Source of content: general zoology lab guide.
Operation method
Experiments on the appearance and anatomy of frogs
Principle
1. to grasp the main features of amphibians through the observation of the appearance and anatomy of frogs (or toads), and to understand the initial structural and functional adaptations to terrestrial life exhibited by amphibians in the transition from aquatic to terrestrial life of vertebrates. 2. to learn how to dissect frogs (or toads).
Materials and Instruments
Live frogs Frog skin sections Skeletal specimens Move I. Shape Common Problems I. Assignment 1. Mapping
Anatomical disks Large head pins Dissecting instruments Microscopes
Live frogs (or toads) are placed in a dissecting dish and their bodies are observed, which can be divided into 3 parts: head, trunk and limbs.
1. Head
The head of the frog (or toad) is flat, slightly triangular, with a slightly pointed muzzle.
The mouth is wide and transverse, consisting of upper and lower jaws. There is an external nostril at the dorsal front of the maxilla and a nasal valve at the outer edge of the external nostril. Observe how the nasal valve moves and think about how the movement of the nasal valve is related to the movement of the floor of the mouth.
Eyes large and prominent, on right and left sides of head, with upper and lower eyelids; lower eyelid with a translucent transient membrane on inner side.
Lightly touch the eyelids and observe whether and how the upper and lower eyelids and the transient membrane move. How does the position of the eyeball change when the eyelid is closed?
There is a round tympanic membrane behind each eye (the tympanic membrane is smaller in toads. Behind and above the eyes and tympanic membrane there is a pair of oval-shaped elevations called postauricular glands, i.e., venom glands).
In male frogs, there is a light brown membrane fold at the back of each corner of the mouth for the vocal sac, which bulges into a bubble when calling (toads do not have this structure).
2. Carapace
After the tympanic membrane is the carapace. The frog's trunk is short and wide, and there is a small hole in the back of the trunk, between the two legs, on the dorsal side, for the cloaca.
3. Limbs
The forelimbs are short, consisting of the upper arm, forearm, wrist, palm and fingers. 4 fingers, no webbing between fingers.
During the reproductive season, male frogs (or male toads) have an enlarged protuberance on the inside of the base of the first finger, which is called the nuptial tumor and is used for holding pairs.
The hind limbs are long and well-developed, divided into femur, tibia, tarsus, metatarsus, and toes.5 toes, with webbing between them. There is a hard, keratinized spur on the inside of the first toe.
The hind limbs play a major role in which movement of the frog?
Toads have short blunt limbs, shorter hindlimbs than those of frogs, and poorly developed webbing between the toes. Do these features make the toad good at jumping and swimming?
Skin
Frogs have rough skin on the back, often with a narrow and light-colored longitudinal stripes in the center of the back, and a light-colored dorsal fold on each side.
The dorsal skin color varies greatly, with yellow-green, dark green, gray-brown, etc., and irregular black spots. The ventral skin is smooth and white.
The body surface of the toad is extremely rough, with rounded scrobes of varying sizes, but the dorsal surface of the head is free of scrobes. Dorsal dermal limbs dark black, lateral and ventral sides light yellow, interspersed with black patterns.
1. The skin of the living frog is slippery when touched with the hand, and the mucus is secreted by the skin glands.
What is the significance of keeping the skin moist for the life of the frog?
2. A microscopic examination of a section of frog skin shows that the skin consists of epidermis and dermis.
The stratum corneum is exposed on the surface of the body, is extremely thin and consists of flat cells (what is the purpose of the thicker stratum corneum in toads?) Underneath the stratum corneum is the hair layer made up of columnar cells.
There are also openings for glands and a few pigmented cells in the surface layer.
The dermis is located below the epidermis, its thickness is about three times that of the epidermis, composed of connective tissue, can be divided into the loose layer immediately below the epidermal hair layer and the dense layer below it. There are many pigment cells, multicellular glands, blood vessels and nerve endings in the dermis.
3. Note the extent to which the skin is connected to the subcutaneous muscles. Is the skin richly vascularized? What is the significance?
