BIOL 204 W2024 Lab 5 TD1 PDF

Lab 5: The muscular system Objectives By the end of this week’s lab, successful students will be able to 1. Describe the structure(s) and function(s) of the muscular system. 2. Compare and contrast the three (3) different types of muscle tissue: a. Skeletal muscle, b. C...

Lab 5: The muscular system Objectives By the end of this week’s lab, successful students will be able to 1. Describe the structure(s) and function(s) of the muscular system. 2. Compare and contrast the three (3) different types of muscle tissue: a. Skeletal muscle, b. Cardiac muscle, and c. Smooth muscle. 3. Define the following terms: a. Origin, b. Insertion, c. Action, d. Agonist, and e. Antagonist. 4. Demonstrate how to use the following muscle action pairings: a. Adduct-abduct b. Flex-extend c. Protract-retract d. Elevate-depress e. Rotate 5. Discuss the four (4) different groupings of skeletal muscles and their origins: a. Branchiomeric, b. Hypobranchial, c. Axial, and d. Appendicular. 6. Identify muscles of the four (4) different muscle groupings between different vertebrate lineages, based on the embryological origins of skeletal muscle groups. 7. Discuss the relationship between the muscular system and the environment in which the organism is found in its native habitat. Important features to identify:  Horizontal septum, linea alba  Adductor mandibulae, intermandibularis, interhyoideus, mylohyoideus, cucullaris, masseter, temporalis, digastric, trapezius, sternomastoid  Latissimus dorsi, supracoracoideus, pectoralis, humeroantebrachialis, triceps brachii, biceps brachii, pectoral adductor, pectoral abductor  Coracoarcuals, rectus cervicus, sternohyoid  Epaxial, hypaxial, external oblique, internal oblique, transverse abdominus, rectus abdominus Introduction This is the first of three labs in which you will have access to three animals, the dogfish, mink, and pigeon. These three animals are chosen as representatives of aquatic, terrestrial, and aerial habitats. You will work on dissecting these animals in teams – roughly two people will work on an individual animal, and groups of approximately six students will work on at least two animals, 61 as due to supply chain issues, only one pigeon may be available in each lab. It is your responsibility to work as a cohesive lab group, such that everyone learns about each animal, and the appropriate comparisons between them. Not every animal will be equally easy to dissect and some labs will spend more time on one animal than another. You will need to work as a team to share the work load and ensure that you have equal time to view all three animals. Discuss your progress as you are performing the dissection: what your approach is, and how you could modify it if something is more complex or time-consuming than you expected. Although you and your dissection partner will usually dissect only one of the three vertebrates each week, you are responsible for learning and comparing the anatomy of all three vertebrates. Work together as a group to compare the anatomy of these three animals, to consider the function of each structure, and to discuss the questions in the lab manual. For example, if you are dissecting a dogfish, you are still responsible for learning the mink and pigeon. In this week’s lab, we will start the dissection portion of the course by looking at the external anatomy of the individual specimens, and the muscular system, which is responsible for the movement and locomotion of the organism. External Anatomy Dogfish (Squalus acanthias) 1. Note the overall shape of the dogfish and how it is streamlined for swimming. 2. Examine the fins: two dorsal fins (with spines, although the spines have most likely been trimmed off during the preservation process), one pair of pectoral fins, and one pair of pelvic fins, as well as the caudal fin, which forms the heterocercal tail. Figure 5.1. External features of Squalus acanthias. Image courtesy of UBC Vancouver. 62  3. Observe the pelvic fins. In males, claspers act as intromittent organs: they transfer sperm to the female during copulation for internal fertilization. Is your dogfish male or female? 4. The head has a ventral mouth, a pair of lidless eyes, a pair of spiracles, five pairs of gill slits, and a pair of nares. 5. Examine the surface of the head. Look at the ampullae of Lorenzini, which are fluid-filled pits that sense both depth (pressure) and low-level electrical stimuli. 6. Find the two endolymphatic ducts, which connect to the inner ear (an organ of equilibrium that senses the position and movements of the head). 7. Identify the lateral line along each side of body. It is used to sense vibrations and movements in the water. 8. Examine the cloaca, the chamber between the pelvic fins, and note the urinary papilla and anus. Pigeon (Columba livia) Pigeons have relatively large eyes (compared to the overall head size) as they rely on accurate vision for maneuvering during flight. 