Biology of magical creatures
Abstract
Centauroids are common species in magical ecosystems, representing a half-human, half-ungulate composite animal. Although they seem perfectly logical in their appearance, their internal anatomy is far more complicated than expected. Although they look like having the upper part of a human and the whole body without the neck and the head of a horse (or another ungulate), this does not mean they also possess doubled sets of internal organs. In this paper, we made an overview of the common anatomical features of centauroids with emphasis on the main specializations.
Diversity of centauroids
Centauroids are magical creatures, resulting from the unlikely mixing of the bodies of two species – a humanoid and an ungulate. The exact mechanism might differ between different centauroids and is not the subject of the current paper. However, a short overview of the known species is presented, as the anatomical features of most of them seem to be common.
Table 1. Diversity of centauroids in different magic worlds.
Centauroids are known and widely distributed in many magical-rich ecosystems. They represent a sentient species, often living in tribal societies and are esteemed fierce fighters. Although the archetype of a centaur consists of the body of a horse with the torso, head and hands of a human, attached in place of the horse head, there are many variations of this image, encompassing the range of centauroid species. They are subdivided based on 1) the humanoid species; 2) the ungulate species and 3) the presence of horns. A few examples are given below in table 1. Irrespectively of their origin and appearance, all centauroids face the same anatomical challenges, regarding their internal anatomy.
Skeletal system
A comparatively weak point in the centauroid skeleton is the junction between the humanoid and ungulate vertebral column. At this point, the vertebral column makes a nearly 90-degree angle, which significantly increases the possibility of breaking the spinal cord. For this risk to be diminished and to sustain greater physical tension, peculiar vertebrae evolved – vertebrae transeuntem, which is derived from the sacrum of the humanoid body and is further stabilized by the modified iliums. The vertebrae transeuntem is a composite bone (made of 5 sacral vertebrae), allowing the smooth curve of the spinal cord from the humanoid into the ungulate body. The humanoid coccyx is missing, as well as the cervical vertebra of the ungulate.
Nervous system
The main modifications of the single brain are related to the need for better coordination of both bodies and include enlargement of the motor cortex, which also results in enlargement of the skull.
Gastrointestinal tract and related organs
The gastrointestinal tract of centauroids is roughly equally distributed between the humanoid and ungulate bodies. A considerably long esophagus and a first stomach are situated in the humanoid section. Next, a short connection moves into the second stomach in the ungulate bodies. Small and large intestines are entirely situated in the ungulate section. Because most of the digestion and absorption occur in the ungulate body, the liver is also there to ensure efficient secretion of pancreatin and the overall digestive metabolism. Meanwhile, the lack of most of the larger internal organs in the humanoid body allows for larger space to be available for the enlarged lungs. Accordingly, the kidneys and the rest of the urinary tract are also situated in the ungulate body.
Respiratory and cardiovascular systems
The major physiological challenge in front of centauroids is the need for efficient blood flow and oxygen supply to both bodies. This is especially important not only because the lungs and the heart must ensure proper oxygenation of two separate bodies with a combined weight of over 500 kg, but also because this capacity must sustain fast pace running. Starting with the lung capacity, the vital capacity of human lungs is approximately 3 to 5 liters, while the vital capacity of the horse lungs is 10 fold bigger – up to 45 liters. Roughly speaking, the lungs of a centauroid must possess a vital capacity of 50 liters, while fitting in the chest of the human body. Not an easy task indeed, but what is helping is that the chest of a centauroid is usually much broader than the one of a regular human. The diaphragm is also situated lower than in humans, reducing the volume of the abdominal cavity, occupied only by the stomach and allows the increase of the lungs volume.
Figure 1. Rough distribution of the major organs of the respiratory (blue), cardio-vascular (red) and digestive (green and brown) systems between the human and equine body of a centauroid. 1 – enlarged lungs; 2 – first heart; 3 – second heart; 4 – liver; 5 – first stomach; 6 – second stomach; 7 – small intestines; 8 – large intestines.
Similarly, the combined stroke volume (volume of blood, pumped by the left ventricle) of the heart must be somewhere close to 1000 mL (less than 100 mL for the human body and over 900 mL for the horse). Even a hypertrophic heart in the human body would not be able to ensure such a volume. In addition, the blood flow will be severely hampered by the distance to the heart.
To face this challenge, the cardiovascular system of centauroids consists of a unique two-heart system. First, the oxygen-enriched blood from the lungs enters the left atrium of the humanoid heart through the pulmonary vein. Next, the blood is pumped from the left ventricle in the aorta, which shortly after this branches into the smaller primary aorta and the larger secondary aorta. The primary aorta and its further branches supply blood to the humanoid body, while the secondary aorta supplies blood to the left atrium of the ungulate heart. Its left ventricle pumped blood through the aorta equinus to supply blood for the horse’s body. Then, the carbon dioxide enriched blood reaches the right atrium and ventricle of the horse heart, is pumped back to the humanoid body through vena cavae equinus, which joins the vena cavae hominum and goes into the right atrium and ventricle of the humanoid heart. Finally, the right ventricle pumps the blood through the pulmonary arteries to the lungs to release carbon dioxide and be enriched in oxygen again.
As the horse heart is much bigger than the humanoid one, its heart rate is approximately two times lower (120 compared to over 250 beats per minute). The higher heart rate of the humanoid heart is supposed to provide enough oxygen-enriched blood to the ungulate heart.
References
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