find it, look further off to the side.
18 Superficial Muscles of the Back Latissimus dorsi is fairly easy to find. It is a wide thin muscle that originates on the lumbodorsal fascia. Trace the muscle across the ribs and under the arm to where it is attached to the humerus. Warning: It often merges with the pectoralis muscles, a skin muscle, c.t. and fat, just behind the armpit. You will have to do a bit of careful scraping and cutting to expose this muscle.The cat has three trapezius muscles called clavotrapezius, acromiotrapezius and spinotrapezius. They are named from superior to inferior. All three originate along the midline on the spinous processes of the vertebrae.Clavotrapezius is a triangular-shaped thin muscle that originates at the back of the head and neck. It is said to insert on the clavicle. However, at the clavicle, the same triangular muscle mass simply changes names and becomes the clavodeltoid muscle. The border between the clavotrapezius and acromiotrapezius muscles consists of a fairly wide, clear c.t. partition. You should be able to find it if you carefully clean c.t. in the right area.1. External oblique2. Latissimus dorsi 3. Spinotrapezius4. Acromiotrapezius 5. Clavotrapezius 6. Levator scapulae ventralis 7. Spinodeltoid 8. Acromiodeltoid 9. Clavodeltoid10. Triceps brachii (lateral head11. Triceps brachii (long head)
19 Before finding the other trapezius muscles, you should locate some important landmarks on the scapula. By moving the arm, you should be able to locate the borders of the scapula under the muscles. Near the shoulder joint, you should be able to find feel a prominent, hard bump by pressing with your fingers. This bump is the acromion process. Running more or less inferiorly from the acromion process is a bony ridge on the scapula, the spine of the scapula. This ridge can also be located by pressing your fingers into the muscle. The acromiotrapezius muscle originates between the scapulae in a thin strong sheet-like tendon called an aponeurosis. (you may have already removed it). It inserts on the acromion process and the spine of the scapula. The spinotrapezius muscle is situated inferior to acromiotrapezius. It inserts on the inferior part of the spine of the scapula. It overlaps a part of latissimus dorsi. The border between spinotrapezius and acromiotrapezius is another indistinct c.t. partition.1. External oblique 2. Latissimus dorsi 3. Spinotrapezius 4. Acromiotrapezius 5. Clavotrapezius 6. Levator scapulae ventralis 7. Spinodeltoid 8. Acromiodeltoid 9. Clavodeltoid 10. Triceps brachii (lateral head 11. Triceps brachii (long head)
20 Superficial Muscles of the Shoulder: When you first look at your cat’s shoulder, you won’t see the muscles as they appear in the picture, because they are obscured by thick, close-fitting c.t. Clean away this c.t. down to the muscle fibers. Locate the spine of the scapula, acromion process, and clavicle, as they will serve as landmarks. Clavodeltoid has probably already been located, but find it again. This muscle is continuous with clavotrapezius. Clavodeltoid starts at the point where clavotrapezius leaves off, on the clavicle. Clavodeltoid passes over the shoulder joint out to the forearm. It shares a border with pectoralis major on the anterior surface of the cat’s arm. NOTE: This muscle is also referred to as clavobrachialis. Locate the acromion process. The acromiodeltoid muscle is a narrow triangular muscle that lies behind clavodeltoid. It has a narrow base near the acromion process and an insertion about halfway down the upper arm. The third deltoid muscle, spinodeltoid, is rather difficult to find unless you did a good job cleaning c.t. from the region of the spine of the scapula. The origin of this muscle is along the spine of the scapula. From there, it runs forward to contact the rear edge of the acromiodeltoid.1.Latissimus10.supraspinatus2.teres major11. levator scapulae (ventralis)3. infraspinatus12.clavotrapezius4.13.sternomastoid5.spinodeltoid14. acromiotrapezius6. Triceps long head15.spinotrapezius7. triceps lateral head8.acromiodeltoid9. Clavodeltoid (clavobrachialis)