1. Look at the upper and lower eyelids and try to find the protective nictitating membrane (third eyelid). 2. Part of the external ear, the auditory meatus, is prominent, although covered by feathers. 3. Try to relate the external features of the pigeon to the skeletal system that we have already studied in lab. a. The carina (keel) of the sternum is obvious on the ventral midline of the chest. Trace this structure with your finger. b. Turn the pigeon onto its back and examine the wing – attempt to identify the regions of the wing that correspond to the i. humerus, ii. radius/ulna, iii. metacarpals, and iv. phalanges. c. Examine the hind limbs, locating the thigh (containing the femur), which is positioned tightly against the trunk. The most distal region of the hind limb is the foot. Mink (Neogale vison) The mink provided have already been skinned. You may still be able to notice some remaining tufts of hair, whiskers, as well as epidermal scales on the tail. 1. Observe the head, which has a mouth with lips. The nose has nares and the eyes bear upper and lower eyelids and a reduced nictitating membrane. The external ears (pinna) direct sound. 2. The trunk has an anterior thorax and posterior abdomen. 3. The anus is at the base of the tail, on the ventral side. 4. The urinary and genital openings are separate in females, but in males they run as one duct to the tip of the penis. Males have a large double pouch, the scrotum, which contains the testis. In the female, between the skin and muscles lies granular, mammary gland tissue in a band under the lines of nipples. 5. Determine the sex of your mink. 63 Muscular System Part I: Tissues of the muscular system While the muscular system is responsible for movement in the body, there are three (3) different types of muscular tissue that are each responsible for different types of movement in the body. 1. Examine the slides set up at the microscopes in the lab to see examples of the different types of muscles found in the body: a. Smooth muscle is responsible for movement inside the body, such as through the tubes of the digestive, respiratory, or cardiovascular system. Smooth muscle is often arranged in two adjacent layers, one that is wrapped around the tube circularly and one that is arranged longitudinally along the length of the tube. These muscles are under involuntary control. Smooth muscle cells have a single nucleus and the fibers intersect with one another. Smooth muscle tissue lacks sarcomeres (i.e., is not striated and therefore does not have multiple parallel bands running through it). b. Cardiac muscle is only found in the heart and, like smooth muscle, is under involuntary control. Cardiac muscle cells have single nuclei and are typically branched. Cells in muscle tissue are connected by intercalated discs and the tissue is striated, unlike smooth muscle tissue. c. Skeletal muscle is found throughout the body and is connected to bones via bands of connective tissue called tendons (remember the dense regular connective tissue examined in Lab 4, which also makes up the ligaments that connects bones to one another). Skeletal muscles are typically under voluntary control and are responsible for the locomotion of the body, as they work in conjunction with the skeletal system, like a series of levers. Skeletal muscle tissue is striated and the cells have multiple nuclei that are often pushed to the sides of the cells by the large amount of fibers along the length of the cell. These cells do not branch and are shaped like long cylinders. Our focus in this lab will be on the skeletal muscles. Part II: Terminology in the muscular system When discussing skeletal muscles, we need to use some specific terminology. Skeletal muscles work by contracting to bring the two ends of the muscle closer together. These two attachment points are referred to as the origin and the insertion. The origin is the attachment point that is more stable and immovable, while the insertion is the more mobile attachment point. When the muscle contracts, this generates the muscle action, which describes how the body moves. There are a variety of different actions that can be generated and these are arranged in pairs to describe the movement (see Table 5.1 below). 