Overview
This lecture reviews the external and internal anatomy of the common Norwegian rat (Rattus norvegicus), covering major body systems, anatomical terms, and organ identification.
External Anatomy
- The external ear (pinna) directs sound into the ear canal (external auditory meatus).
- Eyes have upper and lower eyelids and a nictitating membrane for protection.
- Whiskers (vibrissae) serve a sensory function.
- External nares are the nostrils.
- Females have mammary papillae (nipples), typically six per side.
- Female rats have separate urethral and vaginal orifices; males have one urogenital opening.
- Male testes are in the scrotum; penis is often hidden within a fold of skin.
Anatomical Terminology
- Cranial: toward the head; Caudal: toward the tail.
- Dorsal: back side; Ventral: belly side.
- Lateral: toward the side; Medial: toward the midline.
- Proximal: closer to point of attachment; Distal: farther from point of attachment.
Skeletal System
- Skull bones include parietal, frontal, zygomatic arch, maxilla (upper jaw), and mandible (lower jaw).
- Incisors grow continuously and are worn down by gnawing.
- Vertebrae are categorized as cervical (neck: atlas & axis), thoracic (rib area), lumbar, sacrum, and caudal (tail).
- Main limb bones: scapula (shoulder), clavicle (collarbone), humerus, radius, ulna, femur, patella, tibia, fibula.
- Hands and feet have carpals, metacarpals, tarsals, and phalanges.
- Pelvic bones: ilium, pubis, ischium.
Muscular System
- Each muscle has an origin (stationary attachment) and insertion (moves during contraction).
- Main muscles: gastrocnemius (calf), tibialis anterior (front of tibia), external oblique and rectus abdominis (abdomen support), latissimus dorsi (pulls arm caudally).
- Sternomastoideus (rotates head), sterno-hyoid (supports tongue base), spinal deltoideus (moves scapula), gluteus superficialis (moves thigh outward).
- Biceps femoris (flexes lower leg), triceps and biceps brachii (forearm movement).
- Masseter and temporalis (jaw movement), acromiotrapezius (scapula movement), intercostals (aid breathing).
Internal Anatomy
- Hard and soft palate make up the roof of the mouth; tongue and incisors visible.
- Thymus sits above the four-chambered heart; lungs flank the heart.
- Diaphragm separates thoracic and abdominal cavities.
- Trachea (windpipe) is in front of the esophagus; branches into bronchi at lungs.
- Liver (largest abdominal organ); rats lack a gallbladder.
- Stomach is J-shaped; pancreas and spleen located nearby.
- Small intestine subdivided into duodenum, jejunum, ileum; large intestine begins at cecum.
- Female reproductive system: ovaries, oviducts (Fallopian tubes), uterine horns, uterus.
- Mesentery holds intestines in place.
- Kidneys are retroperitoneal (behind abdominal lining); adrenal glands sit atop kidneys.
- Main blood vessels: abdominal aorta (artery), inferior vena cava (vein).
- Ureters connect kidneys to urinary bladder.
- Male reproductive system: testes (in scrotum), epididymis, vas deferens, seminal vesicles, penis.
Key Terms & Definitions
- Pinna — External ear flap directing sound into the ear canal.
- Vibrissae — Long, stiff whiskers with sensory function.
- Nictitating membrane — Protective inner layer in eye corner.
- Mammary papillae — Nipples found in female mammals.
- Origin — Muscle’s stationary attachment.
- Insertion — Muscle’s moving attachment during contraction.
- Retroperitoneal — Located behind the abdominal cavity lining (e.g., kidneys).
- Mesentery — Thin tissue holding organs, especially intestines, in place.
Action Items / Next Steps
- Practice identifying all major organs and structures on a rat specimen or diagram.
- Review and memorize key anatomical terms and locations.
- Prepare for dissection by reading the next chapter on rat organ systems.