21 Muscles of the ArmTriceps brachii has three divisions or heads. The long head is the large, thick muscle along the posterior surface of the arm. The lateral head is equally easy to find. It is a large thick muscle mass on the lateral surface of the arm anterior to the long head and inferior to spinotrapezius. The third, medial head, can best be found by cutting the lateral head and looking for a relatively narrow muscle wedged in between the lateral head, the long head and the humerus. Warning: the medial surface of the brachium is covered by a thin superficial muscle, epitrochlearis, so the medial head can’t be seen there. Remove and disregard epitrochlearis.Brachialis is a torpedo-shaped muscle closely associated with acromiodeltoid. It lies on the anterior lateral surface of the upper arm near the lateral head of triceps brachii. Clean c.t. and probe to find it.Biceps brachii lies on the anterior medial surface of the upper arm. To find it, flop your cat over on its back and move the pectoralis muscles toward the head. Look for another torpedo-shaped muscle, but one larger than brachialis.1. Triceps brachii (lateral head) 2. Triceps brachii (medial head) 3. Triceps brachii (long head) 4. Acromiodeltoid 5. Spinodeltoid 6. Clavodeltoid 7. Brachioradialis (omit)
22 Deep Muscles of the Scapula: Before you go on, cut the trapezius muscles, latissimus dorsi and the pectoralis muscles on the side so that you can explore the deep muscles of the scapula. It is suggested that you save the side you have already dissected and cut the other side. Three powerful deep shoulder muscles have the flat surfaces of the scapula as their origin. Locate the entire spine of the scapula. Move aside the cut trapezius muscles. Deep to acromiotrapezius, above the spine of the scapula, is a large muscle – supraspinatus (3). It fills the supraspinous fossa. If you probe through supraspinatus, you will hit the scapula beneath it. Pull down the cut edge of latissimus dorsi to expose the region below the spine of the scapula and find another thick muscle attached to the scapula. It is infraspinatus (4). It passes anteriorly to the humerus and deep to spinodeltoid. It fills the infraspinous fossa. Grab the scapula and rotate it out so the shoulder goes toward the chest. At the same time, bring the vertebral border of the scapula away from the spine. The purpose of this operation is to stretch out the rhomboid (11 & 12) muscles, which lie deep to acromio- and spino- trapezius. Their fibers run from the spinous processes of the vertebrae to the vertebral border of the scapula. (Hint: The vertebral border is perpendicular to the spine of the scapula.)
23 Deep ScapulaLocate the axillary border of the scapula. Teres major (6) is a chunky round, little muscle that runs along this border up to the humerus. If you look closely, you should be able to find the clear-cut separation between teres major and subscapularis. A probe pushed through supraspinatus, infraspinatus or subscapularis will hit the scapula. One passed through teres major will not, since it lies along the edge of the scapula, not on its surface.While the cat is on its back, find serratus ventralis (4). This muscle has several finger-like divisions that attach to several of the lower ribs. Its superior end is attached to the inferior point of the scapula. Fat often obscures the “fingers” of this muscle and must be removed to see them.Now, flip the cat over on its back and flop its arm and scapula out. The under surface of the scapula, that is normally next to the ribs, is covered by subscapularis (5), which fills the subscapular fossa.