64 Actions are paired because muscles need to work together to regulate movement (remember that muscles can only contract on their own). Consequently, muscles work in agonist- antagonist pairs. An agonist muscle generates a specific motion, while the antagonist produces the opposite motion. Table 5.1. Skeletal muscle actions. Action Opposing action Abduction: movement away from the midline Adduction: movement towards the midline of of the body the body Flex: reduces the angle between two parts of Extend: increases the angle between two the body parts of the body Protraction: movement of part of the body Retraction: movement of the part of the body forward backward Elevate: raising the part of the body Depress: lowering the part of the body Part III: Embryonic origins of skeletal muscles Skeletal muscles originate from the myotome portion of the somites that run along the length of the body. While there are not somites in the head, there are somitomeres that perform the same function in this region of the body. The region of the body from which the skeletal muscles are derived can be very useful in distinguishing between different vertebrate lineages. All vertebrates have these somites but the functions of the muscles that derive from each region have changed over evolutionary time as different vertebrate lineages have adapted to life on land. Based on their position along the anterior-posterior axis, there are four (4) different groups of muscles that we will be discussing. 1. Branchiomeric muscles are derived from the most anterior somites and the somitomeres in the head and connect to the branchial arches of the splanchnocranium. In fish, branchiomeric muscles regulate movement of the jaw, hyoid arch and gills, whereas most of these muscles have been lost in mammals and those that remain are involved in the larynx and the shoulder 2. Hypobranchial muscles originate in the somites just posterior to the gills. During embryogenesis, these tissues extend anteriorly and ventrally to the regions between the gill slits and contribute to the axial muscles in the head. 3. Axial muscles come from the somites of the trunk to form the skeletal muscles of the trunk and tail. In gnathosomes, there are two major groupings, the dorsal epaxial muscles and the ventral hypaxial muscles, that are separate by the horizontal septum. 4. Appendicular muscles also originate from the somites of the trunk; however, these muscles connect to the pelvic and pectoral limbs. In sharks, these muscles simply adduct and abduct the pelvic and pectoral fins. In mammals, these muscles are much more complex, due to the presence of limbs with additional joints to articulate. This allows for more modes of locomotion. Typically, the appendicular muscles overlay the axial ones. 65 Part IV: Dissections When performing dissections, please be considerate and appreciate that we are using these animals to help us understand life on this planet that we share with these organisms. Be respectful for the sacrifice of these animals to help further your education in the field of biology. When performing dissections, you will be using a variety of tools from your dissection kits. For most of your dissections, you will typically only need the scissors, a teasing needle, a blunt dissecting probe, and the forceps (tweezers). For some procedures, you will need to use a scalpel. At these times, be very careful as these blades are very sharp.  Scissors will be used for most of the cutting part of your dissections. They can be used to cut off large chunks of fat or fascia and to reflect muscles. They can also be inserted between tissue layers and opened to cut overlying fascia.  Forceps can be used to remove smaller pieces of fat or fascia and to lift layers of fascia for removal or cutting with other tools.  The blunt dissecting probe can separate muscles from one another and penetrate multiple layers of fascia.  The teasing needle can be used to separate small muscles from one another and cut fascia. Prior to performing your dissections each week, please review the videos posted to Canvas to help prepare you for the dissections that you will be performing. 1. Together with your lab partner, join with another group to form a larger group of 4-6 students. This will be your dissection group for the remainder of the term. In this group, you will together dissect one spiny dogfish (Squalus acanthius), one mink (Neogale vison), and one pigeon (Columba spp).. Within your group, determine who will be focussing on each organism. While you and your lab partner are each primarily responsible for the dissection of one of the two organisms, you are expected to teach the rest of your group about your organism and learn about the other organism from the rest of your group. 2. Once you have determined your groups, notify your TA and collect your dissection tray, dissection mat, and animal. Dogfish Dissection 1. The first step in the dogfish dissection is to skin the region of the animal that we will be focussing on. Watch the video on Canvas and your TA’s demonstration of this technique. Watch this demonstration carefully before attempting to skin your dogfish, or you may damage the muscles. 