The muzzle is of varying lengths, depending on the breed. Whiskers, present on the muzzle, are of some sensory use. Dogs also have a 'stop' on their heads, which is the point where the muzzle ends and the forehead begins. It is quite prominent in some breeds, but barely visible in others. Dogs have dichromatic vision, and they cannot see the colors green and red. They have a very sharp sense of hearing and smell. They can hear sounds that are undetectable to the human ear. As compared to the 2 to 3 million scent glands that humans possess, dogs have between 200 to 300 million. The tail set is from where the tail begins. Some dogs have high-set tails, while some have low-set tails. Like the elbow on the foreleg, there is a hock present on the hind leg. It is a joint which juts in an outward direction.
Trachea - The trachea is actually a tube that transports inhaled air to the lungs.
Esophagus - It is the tube that connects the throat to the stomach, thus, aiding in transporting food for digestion.
Larynx - It houses the dog's vocal cords.
Heart - As in humans, this organ performs the function of pumping blood throughout the body.
Liver - It performs the function of producing bile and aiding in the process of digestion.
Kidney - The kidney filters the blood and purifies it of all the toxins that are harmful for the dog.
Stomach - The stomach is located between the esophagus and the intestine. It is the organ which breaks down the food and mixes it with the digestive juices.
Spleen - It produces red blood cells, filters and removes old cells, stores the red cells, and forms an integral part of the immune system.
Bladder - It stores the urine until it is eliminated.
Rectum - It is an organ located at the end of the large intestine, which expels stool.
The first stage is called proestrus, which is the beginning of the heat cycle. During this stage, the dog's vulva appears swollen, and there is a bloody discharge. This stage can last between 5 to 9 days. The second stage is the estrus, wherein the reproduction process takes place.
A female dog's reproductive system involves the uterus, the cervix, the oviducts, the ovaries, and the vagina. The ovaries are the organs that are responsible for the production of unfertilized eggs in the female. They also play a very important role in sustaining the pregnancy. The unfertilized eggs then pass to the oviduct. The oviducts are thin tubes in which the process of fertilization of the eggs by the sperm takes place. The fertilized eggs, known as zygotes, are then transported to the uterus, where their placentas stick to its walls. The zygotes mature, become embryos, and then become fetuses. The uterus is also made up of the three parts: the right uterine horn, the left uterine horn, and the main uterine body. The uterine horns are the place where the Fallopian tubes and the uterus attach.
The third stage in the female's estrous cycle is the diestrus stage, where the female is either pregnant or experiences pseudo-pregnancy. If the dog is pregnant, then she goes into gestation (the time between conception and birth). The gestation period of dogs is between 60 to 65 days, after which the pups are born. However, as the hormonal changes during the diestrus period are the same whether the dog is pregnant or not, she can also have a pseudo-pregnancy, wherein she goes through all the physical changes related to a pregnancy, like enlarged mammary glands, milk production, weight gain, and nesting tendencies.
The sperm originates, or is prepared, in the testicles. When the dog ejaculates, the sperm goes through the vas deferens, into the prostate gland, where it combines with the prostatic fluid. From there, it goes to the urethra, and is then expelled from the dog's body through the penis. The penis contains two sections: the bulbous glandis or glans penis, and the os penis. The os penis is actually a bone inside the penis, which helps the dog achieve successful intercourse, whereas the glans penis helps the dog sustain the intercourse. It does so by filling up with blood and increasing in size, thus preventing the penis from exiting the vulva. This raises the chances of a successful fertilization.
One extremely important part of a dog's skeletal anatomy is the skull. It is a long bone structure that encases the brain, and contains a cavity called the orbit, where the eye is located. It is elongated and extends to the end of the muzzle. Next comes the vertebra or spine. It is divided into five parts: the cervical, dorsal, lumbar, sacrum, and caudal vertebrae. It has 30 vertebrae, of which 7 are cervical, 13 are dorsal, 7 are lumbar, and 3 are sacral. The cervical vertebrae are those of the neck, which follow the skull. The dorsal, lumbar, and sacrum vertebrae follow, respectively. The caudal vertebrae are the bones of the tail. The rib cage is located under the vertebra.
The lower side of the muzzle is called the lower maxillary. At the base of the cervical vertebrae and just before the rib cage is the shoulder bone, which is called the scapula. This further extends to the humerus, which is the upper half of the foreleg. It further extends down to a pair of bones, known as the ulna and the radius, which form a part of the lower half. Then comes the wrist bone, called the carpus, the paw bone which joins the wrist and the toes, known as metacarpus, and then the toe bone, known as the phalange. The rear legs of the dog begin with the femur bone, which extends to a pair of bones known as the tibia and the fibula. These further extend to the heel bone, known as tarsus, the paw bone, known as metatarsus, and the toe bone, phalange.