GENBIO2 Lab Module 6 Worksheet PDF

Page 1 of 7 The skeleton is an essential part of the body of every vertebrate animal. It has several functions: (1) serves as support or framework for the softer parts of the body, (2) provid...

Page 1 of 7 The skeleton is an essential part of the body of every vertebrate animal. It has several functions: (1) serves as support or framework for the softer parts of the body, (2) provides a firm surface for the attachment of muscles used in movement and locomotion, (3) supplies calcium to the blood, and (4) important site in the formation of blood cells. MODULE There are two types of skeleton: the exoskeleton 6 and the endoskeleton. The exoskeleton of vertebrates consists of the hardened bony or horny structures that develop in the skin and provides external protection to the animal. These structures are poorly developed in frogs/toads. The skeleton of the frog/toad is almost entirely endoskeletal in nature and consists almost entirely of bone and cartilage. MUSCULO- Skeletal muscles and skeleton are often SKELETAL considered together as a functional unit that permit body movements and locomotion. Muscles are attached to the SYSTEM bones by a connective tissue called tendon. A broad, flat and sheet-like tendon is called aponeurosis. Skeletal muscles often have two points of attachment. The part in between is sometimes referred to as the belly of the muscle. Locating the attachments can facilitate identification of a muscle. Other clues to identify muscle include the shape and relative size of the muscles, direction of the muscle fibers, as well as the action of the muscles. It is worthwhile to note that these factors mentioned are also the bases for naming muscles. Objectives At the end of the activity, the student should be able to: 1. identify selected bones of the toad and the functions of major bones. 2. to dissect and identify major muscles of the toad. Materials Preserved toad skeleton Dissecting materials Dissecting pan Preserved toad  Page 2 of 7 A. Gross Anatomy of the Toad Skeleton 1. Secure a prepared skeleton of a toad. 2. Use a probe or needle in pointing. Handle the prepared skeletons carefully as they are brittle and delicate. 3. Identify the structures based on the divisions described below. Label the photographs in the activity sheet. Divisions of the endoskeleton according to position in the body: a. Axial endoskeleton– composed of all endoskeletal structures located at the center or axis of the body. 1. Skull 2. Visceral skeleton 3. Vertebral column and ribs (it lacks true ribs) 4. Sternum b. Appendicular endoskeleton– consists of all endoskeletal structures located laterally or in the region of the extremities or appendages. 1. Girdles Pectoral girdle Pelvic girdle 2. Bones of the limbs Anterior limbs or forelimbs Posterior limbs or hindlimbs The Skull. The skull of the frog is flattened dorsoventrally. It is wider posteriorly and narrower anteriorly. It encloses the brain and the sense organs. It includes the cranium or braincase and the visceral skeleton (jaws, hyoid apparatus, and bones of the ears). Detach the skull of the toad and examine the following parts: Dorsal View of the Skull a. Locate a pair of flat, triangular-shaped bones on the dorsal surface of the skull just behind the nares. These are the nasal bones. b. The frontoparietals are two long, slender, flat bones, just posterior to the nasal bones. These may be fused so that they appear as a single bone. The frontoparietals cover most of the brain. c. At the posterior end of the skull is a large opening, the foramen magnum, through which the spinal cord passes. d. Surrounding the posterior part of the brain is a bone called exoccipital. A pair of prominent bones project from the exoccipital. These are the occipital condyles. e. The upper jaw is formed by the premaxillae, the maxillae, and the quadratojugals. The premaxillae are paired, short, teeth-bearing bones that form the anterior most edge of the upper jaw.  Page 3 of 7 f. The maxillae are paired curved teeth- bearing bones, forming the margin of the jaw. These are the longest bones of the upper jaw. These are wide in front where the premaxillae articulate. g. Short bones make up the posterior part of the upper jaw, but unlike the premaxillae and maxillae, these do not bear teeth. These are the quadratojugals. h. Extending upward from these bones are the squamosals, each shaped in the form of a hammer and serves as a brace between the cranium and the posterior portion of the jaws to support the cartilaginous auditory region. i. Notice the two large openings, the orbits or eye socket, lateral to the frontoparietals, where the eyeballs are located. Ventral View of the Skull a. The