Kingdom Animalia
Subphylum Vertebrata
(Campbell 6th Ed. 682-716; 7th Ed. 678-708)
As an introduction to the vertebrates, you will examine the body systems of the rat and in a later laboratory, study selected systems of the frog for comparison.
In studying the vertebrates, it is important to realize that many aspects of Zoology depend on anatomical relationships. However, the knowledge of structure alone has only limited meaning if it is not interpreted in terms of function. Although the emphasis may at times be placed on observation of anatomical structures, it is vital that students consider the function of these structures.
Organization of Laboratory Exercises
During the remainder of the laboratory you will examine the external anatomy of the rat and study the skeletal systems of fish, frog, bird and rat. Additional laboratory work on the Chordates is divided into the next 5 laboratory sessions:
In order to understand the dissection instructions and locate structures you MUST be familiar with the following Descriptive Terms:
| Anterior | pertaining to the front or head end |
| Caudal | concerned with the tail region of the animal |
| Cephalic | concerned with the head region |
| Distal | pertaining to the farthest point of attachment |
| Dorsal | referring to the back or uppermost side |
| External and Internal |
outer and inner |
| Frontal Section | a longitudinal, horizontal section which parallels dorsal and ventral surfaces |
| Lateral | at the side of the body or situated to either side of the midline |
| Longitudinal Axis | a lengthwise axis from head to tail end of an animal |
| Medial | at the midline of the body |
| Median Plane | a vertical longitudinal plane that extends from the ventral to dorsal surfaces (Produces a sagittal section). |
| Peripheral | region away from centre |
| Posterior | pertaining to the tail or hind end |
| Proximal | pertaining to the region near the body |
| Sagittal Section | a longitudinal section through the median vertical plane |
| Superficial | region near the surface |
| Transverse Section | a section made at right angles to the sagittal and frontal section |
| Ventral | referring to the underside. The opposite to dorsal. |
NOTE: All position terms such as "anterior", "right", etc., are with reference to the specimen's anterior end, right side, etc.
Examine an image of the rat showing a few of these terms
The Rat
(A Representative Chordate and Mammal)
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Two common species of the genus Rattus, the Black Rat (R. rattus) and the Brown or Navy Rat (R. norvegicus), are similar in size and appearance, and therefore, difficult to tell apart by superficial examination. This problem is even greater in many laboratory specimens, since mutant white albinos from either species are commonly used. As is often the case, however, closer examination of one or more characteristic external features, even in albinos, provides sufficient information to permit species identification. In Rattus spp. the ratio of tail length to body length differs between species. In R. rattus, the tail length is typically greater than the body length; while in R. norvegicus, the tail length is typically less than the body length.
A typical chordate has a number of distinctive characteristics, both external and internal. In this portion of the laboratory, we shall be concerned with the former.
The chordates are bilaterally symmetrical, show a high degree of cephalization with a close association between the brain and special senses, have a definite trunk region with associated appendages, have an anterior mouth and a post-anal tail. Most of these characteristics reflect the active mode of life pursued by the chordates, in which locomotion is typically directed anteriorly, parallel to the longitudinal body axis. However, modifications to this plan are numerous and in many cases there is a strong link between the degree of modification and the animal's environment.
As a typical mammal, the rat posses two unique external characteristics that distinguish mammals from all other vertebrates:
The rat, like many other mammals possesses special stiff sensory hairs, the vibrissae, on the sides of the face. Click here to examine the vibrissae of Rattus spp.
Mammary glands are present in both sexes, but may be difficult to locate on the male and immature specimens. Typically three pairs of teats will be found on the ventral thoracic region, and an additional three pair posteriorly, on the ventral abdominal surface. The limbs of the rat are pentadactyl and tripartite; the hind limbs larger than the fore limbs. Note the terminal claws. The rat's gate, or mode of locomotion is called digitigrade, because the animal walks only on the digits of the foot, the remainder being held off the substrate. (In contrast, except for minor areas such as the instep, the entire foot of the human is placed on the substrate during walking, hence the gait is called plantigrade). Note the scales on the tail.
Examine
the female rat externally
Examine
the male rat externally
Before examining the skeletal muscles of the rat, carefully examine the skeletons of the following:
Pay particular attention to the shape of the cranium (head), the vertebral column, pectoral and pelvic girdle , and the fore and hind limbs. Observe closely the similarities in the skeletal structures between the four classes, Pisces (fish), Amphibia (frog), Aves (bird) and Mammalia (rat). List some similarities. Also note some differences in the shape of the pectoral (anterior) and pelvic (posterior) girdles and position of limbs relative to the girdles. You should be able to identify the bones of the fore limb ( humerus, ulna and radius) and the bones of the hind limb (femur, tibia and fibula). Differentiate between cervical (neck region), thoracic (rib region) and lumbar (abdominal region) vertebrae.
Many people are not aware that bone is a living tissue. Bone contains living cells and has a nervous supply along with a vascular supply. Bone can be added to or depleted. In fact bone tends to decalcify with age and become brittle. This is especially true in the human female. Diet and exercise will help to counteract this process. Bone is a tissue in which the extracellular component is highly calcified. It is close to cast iron in tensil strength but is less than one third the weight.
Examine
the bone cross section x10
Examine
the bone cross section x40
On viewing you will notice a number of relatively large dark ovals or circles with a concentric arrangement of tissue around the outside. The central dark oval or circle is known as a Haversian canal. The Haversian canal contains elements of the vascular system to provide nutrients to the bone and remove waste materials from the bone. The concentric layers around the canals are called lamellae. Uniformly spaced along the lamellae are small cavities called lacunae. Each lacuna appears as a dark oval in these preparations but in living bone each contains one bone cell known as an osteocyte. Osteocytes are responsible for secreting the extracellular matrix which makes up most of the mass of the tissue. Radiating from the lacunae are very fine passages called canaliculi. In these preparations the canaliculi appear a dark thread-like lines extending out from the lacunae. There are connections between the haversian canals, the lacunae and the canaliculi. Bone is thus not solid but filled with a fine interconnecting system of canals. One haversian canal with its surrounding lamellae makes up a cylindrical haversian system.
Make a sketch of bone tissue labelling the various parts.