Skeletal system
The skeletal system of the frog (or toad) consists of the median skeleton (including the skull and spine) and the appendicular skeleton. The following observations should be made on the skeletal specimens of frogs (or toads).
1. Skull
The skull of the frog (or toad) is flat and wide, and can be divided into two parts: the cranium and the pharynx.
(1) Cranium
The central narrow part of the cranium is the skull, which is the place to hold the brain marrow; there is a large space on each side of it, where the eyeballs are born.
At the posterior end of the skull there is the foramen magnum of the occipital bone, through which the brain communicates with the spinal cord. Observe the bone fragments that make up the cranium.
(1) From the back
External occipital bones: 1 pair, located at the back of the last, right and left ring, through the foramen magnum of the occipital bone, each external occipital bone has a smooth rounded protuberance, called the occipital condyles, and the cervical vertebrae associated with the joints.
Anterior ossicles: 1 pair, located on the anterolateral aspect of the two external occipital bones.
Frontal parietal bones: 1 pair, long and narrow, located anterior to the external occipital bones, forming the main part of the parietal wall of the cranium.
Nasal bones: 1 pair, located anterior to the frontoparietal bones, slightly triangular in shape, forming the dorsal wall of the nasal cavity.
Pterygoid sieve bones: located between the nasal bones and the frontoparietal bones, they form the anterior wall of the cranial cavity. It extends forward and forms the posterior half of the nasal cavity. This bone is visible on the ventral surface of the cranium.
②Visualized from the ventral surface
Parasphenoid bone: the largest flat bone on the ventral surface of the skull, slightly "+" shape, its posterior edge and the outer occipital bone, in front of the pterosphenoid bone.
Plow bones: 1 pair, located in the ventral surface of the nasal capsule. There is a cluster of fine teeth on the ventral surface of each plow bone in frogs, which is called plow bone teeth (no plow bone teeth in toads).
(2) Pharyngeal Cranium
Includes the bones that make up the upper and lower jaws and the hyoid bone.
Maxillae
Pre-maxillae: 1 pair, short and small in shape, located at the front end of the maxilla, with teeth on the lower edge (toads do not have pre-maxillary teeth).
Maxillae: 1 pair, long and flattened, connected to the premaxilla at the anterior end, and adjoined to the square yoke bone at the posterior end, forming the outer edge of the maxilla. The lower surface of each bone is sunken into a groove, and the outer edge of the groove bears neat fine teeth, called maxillary teeth (toads do not have maxillary teeth).
Square yoke bones: 1 pair, short, located on either side of the outer edge of the posterior end of the maxilla, attached to the maxilla. Its posterior end is a piece of square cartilage that has not yet ossified.
Squamosal bones: 1 pair, located on both sides of the preauricular bone, "T"-shaped. Its main branch extends posteriorly and laterally to connect to the posterior end of the square yoke bone, and the posterior end of its transverse branch connects to the preauricular bone.
Pterygoid bones: 1 pair, located below the squamosal bones, in a "herringbone" shape. Its anterior branch is adjacent to the middle portion of the maxilla, and its posterior and medial branches are connected to the cuboidal cartilage and anterior ossicles, respectively.
Palatine bones: 1 pair of transverse elongated bony rods, located on the ventral surface of the skull, connected to the pterygoid sieve bone at one end and to the maxilla at the other end.
②Mandibular bones
Yi bone: 1 pair, very small, located at the anterior end of the jaw.
Mackerel's cartilages: 1 pair of rod-shaped cartilages that form the middle axis of the mandible; their posterior ends widen to form an articular surface that is articulated with the square cartilage of the maxilla. However, when specimens are made, this bone is often absent, leaving only a longitudinal groove.
Dentary bones: 1 pair, long thin sclerotized pieces, attached to the outside of the anterior half of the cartilage of the maxillae.
Coracoid bones: 1 pair, large, enclosing the inner and lower surfaces of the Maier's cartilage. The anterior end is attached to the odontoid bone, the posterior end widens and extends to the articulation of the mandible.
(iii) Hyoid bones
Located at the floor of the mouth, it is a group of bones that support the tongue. It consists of a flattened, nearly rectangular body of the hyoid bone and a pair of anterior horns at its anterior end and a pair of posterior horns at its posterior end.