2. Starting near the dorsal midline of the animal, use a scalpel to break through the skin of the dogfish. It’s a good idea to practice this near over the pelvic fin of the dogfish before doing this near the pectoral fin where we are interested in this. Use forceps to hold the edge of the skin and, pointing the scalpel down, carefully scrape the muscle and fascia off of the skin. 3. Once you have the hang of this procedure, start skinning the dogfish near the head of the animal. Start at the dorsal midline just behind the spiracle and work down to about 1 cm posterior of the pectoral fin. 66  4. Continue skinning onto the top of the pectoral fin, until you can see the ends of the pectoral abductor. Be cautious when working near the gills. 5. Remove the skin around the front of the gills and towards the ventral midline, just posterior of the jaw. Continue working posterior along the ventral surface to 1 cm behind the pectoral fin and skin along the ventral surface of the pectoral fin until you can see the end of the pectoral adductor. Once you have the dogfish skinned, you will be able to view the muscles in Table 5.2. For additional help, see Figures 5.2 and 5.3. Dogfish muscle origins Branchiomeric Muscles (colour red) The jaw muscles are associated with the first branchial arch. The adductor mandibulae, a large muscle below the spiracle, elevates Meckel’s cartilage (the lower jaw), closing the mouth. The intermandibularis is on the ventral surface, posterior to the lower jaw. It originates on the Meckel's cartilage and inserts on the central raphe (a raphe is a ridge of connective tissue). Its function is to elevate the floor of the mouth for swallowing. (The interhyoideus is another ventral constrictor muscle, but it is hidden by the intermandibularis so you will not see it in this dissection). A muscle of the hyoid arch, the levator hyomandibulae, can be located posterior to the spiracle. Its function is to elevate the hyomandibula, pulling it both dorsally and posteriorly. There are a variety of muscles associated with branchial arches III – VII (the five branchial arches that support the gills). These muscles generally function to move these branchial arches and the gills for ventilation. The most easily visible of these muscles is the cucullaris, which is located dorsal to the gills. The cucullaris elevates the scapular process of the pectoral girdle and also elevates branchial arches III - VII. Other muscles (constrictors, adductors and interarcuals) are located deep within and between the gills. Only the hyoid and superficial constrictors can be seen. Hypobranchial Muscles (colour green) The hypobranchial muscles form some of the muscles of the throat and jaws. The coracoarcual muscles are located ventral to the gills, attached to the coracoid bar of the pectoral girdle. They depress (lower) Meckel’s cartilage, opening the mouth. Axial Muscles (colour yellow) These are the segmental skeletal muscles of the trunk and tail – the myomeres. Myomeres are separated from each other by myosepta, which are sheets of connective tissue. (Myomeres are segmental blocks of axial muscle in the adult, which form from embryonic myotomes). The epaxial muscles are found dorsal to the horizontal septum and the hypaxial muscles are ventral to it. The ventral hypaxial muscles meet at the midline, forming a raphe (ridge of connective tissue) called the linea alba. Appendicular Muscles (colour blue) At the base of the left pectoral fin, locate the dorsal pectoral abductor muscle, and the ventral pectoral adductor muscle. What are the functions of these two muscles? 67 Figure 5.2. Lateral view of dogfish showing jaw, branchial and axial muscles. Images courtesy of UBC Vancouver. Figure 5.3. Ventral view of musculature in Squalus acanthias. Image courtesy of UBC Vancouver. 68 Table 5.2. Muscles of the spiny dogfish Muscle Location Action Branchiomeric muscles Adductor Below the spiracle and Elevate Meckel’s cartilage and closes the mandibulae around the lateral side of the jaw jaw Intermandibularis Caudal of the jaw along the Elevates the floor of the mouth (allows medial region of the ventral swallowing). surface Levator Posterior of the spiracle Elevate the hyomandibula (pulls dorsal and hyomandibulae posterior) Cucullaris Dorsal of gills Elevates the scapular process of the pectoral girdle and branchial arches III-VII Hypobranchial muscles Coracoarcual Cranial of the coracoid bar on Depress Meckel’s cartilage (open jaws) the ventral surface of the pectoral girdle Axial muscles Epaxial muscles Dorsal of horizontal septum Laterally bend the body Hypaxial Ventral of horizontal septum Laterally bend the body muscles Appendicular muscles Pectoral Extend from the dorsal Abduct the pectoral fin abductor scapular process to the dorsal side of the pectoral fin Pectoral Extend along the ventral Adduct the pectoral fin adductor surface of the body onto the ventral surface of the pectoral fin Mink dissection 1. The mink that you will be dissecting come from fur farms, so they have already been skinned; however, you will need to remove the external fascia in order to better view the muscles. Be cautious near the anus of the animal, as this the location of the scent glands (mink are mustelids: close relatives of skunk). 