The single or double lobed thymus is found craniolateral to the thyroid gland, closely associated with the vagus. It does
not involute when the animal matures as it does in higher vertebrates. Just caudoventral to the thymus is the thyroid. It
is a spherical reddish-pink structure cranioventral to the heart and ventral to the trachea.
Reptiles have one or two pairs of parathyroid glands which can be found either cranial or caudal to the thyroid. In turtles
the glands may be found imbedded in the thymus. These glands are difficult to find and are often obscured in the adipose tissue.
All reptiles have a pair of adrenal glands. They are found closely associated with the gonads and urogenital structures of
the lizard and snake and with the kidneys in the turtle. The adrenals are pinkish filiform structures found medial to the
gonads. Unlike mammals, the medullary and cortical tissue is indistinguishable, but nonetheless still produces the appropriate
For the most part the mouth does little more than catch the food. Very little mastication, if any, occurs. The saliva that
is produced has little digestive significance, its role being mostly lubricatory. The esophagus has a special adaptation of
several longitudinal folds which allow for great distensibility of the gut to accommodate large food items. The esophagus
is dorsal to the trachea and extends from the pharynx to the stomach.
The stomach of the snake is fusiform, and in the lizard and turtle its shape grossly resembles the mammalian stomach. The
stomach is rather short in the snake. Its junction with the esophagus is clearly noted at a site approximately equal to three-fourths
the length of the liver. The stomach ends in a stricture, the pylorus, at the pyloroduodenal junction.
The small intestine may be either straight or have short transverse loops. The small intestine in the lizard and turtle has
many loops and convolutions much the same as in the mammal. The small intestine terminates at the ileocolic junction. A cecum
is present in some snake species. A cecum is present in both the lizard and the turtle.
The large intestine terminates at the cloaca. It is a short, straight tube. As in the bird, the reptilian cloaca has three
chambers. The feces are discharged into the anterior chamber called the coprodeum. The next, or middle chamber, called the
urodeum, receives the urogenital ducts. The posterior proctodeum acts as a general collecting area for digestive and excretory
wastes. The male intromittent organs open into this compartment, and both the male and the female have scent glands which
also open here.
The reptile has a metanephric kidney. It is situated in the posterior part of the body positioned adjacent to the body wall,
with the right kidney anterior to the left. They are brown in color and consist of twenty-five to thirty lobes. Since the
snake lacks a bladder the ureters enter directly into the urodeum. The lizard and turtle the ureters enter the bladder, which
then empties directly into the urodeum.
Both the male and female gonads are found in the posterior half of the body. They are medial to the kidneys and in the snake,
the right is cranial to the left. The testes are off-white to yellow, and the ovaries are a yellowish pink.