284 Dynamic Theory. 



with a rather rare anomaly of the great veins going to the heart from 

 the upper part of the body. The usual arrangement in man on each 

 side, is for the great vein of one arm and the corresponding side of the 

 head to unite and form a single trunk ( bracliio-ceplialic ), so we have 

 two large venous trunks, one on each side. These two trunks then join to 



FIG. lie. 

 FIG. 116. E. Normal Arrangement of the Vena Cava and branches in the Human 



H. Right Auricle of the Heart. vc. Vena Cava. 



ji;'. Jugular veins from the head. ss. Subclavian veins from the arms. 



vcr. Remnant of the Foeta,] left vena cava. 



F. Abnormal arrangement in which the foetal left vena cava, vc, persists through life. 



form a single large vessel, called the superior vena cava, which empties 

 its blood into the right side of the heart. (See Fig. 116 E. ) It oc- 

 casionally happens that the great venous trunks formed by the veins of 

 the arm and head of each side do not unite to form the superior vena 

 cava, but each continues its downward course and opens separately into 

 the heart. (See Fig. 116 F. ) On studying the development of the 

 blood-vessels, we find that in early foetal life this condition of affairs 

 exists, but after a time a transverse branch forms between the two 

 trunks. This branch gradually enlarges, while the left trunk shrivels up 

 and at birth is only represented by a fibrous cord. This anomaly of the 

 veins we find then, is a persistence of a usually transient foetal con- 

 dition in man, and also that in all birds, and many of the lower mam- 

 mals, it is the permanent condition." 



' ' In man the skin muscles are very feebly developed compared with 

 those seen in many of the lower animals. The only remnants of these 

 in man are the muscle which wrinkles the forehead (occipito-frontalis)^ 

 the muscle immediately under the skin covering the side of the neck 

 (platysma myoides}, and the palmar is l>r< T/.S, a little bundle of muscu- 

 lar fibres in the palm of the hand." (There is one other piece.) "Not 

 unfrequently remnants appear abnormally in other situations, as over 

 the breast, in the arm-pit, on the back, &c. The skin muscles are well 