2. Examine both sides of your mink and determine which side of the animal is most intact from the head to just caudal of the forelimb. You will be cleaning up this surface of the animal. Remember to just focus on the regions where the muscles of interest are located. It is very easy to clean up more than you need. 3. Using the forceps to lift the fascia, a blunt probe to separate the fascia, and scissors to cut away larger pieces of fat or fascia so that you can see the following regions of the mink: a. along the lateral and ventral surfaces of the head b. along the lateral surface of the neck, from dorsal midline to ventral midline, 69  c. dorsal and ventral of the forelimb, and d. along the lateral and medial surfaces of the upper section of the forelimb (from the shoulder to the elbow). 4. Examine the ventral surface of the abdomen. The band of white connective tissue running along the midline is the linea alba, which is an attachment site for the hypaxial muscles of either side of the body. The darker coloured bands of muscle either side of the linea alba is the rectus abdominus, one of the four abdominal muscles. 5. Find a clean region of the abdomen along the lateral side of the abdomen, lateral to the rectus abdominus, and cut a three-sided square in the abdomen (folding down towards the linea alba. Using your forceps, gently pull apart the three (3) layers of the abdominal wall. You should be able to see the different orientations of the muscle fibers in each layer. Once you have cleaned these regions of the mink, you will be able to view the muscles listed in Table 5.3. For additional help, see the dissection guides and indicated available to examine in the lab. Mink Muscle Origins Branchiomeric Muscles (colour red) In the mandibular arch, the temporalis lies from behind the eye to the ear, occupying the temporal fenestra of the skull. It elevates the mandible (lower jaw). Behind and below the eye is the large masseter muscle, which elevates the jaw and allows for complex chewing. Ventral and medial lies the digastric muscle, which depresses the mandible. In the hyoid arch, the most important muscle in mammals is the sphincter coli, which is the posterior portion of the interhyoideus muscle. This muscle spreads onto the neck and becomes the platysma in mammals such as the rat (not examined here). It then spreads over the head and face to form the facial muscles of mammals such as humans, allowing a greater range of facial expressions. Because mammals lack gills, the muscles of the gill arches are mostly lost or reduced during development. Some muscles remain on the larynx and help with swallowing. The trapezius muscles of the pectoral girdle are homologous to the cucullaris muscle of the dogfish. The trapezius complex consists of three muscles, which originate on the vertebral column. Two insert on the scapula to adduct and move it dorsally and forward. The third muscle inserts on the clavicle and protracts the humerus. The sternomastoid muscle is also derived from the cucullaris muscle and serves to turn the head. Hypobranchial Muscles (colour green) In mammals, the hypobranchial muscles form the deep muscles of the throat and tongue. A hypobranchial muscle visible in this dissection is the sternohyoid, which originates on the sternum and inserts on the hyoid bone. It lies on top of the larynx. 70 Axial Muscles (colour yellow) In mammals, the axial muscles do not appear as obviously segmented as the myomeres seen in fishes and amphibians. Although in the embryo the myomeres of the axial muscles are easy to see, much of this segmentation is obscured or lost during development due to the growth of large and complex appendicular muscles. The epaxial muscles are long bundles that straighten and flex the body. These are deep muscles on either side of the vertebral column and are hidden by other muscles. The hypaxial muscles are composed of three sheets of muscles joined ventrally at the linea alba. On either side of the linea alba is a band of longitudinal muscle, the rectus abdominus, where the three muscle layers sit together in a common sheath. 