234 ESSENTIALS OF ZOOLOGY 



Cardiac Anomalies 



Transposition of the heart to the right side of the midline of the 

 body is known as dextrocardia and occurs rarely. It is usually asso- 

 ciated with displacement of other visceral organs. 



Due to faulty development, an incomplete interventricular septum 

 is occasionally found in the four-chambered hearts. The failure of 

 complete development of the septum between the auricles to close 

 the foramen ovale is a more common anomaly. It has been reported 

 that this occurs in some degree in one case in four for the human 

 being. Actual mixing of auricular blood sufficient to interfere with 

 normal function is much less common, however, because of the over- 

 lapping of the membranous walls which are pressed together by 

 the pressure of contraction. In a small number of human cases the 

 aerated blood and unaerated blood from the two auricles do mix 

 and produce a purplish colored blood which in turn affects the color 

 of the skin. Such a case is known as a ''blue hahy'* and often 

 leads to early death. 



Abnormalities of Brain and Sense Organs 



Encephalocoele is due to the protrusion of a sac of the meninges 

 and part of the brain through a defect in the roof of the cranium. 

 An abnormally large brain, which is usually associated with the 

 distention of the cranium by superabundance of cerebral fluid, is 

 known as hydrocephalus, or the size may be macro cephalus. The 

 opposite extreme in which the head and brain are abnormally small 

 due to failure of development is known as microcephalus. 



There are cases of cleft nose in which the nostrils are in inde- 

 pendent projections. This condition is usually associated with hare- 

 lip and cleft palate. With regard to the eyes there are several 

 possible abnormalities. Cyclopia is a condition in which there is 

 a single median eye like that of the Cyclops instead of the usual 

 paired arrangement. In such cases the nose is usually at the base 

 of the forehead, above the eye, and cylindrical in shape. Failure 

 of complete development of the iris or chorioid, thus leaving a gap 

 or open sector in the margin of the pupil, is known as coloboma. 