24 PectoantebrachialisPectoralis MajorPectoralis MinorXiphihumeralis (not in humans)Linea albaEpitrochlearisTriceps Brachii (long head)Teres MajorSubscapularisSerratus Ventralis (anterior in humans)Latissimus Dorsi
25 Superficial Chest Muscles: These muscles are hard to dissect because they are thin, overlapping and are joined tightly together by connective tissue. First, find the sternum from the manubrium to the xiphoid process. The chest muscles originate on the sternum.Second, move the cat’s arm around to locate its elbow, shoulder, and humerus. The chest muscles insert along the front of humerus.Now, on one side only, clean off the c.t. right down to the muscle fibers. Next, it’s time for a little feline massage. Give the cat a good rubdown with a paper towel to dry the chest. If you do this thoroughly, you should be able to locate the faint white “cleavage lines” where the muscles come together.The superior border of the pectoralis major (3) is in contact with clavodeltoid. The border begins at the tip of the manubrium and runs out the arm. Locate the cleavage line and separate these two muscles with careful pulling and cutting. You will also loosen a cat muscle called pectoantebrachialis (4) , that lies over this area.Now we will look for the hard-to-find cleavage line between pectoralis major and pectoralis minor. Look for it along the sternum about three inches below the superior border. At this cleavage line, pectoralis minor “dives” under pectoralis major so the separation you make will go down and forward under pectoralis major. A warning: inferior to the true pectoralis major/pectoralis minor cleavage line, there is often a false cleavage plane that will split pectoralis minor in two. You will know you have the wrong cleavage plane if it goes in and back instead of in and forward.Pectoralis minor lies deep to pectoralis major. Trace it forward to the humerus. Its inferior border is a fairly distinct line where it makes contact with a muscle we will not dissect, xiphihumeralis (1). The superior border of pectoralis minor lies beneath the body of pectoralis major, about halfway toward the head. This edge can be found by probing under pectoralis major.
27 Muscles of Chewing:Clean the skin off one side of the cat’s head as far forward as the eye, as far backward as the external auditory meatus (remove the external ear), as far up as the middle of the top of the head and as far down as the mandible. Try not to damage nearby structures such as the salivary glands (see photo on next slide).Now locate the zygomatic arch by probing. It runs all the way from just below the eye back to the external auditory meatus. Clean the c.t. and fat off all the way down to bare bone and muscle.The masseter muscle can now be found lying inferior to the zygomatic arch. Its upper end attaches to the arch and its lower end goes around the edge of the mandible to attach to the inside.The temporalis muscle originates on much of the side of the cat’s head and passes underneath the zygomatic arch to insert on the mandible. Starting near the top of the head, remove c.t., fat, and superficial skin muscles until you can see the glistening sheath covering temporalis. Trace the muscle down to where it passes beneath the zygomatic arch.
30 Muscles of the Floor of the Mouth: Remove the thick layer of c.t. covering the floor of the mouth (the area under the chin lying between the two halves of the mandible).The digastric muscles are narrow bands of muscle that lie along side the inner surface of the mandible. Their fibers run parallel to the mandible.The mylohyoid muscle makes up the floor of the mouth. Its fibers originate on the mandible and run toward the midline to meet there. The lateral edges of mylohyoid are deep to the digastric muscle and can be separated from it with a dull probe.DiagastricMylohyoidOmitSternohyoidSternomastoidClavotrapeziusMasseterCleiodmastoid
32 Muscles of the Anterior Neck Region These muscles should be dissected on the side of the cat from which you removed the ear. The landmarks we will use to find these muscles are the external auditory meatus, the mastoid process behind it, the sternum, and the clavicle. The cat’s clavicle is a tiny bone about the size of a paper match. It lies between the shoulder and sternum buried in muscle. Pinch the muscle in this area to locate the clavicle.The sternomastoid muscle is a strap-like muscle that runs on the surface of the neck from the mastoid process to the superior top of the sternum. Unfortunately, this muscle is obscured from view. At the upper end, a salivary gland and blood vessels get in the way. The middle part is crossed by a large vein. The entire neck region is covered by an especially thick layer of c.t. Remove the c.t. from the surface of the muscle and from between the muscle and the blood vessel and salivary gland. Once the anterior border of the muscle is free, start to work your way underneath with a dull probe. Also, work beneath the muscle from the posterior border until you have freed the muscle from mastoid process to sternum. (Warning: Just above the sternum there is often a confusing set of cross fibers which run from the right to the left across the sternomastoid muscle. You can safely remove these fibers.)The cleidomastoid muscle lies deep to the sternomastoid muscle. Trace it from the clavicle to the mastoid process. Separate the sternomastoid and cleidomastoid using a dull probe.