2. Spine
The spine of the frog (or toad) consists of 1 cervical vertebrae, 7 trunk pivots, 1 sponsor vertebrae and 1 caudal rod bone.
(1) General structure of the vertebrae
Take 1 trunk vertebra and observe it.
①Vertebral body
It is the thickened part of the ventral surface of the vertebrae.
It is concave at the anterior end and convex at the posterior end, making it an anteriorly concave vertebra.
The concave and convex surfaces of neighboring vertebrae anterior and posterior are articulated with each other.
The vertebrae of the last trunk vertebra of the frog are biconcave (the vertebrae of each trunk vertebra of the toad are anteriorly concave).
②Vertebral foramen
An oval-shaped hole in the back of the vertebrae. The foramina of the neighboring vertebrae in front and behind are connected to form a canal, the spinal canal, through which the spinal cord runs.
③Vertebral arch
A pair of curved pieces of bone on the dorsal side of the vertebral body, forming the top and side walls of the foramen.
④Vertebral spine
A short protrusion in the center of the back of the arch.
⑤Transverse process
A pair of long projections protruding outward from the sides of the vertebral body at the junction of the base of the arch and the vertebral body.
(6) Articular process
2 pairs of small projections located at the anterior and posterior margins of the base of the vertebral arch.
The anterior articular process faces forward and is called the anterior articular process; the posterior articular process faces backward and is called the posterior articular process. The posterior articulation of the anterior vertebra is associated with the anterior articulation of the posterior vertebra.
(2) Cervical Vertebra
It is the first vertebra, also called atlas. The atlantoaxial vertebra has no transverse process and anterior articular facet, but has two oval concave surfaces in front of it, which are associated with the occipital condyles of the skull.
(3) Sponsor Vertebra
It has a long, flattened transverse process that extends backward and articulates with the anterior end of the ilium. The posterior end of the vertebral body has 2 small rounded projections, which are associated with the anterior end of the coccyx.
(4) Caudal rod bone
It is an elongated rod-like bone formed by the healing of several caudal vertebrae. It has 2 concave surfaces at its anterior end, which are articulated with two projections at the posterior end of the sponsor vertebra.
3. Appendicular skeleton
(1) Shoulder girdle, sternum, and forelimb bones
(1) Shoulder girdle: semi-circular, symmetrical. Each side of the shoulder girdle includes dorsal and abdominal parts, with the upper scapula and scapula on the back, and the clavicle and olecranon on the abdomen.
Upper scapula: a flat bone located on the back of the shoulder. Its posterior margin is cartilaginous.
Scapula: attached to the upper scapula at one end and forming the dorsal wall of the shoulder socket at the other end.
Clavicle: located anteriorly on the ventral surface and is thin and rod-like.
Ulna: located slightly posterior to the clavicle, a thicker rod-shaped bone. Its outer end forms the shoulder socket together with the scapula, and its inner end is connected to the upper rostral bone.
Upper uvula: located between the right and left uvula and clavicle, 1 pair of elongated bone fragments, not yet fully ossified, converging in the midline of the abdomen, unable to move, called solid thoracic type.
Shoulder girdle (the right and left upper olecranon bones of toads are arc-shaped and overlap each other, and can be moved, called the arc-thoracic type).
② Sternum: located on the ventral midline of the thorax. In frogs, the sternum consists of a series of bones and is divided into two parts, bounded by the upper urosternum. Toads have only 1 block.
(iii) Forelimb bones: Bone blocks constituting the 5 parts of the forelimb such as the upper arm, forearm, wrist, palm and fingers.
Humerus: a long rod-shaped bone of the upper arm, rounded proximal end, embedded in the shoulder socket to form the shoulder joint; distal end and radial ulna of the forearm to form the elbow joint.
Radius-ulnar: a long bone of the forearm formed by the merger of the ulna and radius, with a longitudinal groove on each of the inner and outer surfaces of the diaphysis where the two bones meet, especially the distal portion is more pronounced.
Carpal bones: 6 small irregularly shaped bones located in the wrist, arranged in two rows of 3 bones each.