vomers are two flat, wing-shaped bones in the roof of the mouth just posterior to the premaxillae. The ventral surface of each bears the vomerine teeth. b. Locate the slender, rod-like bones on the lower side of the cranium just posterior to the vomers. These are the palatines. They extend laterally from near the median line to the maxillae. c. The dagger-shaped parasphenoid is a single bone that forms the floor of the cranium. Cartilages form the sides of the cranium. Visceral Skeleton The visceral skeleton is the endoskeletal structure derived from the gill arches and in the frog, it consists of (a) the upper and lower jaws, (b) hyoid apparatus that provide support for the muscles used in respiratory movements of the mouth, and (c) the cartilages that support the ventral wall of the larynx or voice box. The Vertebral Column a. The vertebral column of a frog is very specialized, due to the shortening of the trunk of the body. There are ten vertebrae that make up the vertebral column. b. The first vertebra or atlas is specialized for articulation with the skull by means of two large facets or depressions, which receive the occipital condyles of the skull. Notice that the atlas lacks transverse processes which are present on all other vertebrae. These processes, which represent fused ribs, support the attachments of muscles. c. The vertebral column is continued beyond the sacral region by the urostyle, which represents several fused tail or caudal vertebrae. The urostyle has a conspicuous dorsal keel, and a hollow canal, best seen from the anterior end, into which the spinal cord continues.  Page 4 of 7 The Pectoral Girdle The pectoral girdle (shoulder girdle) consists of a series of bones and cartilages which encircle the body and provide support for the forelimbs. In the toad, the pectoral girdle is firmly attached to the sternum or the breastbone. The Pelvic Girdle The pelvic girdle supports the hindlimbs. It consists of two identical halves, one half of which is called an innominate bone. Bones of the Forelimbs Study and identify the bones of the anterior limbs. a. The bone of the upper arm is the humerus. b. Radioulna represents the fusion of two bones, the radius and ulna of other land vertebrates. The proximal end of the radio-ulna is extended into a process, known as the olecranon, which reaches around the distal end of the humerus and serves for the attachment of muscles. c. The carpals are the bones of the wrist. d. The metacarpals or bones of the hand proper consist of four slender bones of the palm to which the phalanges or smaller bones of the digits or fingers are attached. Bones of the Hindlimbs Study and identify the bones of the posterior limbs. a. The bone of the thigh is the femur. b. Tibiofibula also represents the fusion of two bones, the tibia and fibula of most land vertebrates. c. The tarsals, or anklebones, corresponding to the carpals of the wrist. The two proximal tarsals are greatly elongated thus giving the hindlimb an extra segment and an extra lever arm; these two are the medial tibiale or astragalus and the lateral fibulare or calcaneus (the stouter of the two, opposite the fibula). There are also four additional distal tarsal bones. d. The metatarsals consist of five long bones of the sole to which the smaller bones (phalanges) of the digits are attached.  Page 5 of 7 B. Skeletal Muscles of the Toad 1. Skinning the specimen. a. Obtain a preserved toad/frog and rinse off excess formalin with tap water. Place the specimen ventral side up on a dissecting pan. b. With the use of a scissor, make a mid-ventral slit on the skin of the specimen from the posterior end of the trunk up to the tip of the lower jaw. Be sure that the pointed ends of the scissors are directed upward while making the slit to avoid injuring the underlying muscles. c. Make a transverse cut around the body just above the hindlimbs, and another one anterior to the forelimbs. d. Carefully remove the skin of the trunk and pull off the skin of the hindlimbs and forelimbs, inner side out. e. Remove the skin of the head around the eyes. In toad, the skin covering the head can be removed but with difficulty. f. Notice the large spaces between the skin and muscles where the skin is not attached. These are the subcutaneous lymph sacs. 2. Important hints for dissection to separate the muscles of the toad/frog. a. Dissection of the muscles requires separating the muscle bundles from each other. Separation of the muscles involves observing the direction of the fibers and the extent of the muscle. b. Never use sharp instrument like scissors or scalpel in separating them. Use instead the blunt end of an instrument to loosen the muscle tissues. c. DO NOT CUT muscles unless instructed to do so. If necessary to cut superficial muscles to find deep muscles, cut through the belly of the muscle. 