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Facial and Masticatory Muscles |
Photos and text by Yu Jin Kim and Ana Panduro Part I Our specimen of Rattus norvegicus is female. Part II Kidneys are responsible for filtering toxins, mineral salts, and ingested water. The two reddish-brown organs are located in the dorsal side of the abdomen, one on each side medial to the spinal column. As in most mammals, the right kidney is slightly anterior to the left kidney, by about half a centimeter in the rat. The kidneys, shaped like beans, have a concave lateral side called the hilus, which is where the renal artery, renal vein, and ureter enter or leave. The left ureter attaches to the urinary bladder, which is a small, pear shaped organ, located ventral to the uterus, on the left side and the right ureter attaches to the bladder on the right side. Because the right kidney is located more anterior than the left, the right ureter is slightly longer [1]. Dissection Notes: The kidneys are surrounded by fat, except on the dorsal and ventral sides. The smaller adrenal glands, located anterior to each kidney, are completely embedded in fat. This lab involved little dissecting because we had already exposed the urogenital system in the digestion lab. Our main task was to remove the thick layers of fat found in the dorsal region of the abdominal cavity with tweezers in order to make the surrounding viscera more visible. In addition, we made a coronal incision on the anterior plane of the kidney in order to observe the cortex, medulla, and pelvis of the kidney. Because our specimen is injected with latex, the veins are visibly large, but the renal pelvis is undistinguishable from the medulla. Part IIIRattus norvegicus has one vagina and two uteri. Each uterus has its own distinct opening into the vagina and its own uterine horn [3]. The left uterine horn belongs to the left uterus and the right uterine horn belongs to the right uterus. In our specimen, each horn is about 5 cm long and borders the lateral walls of the posterior abdominal cavity, extending laterally from the uterus to the psoas major of its respective side. The uterine horns enclose a linear series of several hard, oval-shaped lumps. These lumps indicate that our specimen is pregnant because each lump contains an embryo inside. Our specimen has11 such lumps, indicating a litter size of 11. The litter size of Rattus norvegicus can range from 2 to 22, but 7-8 is the average [4]. Dissection Notes: With a scalpel, we cut open one of the lumps of the right uterine horn. However, we were unable to see any of the embryos. This means that all the fetuses are still in the early stages of development. The uteri were ventral to the rectum and dorsal to the bladder. Consequently, the vagina was ventral to the anus and dorsal to the urethral opening. However, the beaver, which is in the order Rodentia along with the rat, had a more derived arrangement of having a common cloaca in which the urethra and anus open into [2]. We were unable to find the clitoris of the rat, which is embedded in the vagina. Unlike female rabbits, which have a very large and protruding glans, the glans of our specimen was not even noticeable. References: 1. Hebel, Rudolf and Melvin W. Anatomy and Embryology of the Laboratory Rat. Stromberg. 1986. BioMed Verlag, Germany. 2. Living Kingdoms. Castor fiber. Retrieved on April 25, 2004 at Castor_fiber/Castor_fiber.html#Newly_hatched 3. Greene, Eunice C. 1935. Anatomy of the Rat. American Philosophical Society, Philadelphia. pp 92. 4. Living Kingdoms. Rattus norvegicus. Retrieved on April 26, 2004 at Rattus_norvegicus/Rattus_norvegicus.html#Parental
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Artwork: Weil, from Stubbs' 1776
"Anatomy of the Horse."
Background free from Eos Development, with
slight color modification.