Metacarpals: 5 small bones in the metacarpals, the first metacarpal is extremely short and small, the rest of the metacarpals are elongated and of similar length.
Phalanges: 4 fingers of the forelimb, articulated at the distal ends of the second, third, fourth and fifth metacarpals respectively. The first and second fingers each have 2 phalanges, the third and fourth fingers each have 3 phalanges, and the third and fourth fingers each have 3 phalanges. The third and fourth fingers have 3 phalanges each.
(2) Girdle and hind limb bones
(1) Girdle: it is the support of the hind limb, which is composed of three pairs of bones, namely, ilium, sciatica and pubis, and the back of it is in the shape of "V", and each of the two outer surfaces of the three bones at the place of healing forms a concave fossa, which is called the acetabulum. The back of the girdle is connected to the tailbone in the middle.
Iliac bones: a pair of long bones, the anterior end is connected to the two transverse processes of the sacrum, and the posterior end is fused with the other two bones, forming the anterior wall and part of the dorsal wall of the acetabulum.
Sciatic bones: situated posterior to the ilium. The right and left sciatic bones merge to form the posterior and part of the dorsal wall of the acetabulum.
Pubic bone: situated on the ventral surface of the posterior part of the girdle, the right and left pubic bones are merged. The right and left pubic bones are fused together to form the abdominal wall of the acetabulum.
② hind limb bones: the bone blocks that constitute the 5 parts of the hind limb such as femur (thigh), tibia (calf), tarsus, metatarsus and toe.
Femur: a long bone of the femur, the proximal end of which is in the shape of a ball called the femoral head, embedded in the acetabulum constituting the hip joint, the distal end of the tibiofibular joint.
Tibiofibula: a long bone of the tibia, with a shallow longitudinal groove in the center of the internal and external surfaces of the backbone, indicating that this bone is formed by the merger of the tibial and fibular bones. Its proximal end forms the knee joint with the femur, and its distal end articulates with the tarsus.
Tarsal bones: 5 in 2 rows. Associated with the tibiofibula is a pair of short, rod-shaped bones, the lateral one being the fibular tarsus (heel bone) and the medial one called the tibial tarsus (talus), which are fused at the upper end and close to each other at the lower end. The other 3 are granular and line up in a horizontal row between the heel bone, talus and metatarsus.
Metatarsals: are the 5 long bones that link the tarsus and phalanges, the fourth being the longest. There is a small hooked spur on the medial side of the first metatarsal, also known as the pre-metatarsal.
Toes: five toes of the hind limb, the first and second toes have two phalanges, the third and fifth toes have three phalanges, and the fourth toe has four phalanges.
Muscular system
Use the double destruction of the medulla method to execute the live frog. Hold the frog in the left hand so that its back is upward. Press the front of its head with the index finger and its back with the thumb so that the head is bent forward. The right hand holds a dissecting needle from between the eyes along the midline to the posterior end, and when it touches a depression where the foramen magnum of the occipital bone is located, the needle is stabbed vertically into the foramen magnum of the occipital bone. Then the tip of the needle is stabbed forward into the cranial cavity, and the brain is destroyed by stirring in the cranial cavity. If the needle is really in the cranial cavity, you can feel the needle touching the skull. Then the needle was retreated to the occipital foramen, the tip of the needle was turned to the back and stabbed into the vertebral canal parallel to the spine, and the medulla oblongata was destroyed by rotating the needle as it was inserted until the hind limbs of the frog and the abdominal muscles were completely relaxed.
The executed frog was placed ventrally upward in a dissection tray and the limbs were spread. Holding forceps in the left hand, the skin slightly anterior to the cloaca between the bases of the hind legs on the ventral surface was clamped, and with scissors in the right hand, all cuts were made, from which the skin was cut forward along the ventral midline to the anterior end of the mandible. The skin of the forelimbs was then cut and peeled off at the shoulder girdle to either side; a circular incision was made in the femur and the skin peeled off to the foot.
Observe the major muscles of the jaw, abdominal wall, and limbs.