71  Table 5.3. Muscles of the mink Muscle Location Action Dissection guide figure(s) Branchiomeric muscles Temporalis Caudal of the ear Elevates the mandible 3.6 Masseter Caudal of jaw Elevates the mandible 3.2-3.6 Digastric Ventral of masseter Depresses the mandible 3.2-3.5 Clavotrapezius Covers lateral and dorsal surface of Adduct the forelimb (move 3.4-3.7 neck dorsally and anteriorly) Acromiotrapezius Triangle-shaped muscle from dorsal Adduct the forelimb 3.6 midline to a point just anterior of the forelimb Spinotrapezius Posterior of acromiotrapezius Rotate scapula backwards 3.6 Sternomastoid Along ventral surface of the neck Rotates the head 3.2-3.5 Hypobranchial muscles Sternohyoid Ventral and deep of the digastric Depresses the hyoid 3.2-3.5 Axial muscles Rectus Lateral of the linea alba Compress abdomen, flex 3.14, 3.18 abdominus trunk External oblique Superficial layer of lateral abdomen Compress abdomen, flex 3.14, 3.18 trunk Internal oblique Medial layer of lateral abdomen Compress abdomen, flex 3.14, 3.18 trunk Transverse Deepest layer of lateral abdomen Compress abdomen, flex 3.18 abdominus trunk Appendicular muscles Latissimus dorsi “wing” along dorsal body just posterior Adduct forelimb at shoulder 3.4, 3.5, 3.6, of forelimb 3.8a Levator scapulae Ventral of acromiotrapezius. Muscle 3.6, 3.7, 3.8 ventralis fibers run along anterior-posterior axis. Clavodeltoid Caudal and ventral of clavotrapezius Flex humerus 3.4-3.7 Spinodeltoid Caudal of levator scapulae ventralis Abducts and flexes humerus 3.6 Acromiodeltoid Rounded muscle ventral of levator Protracts scapula 3.7 scapulae ventralis Triceps brachii Lateral and long heads on lateral Extend forelimb at elbow 3.6, 3.8 surface of forelimb from shoulder to elbow. Medial head on medial side of forelimb Brachialis Lateral side of forelimb on anterior side Flex forelimb at elbow 3.8, 3.10 of forelimb above elbow Biceps brachii Medial side of forelimb under pectoralis Flex forelimb at elbow 3.4, 3.11 Pectoralis major Upper portion of chest from ventral Adduct forelimb 3.4, 3.5 midline to forelimb Pectoralis minor Deep of and posterior of pectoralis Adduct forelimb 3.4, 3.5 minor 72 Pigeon Dissection See Figures 5.4-5.6 to assist your dissection. 1. Pluck (remove the feathers from) the entire chest area, from the most anterior point of the keel to the cloaca, taking care not to damage the delicate crop, which rests just anterior to the sternum. (It is okay if some skin comes off with the feathers since you will remove it in the next step anyway). 2. The skin should be easy to pull off as well - separate it from the underlying tissue using a blunt probe and try to apply consistent force as you pull the skin away from the muscles. Place the feathers and skin in the RED biological waste bucket provided. 3. Pluck the feathers and remove the skin from a wing to expose the biceps brachii and triceps brachii. See Figures 4. Pluck the feathers and remove the skin on the dorsal side on one half of the pigeon from the neck to the uropygial gland. From the beak down to the chest pluck very gently and pull the skin slowly (the crop is very close to the surface and is very fragile). 5. Remove the skin from one side of the head to see the jaw muscles. The jaw muscles are small and close to both the eye and the beak. 6. To make the pigeon easier to handle for the rest of the term, cut off all the remaining flight feathers from both wings, as close to the skin as possible without damaging the skin. 7. On the same side that the wing was plucked and skinned, make a cut through the pectoralis near its center. Cut at right angles to the fiber direction as that will be the direction of the fibers of the underlying supracoracoideus. Cut into the muscle a few millimeters at a time and spread the incision as you cut, to help avoid doing damage. 8. Once you find the supracoracoideus, you can cut out a large portion of the pectoralis to expose some of the supracoracoideus. Take caution when cutting through major blood vessels – they will be studied later, and a cleanly cut vessel is easier to study than a ripped and shredded vessel. Pigeon Muscle Origins Branchiomeric Muscles (colour red) Examine the muscles of the head. The mylohyoideus wraps around from the ventral part of the neck over the long, bony hyoid process. The masseter is just under this muscle, more anterior and dorsal to the mylohyoideus. The temporalis is more dorsal than the others, lateral to the eye. (The masseter and temporalis are often difficult to locate in the pigeon). The depressor mandibulae, as its name suggests, depresses (lowers) the mandible (lower jaw), opening the mouth. 73 Figure 5.4. Schematic (lateral view) of Columba livia jaw musculature. Image courtesy of UBC Vancouver. Axial Muscles (colour yellow) The large appendicular muscles obscure the view of most of the axial muscles in the pigeon. You can see the external oblique muscles posterior to the large pectoralis muscle. Many epaxial muscles are reduced in birds compared to in other tetrapods because of the fused vertebrae of the synsacrum. Dorsally, note the levator caudae, which elevates the tail. Appendicular Muscles (colour blue) On the wing, identify the biceps brachii and triceps brachii, as well as the large deltoideus (dorsal). On the dorsal side find the latissimus dorsi, originating on the midline, and the triangular teres major posterior to that. Both the upstroke (abduction) and downstroke (adduction) of the wing is powered by muscles located on the ventral side of the bird. This concentration of flight muscle mass allows for a lower center of gravity and therefore greater balance and stability during flight. The large pectoralis adducts the wings, providing the powerful downstroke needed for flight, while the supracoracoideus (which lies deep to the pectoralis), abducts the wing, producing the upstroke. 