3. Identification of the muscles. Locate and identify the muscles based on the description given. The given description fits both the frog and toad. Nonetheless, anatomical differences, if any on specific muscles will be noted. Label the photographs in the activity sheet. Ventral Muscles of the Head and Trunk Place the toad ventral side up on the dissecting pan. Locate the following muscles: a. Mylohyoid– locate the median longitudinal connective tissue on the ventral side of the lower jaw. This connective tissue is called the median raphe. Lateral to the median raphe is the thin broad, transversely oriented fibers of the mylohyoid.  Page 6 of 7 b. Sternoradialis– find this thick median pair of muscles which is partly covered by the posterior rim of the mylohyoid. c. Cutaneous pectoralis– locate this most ventral, thin, pocket like superficial muscle. d. Pectoralis– deflect ventrally the cutaneous pectoralis and locate a group of fan-shaped muscles also found posterior to the sternoradialis. This is the pectoralis and can be seen divisible into three parts: anterior, middle, and posterior pectoralis. e. Rectus abdominis– identify the thin connective tissue running at the mid- ventral portion of the abdomen. This is the linea alba. Lateral to the linea alba is a longitudinal muscle called the rectus abdominis. f. External oblique– find the sheet like muscle lateral to the rectus abdominis. Notice that the direction of muscle fibers ran obliquely. Ventral Muscles of the Thigh and Shank a. Sartorius– locate this flat strap-like muscle running obliquely along the ventral side of the thigh. b. Adductor longus– This is a slender muscle that can be seen by cutting the belly of the sartorius. c. Adductor magnus– find the thick muscle near the groin area, seen as a triangle when the sartorius is in place. This is also the muscle immediately posterior to the adductor longus. d. Gracilis major– locate this large muscle with oblique fibers situated posterior to the adductor magnus. e. Gastrocnemius– locate this large muscle situated at the back of the shank. Note the white tissues (fascia) surrounding the belly of this muscle. f. Tibialis posticus– find this long, narrow but thick muscle anterior to the gastrocnemius and partly covered by it. This is seen attached to the surface of the tibiofibula. g. Tibialis anticus– locate the most anterior muscle of the shank which can also be seen dorsally. This muscle splits into two distally. Dorsal Muscles of the Head and Trunk Turn the specimen dorsal side up and identify the following muscles: a. Longissimus dorsi– find the mass of muscle lying alongside the mid-dorsal line and tapering posteriorly. b. Iliolumbaris– locate the muscle lateral to the longissimus dorsi. The lateral or horizontal skeletogenous septum, a strong connective tissue, separates the iliolumbaris from the lateral external oblique. c. Coccygeo-iliacus– locate a pair of large V-shaped muscles situated between the ilia of the pelvic girdle.  Page 7 of 7 Dorsal Muscles of the Thigh and Shank a. Triceps femoris– this is the largest, three-headed muscle that covers the lateral surface of the thigh. b. Gluteus– find this small but thick muscle found between the two heads of the triceps femoris. c. Biceps femoris or Iliofibularis– locate this slender muscle posterior to the triceps femoris. d. Semimembranosus– this large muscle is found next to the biceps femoris. e. Gastrocnemius (as previously described) f. Peroneus– locate this muscle of the shank immediately anterior to the gastrocnemius and partly covered by it. g. Tibialis anticus (as previously described) Store the dissected toad in a container containing 10% formalin. This will be used in the next activity. References Abramoff, P., Thomson, R. 1986. Laboratory Outlines in Biology IV. W.H. Freeman and Company, New York. 81-89. Burns, R., Stiles, K. 1977. Laboratory Explorations in General Zoology. 6th ed. MacMillan Publishing Co., Inc. New York. 243-255. Duran, A.P. 1987. Laboratory Manual in General Zoology. A.P. Duran Enterprises. Elliott, A. 1974. Laboratory Guide for Zoology. 5th ed. Burgess Publishing Company, Minneapolis, Minn. 131-135. Gunstream, S. 1993. Explorations in Basic Biology. 6th ed. MacMillan Publishing Company, USA. 110-227. Hickman, C.P., F.M. Hickman and L. Kats. 1997. Laboratory Studies in Integrated Principles of Zoology. 9th edition. The McGraw-Hill Companies, Inc. pp. 251- 265. Minkoff, E. 1975. A Laboratory Guide to Frog Anatomy. Pergamon Press, Inc. USA. 1- 14. Pahl, George, FSC. 1987. Principles of Zoology Investigations. De La Salle University Press, Manila.