1. Superficial muscles of the mandible
(1) Submandibular muscle
A thin sheet of muscle located on the ventral surface of the mandible, forming the main part of the floor of the oral cavity. The muscle fibers run transversely between the two mandibles, with a tendinous division at its midline, dividing it into right and left halves.
(2) Sub-chin muscle
It is a small, slightly rhombic-shaped muscle located at the anterior angle of the mandible, with its anterior edge close to the mandibular symphysis, and the muscle fibers running transversely.
2. Major superficial muscles of the abdominal wall
(1) Rectus abdominis muscle
Located in the middle of the abdomen is a wide amplitude muscle, muscle fiber Xinwei longitudinal, starting from the pubic symphysis, stopping at the sternum. The muscle is divided into two halves by its central longitudinal connective tissue white line (abdominal white line), and each half is divided into several sections by four to five transverse tendons.
(2) Obliquus abdominis
A thin sheet of muscle located on either side of the rectus abdominis muscle, divided into two layers, inner and outer. The fibers of the external oblique muscle run diagonally from the anterior dorsal to the posterior aspect of the abdomen. The inner layer of the obliquus abdominis can be seen by gently scratching the obliquus abdominis, and the direction of the fibers of the obliquus abdominis is opposite to that of the obliquus abdominis.
(3) Pectoral muscle
It is located in front of the rectus abdominis muscle and is fan-shaped. It starts from the sternum and the tendon membrane of the lateral rectus abdominis muscle and ends at the humerus.
3. Brachial muscles of the forelimb
(1) Triceps brachii
Located on the back of the humerus, it is the largest muscle of the upper arm. There are three muscle heads at the starting point, respectively from the upper and inner surfaces of the proximal humerus, the posterior border of the scapula and the outer surface of the humerus, ending at the proximal end of the radial ulna. It is an important muscle for extending and rotating the forearm.
4. Muscles of the hind limb
(1) Thin femoral muscle
Located on the medial side of the thigh, it occupies almost half of the ventral surface of the thigh and allows the thigh to be turned backward and the calf to be extended and flexed.
(2) Stitchers' muscle
A long, narrow, band-like muscle located in the midline of the ventral surface of the thigh. The muscle fibers run obliquely, starting at the anterior edge of the ilium and pubic bone fusion and ending at the medial side of the proximal tibiofibular bone. When contracted, it can make the calf abducted and the end of the thigh adducted.
(3) Triceps femoris
It is the largest muscle located on the lateral side of the thigh and can be visualized by turning the specimen from the ventral to the dorsal surface. There are three muscle heads at the starting point, respectively from the central ventral surface of the ilium, the back, and the anterior ventral surface of the acetabulum, and its end with a common tendon across the knee joint stops below the proximal end of the tibiofibula. When contracted, it enables the calf to be extended and abducted anteriorly.
(4) Biceps femoris
A narrow muscle, between the semimembranosus and triceps femoris and mostly covered by them. It originates from the back of the hip bone just above the acetabulum, and the terminal tendon is divided into two parts, attaching to the distal end of the femur and the proximal end of the tibia respectively. When contracted, it can make the calf flex and lift the thigh.
(5) Semimembranosus
It is a broad muscle located behind the biceps, starting from the dorsal edge of the sciatic union and ending at the proximal end of the tibia. When contracted, it enables the thigh to be flexed forward or backward and the calf to be flexed or extended.
(6) Gastrocnemius
It is the largest muscle at the back of the calf, and is commonly used as a laboratory material in physiology. There are two muscle heads of different sizes at the starting point, the larger one starts from the flexion surface of the distal femur, the smaller one starts near the end of the triceps femoris muscle, and its end crosses the ventral surface of the tarsus with an Achilles tendon and stops at the metatarsal region. The contraction causes flexion of the calf and extension of the foot.
(7) Tibialis anterior muscle
It is located in front of the tibiofibula. It originates from the distal end of the femur and attaches to the heel and talus with two tendons at its end. It straightens the calf when contracted.
(8) Peroneus brevis
It is located on the lateral side of the tibiofibula, between the gastrocnemius muscle and the tibialis anterior muscle. It starts at the distal end of the femur and ends at the heel bone. It extends the calf when contracted.