74 Figure 5.5. Ventral view of Columba livia musculature. Image courtesy of UBC Vancouver. It is easy to see how the pectoralis major can pull a wing down. But muscles can only contract - they never push. How can an antagonistic muscle located ventrally pull a wing up? The tendon that attaches the supracoracoideus to the dorsal surface of the humerus passes through an opening in the pectoral girdle that is located between the humerus, coracoid and the scapula. This is called the triosseal canal. When the supracoracoideus contracts, the whole system works like a pulley, raising the wing. 75 Figure 5.6. Dorsal view of Columba livia musculature. Image courtesy of UBC Vancouver. 76 Table 5.4. Muscles of the pigeon Muscle Location Action Branchiomeric muscles Mylohyoideus Ventral surface of neck Depress mandible inferior of beak Masseter Anterior and dorsal of Elevate mandible mylohyoideus Temporalis Lateral of eye and dorsal of Elevate mandible mylohyoideus and masseter Depressor Dorsal of temporalis Depresses or lowers the mandible mandibulae Hypobranchial muscles None examined Axial muscles External obliques Posterior of pectoralis Compress abdomen, flex trunk Levator caudae Dorsal side of body, posterior Elevates the tail of hindlimb and anterior of tail Appendicular muscles Pectoralis Ventral surface of body over Adducts the wing rib cage Supracoracoideus Deep of pectoralis Abducts the wing Biceps brachii Anterior side of wing, distal of Flex wing the shoulder Triceps brachii Posterior side of wing, distal Extend wing of the shoulder Deltoideus Anterior side of wing on Abducts the wing dorsal side of body Latissimus dorsi Dorsal side of body, Abducts the wing originating from the midline Teres major Posterior of latissimus dorsi Abducts the wing Once you have found the muscles in both the dogfish and mink, you can compare their locations with the homologous muscles in the other organism (Table 5.5; note that there are additional muscles listed in this table that you do not need to know). Make sure that you are familiar with both animals. 77 Table 5.5. Comparison of skeletal muscle groups in dogfish and mink. Based on information in Table 10.2 and 10.3 of Kardong (8th edition) and https://www.zoology.ubc.ca/~millen/oldvertebrate/eye.htm. Skeletal muscle Dogfish Pigeon Mink group Branchiomeric Adductor mandibulae Masseter Masseter Spiracularis Temporalis Temporalis Levator palatoquadrati Intermandibularis Mylohyoideus Mylohyoid Digastric (anterior) Interhyoideus Stylohyoid Digastric (posterior) Cucullaris Clavotrapezius Acromiotrapezius Spinotrapezius Cleidomastoid Sternomastoid Hypobranchial Coracoarcuals Sternohyoid Coracohyoid Axial Levator scapulae ventralis Serratus ventralis Epaxial muscles Hypaxial muscles Rectus abdominus External obliques Internal obliques Transverse abdominus Appendicular Pectoral abductors Latissimus dorsi Latissimus dorsi (pectoral) Teres major Teres major Subscapularis Deltoideus Clavodeltoid Acromiodeltoid Spinodeltoid Triceps brachii Triceps brachii Pectoral adductors Pectoralis Pectoralis major Pectoralis minor Supracoracoideus Supraspinatus Infraspinatus Biceps brachii Biceps brachii 78 Lab 5 assessment: Verbal quiz 5 marks; groups of 2-3 To be completed during next week’s lab period For this week’s lab, you will be assessed on the muscles that you have identified in the dissections completed by your lab group (both the dogfish and the mink) during next week’s lab period. 1. You and your lab partner(s) will be asked to identify ONE (1) muscle in each organism (THREE (3) muscles total). 2. Next, you will be asked to identify TWO (2) muscles that are homologous to the indicated muscles in the other organisms. For example, if your TA indicates the pectoralis major in the mink, the homologous muscle in the dogfish is the pectoral adductor (see Table 5.4). Discussion questions to help you prepare for the lab exam:  Compare and contrast the functions of the skeletal muscle groups indicated below in your dissected organisms. You must provide at least ONE (1) similarity (other than embryological origins) and ONE (1) difference for full marks. For the differences, be sure to describe what you are comparing in each organism. o Branchiomeric o Hypobranchial o Axial o Appendicular  Based on your answers to the question above, explain how the changes that you noted above help that organism survive in its particular environment. o Branchiomeric o Hypobranchial o Axial o Appendicular 79