The Arteries 325 



though the essential relation of this to the disease is unknown, 

 nor is there any explanation why the recurrent character of the 

 nerve should cause disease in the horse and not in other animals. 



Fig. 54. Ectopia Cordis ; Schistocormus Fissisthrnalis. 

 After Hering. 



It should be noted here also that the heart sometimes becomes 

 arrested in its movement backward and remains in the cervical 

 or pharyngeal region. It thus occurs, especially in bovidae, 

 that the young may be born with the heart just beneath the 

 pharynx or at any point between this and the first rib, as shown 

 in Figs. 52 and 53, thus graphically reminding one of the normal 

 siifting of the location of the heart from its first position along 

 the floor of the pharynx, in the embryo, toward the posterior 

 portion of the body, to become lodged within the chest cavity. 



In other cases, the aberration in the location of the heart 

 may occur in connection with a fissure of the sternum, through 

 which the heart becomes herniated, as in Pig. 54. 



The fifth aortic arch gives off a branch, before joining the 

 aorta, to go to the lungs and constitute the pulmonary, artery. 

 In the right vessel, the arch disappears between the pulmonary 

 artery and the aorta, while, in the left, it continues up to the 

 close of fetal life, as the ductus arteriosus, which, up to the time 

 of birth, maintains the indirect communication between the right 

 ventricle and the posterior aorta, and persists throughout life as 

 a fibrous cord, the ligamentum arteriosum. 