(9) Posterior tibialis muscle
It is located in front of the medial gastrocnemius muscle. It begins at the inner edge of the tibiofibular bone and ends at the talus. It extends and bends the foot when contracted.
(10) Tibial extensor
Located between the tibialis anterior and tibialis posterior muscles. It starts at the distal end of the femur and ends at the tibiofibula and can straighten the calf when contracted.
V. Demonstration
Teachers use electrical stimulators to stimulate the pectoral muscles, triceps brachii, triceps femoris and biceps femoris, gastrocnemius and tibialis anterior muscles of frogs (or toads) that have just been executed and skinned, demonstrating the contraction and diastole of the muscles and helping students to understand the relationship between the muscles, bones and joints, as well as the synergism of the muscle groups and the physiological activities of antagonism.
VI. Oropharyngeal Cavity
A common passageway for the digestive and respiratory systems.
1. tongue
Left hand holding forceps to pull down the frog's lower jaw, can be seen at the bottom of the 1:1 cavity in the center of a soft muscular tongue, the base of which was born in the lower jaw anterior medial, the tip of the tongue backward to the pharynx. The right hand with forceps gently pull the tongue from the oral cavity to the outside out to flatten, you can see the frog's tongue tip forked (toad tongue tip bluntly rounded, not forked), with a finger touching the tongue surface has a viscous slippery feeling. How to catch food with frog's tongue? Hold the scissors in the right hand and cut the left and right corners of the mouth to the bottom of the tympanic membrane, so that all the oropharyngeal cavity is exposed. 2.
2. Inner nostril
1 pair of oval holes, located at the top wall of the cavity near the anastomosis. A bristle is taken through the external nostril, and the bristle is seen to pass out through the internal nostril. What is the function of the internal nostrils?
3. teeth
Along the edge of the upper jaw there is a row of fine, pointed teeth with the tips pointing backwards, the maxillary teeth (toads have no teeth); between one pair of internal nostrils there are two clusters of fine teeth, the plow teeth (toads have no teeth). What is the purpose of the teeth?
4. Eustachian tube orifices
A pair of large foramina located on either side of the parietal wall of the cavity, near the angle of the jaw. A forceps is gently inserted through these holes to reach the tympanic membrane.
5. Acoustic sac orifices
At the bottom of the male frog's mouth, at the corners of both sides of the mouth, slightly in front of the hole of the eustachian tube, there is a pair of small holes, i.e., the acoustic sac holes (male frogs are not tied here).
6. Laryngeal Portal
It is a rounded protuberance with longitudinal fissures on the ventral surface behind the tip of the tongue. It is supported by a pair of semicircular arytenoid cartilages, and the longitudinal fissure between the two cartilages is the laryngeal valve, which is the opening of the laryngotracheal chamber in the pharynx.
7. Esophageal orifice
Dorsal to the laryngeal portal, a daisy fold-like opening at the base of the pharynx.
(1) After observing the oropharyngeal cavity, cut the skin.
(2) The posterior end of the rectus abdominis muscle between the bases of the two hind limbs is lifted with forceps, and the abdominal wall is cut with scissors along the abdominal midline slightly to the left of the midline from back to front (so as not to damage the abdominal vein located in the midline), and when the cut reaches the sabre sternum, the olecranon and scapulae are cut with diagonal scissors along the left and right sides of the sabre sternum.
(3) Gently lift the saber sternum with forceps, carefully peel off the connective tissue between the sternum and the pericardium (taking care not to damage the pericardium), and finally cut off the sternum and chest muscles.
(4) Strip the abdominal vein at the midline of the abdominal wall from the abdominal wall; then turn the abdominal wall to the sides and fix it on a wax plate with a large headpin.
(5) At this point the heart, located at
(1) Draw a sketch of the circulatory system of a frog (or toad) with the names of the various organs.
(2) Based on anatomical observations, draw a structural diagram of the cloacal system of the frog (or toad) with the names of the organs.
2. Reflection Questions
(1) What aspects of amphibians are characteristic of terrestrial vertebrates?
3. Questions and Answers
(1) Compare the similarities and differences in the structure of the digestive, respiratory, and cloacal systems of a fr