AETEEIES 



221 



artery with the aorta. After birth this is obliterated and forms the ligamentum 

 arteriosum. 



The inferior laryngeal nerves at an early stage reach their destination by passing 

 behind the pulmonary arches. When the heart is displaced backwards and the 

 systemic and pulmonary arches are carried with it, the points of origin of the nerves 

 from the vagus trunks are necessarily also drawn backwards, and they assume their 

 recurrent course. On the left side the primitive relationship to the pulmonary arch 

 is maintained i.e. the nerve loops round the obliterated ductus arteriosus ; but 

 on the right side, on account of the disappearance of this part of the arch, it comes 



post, cerebral a. 

 I 



ant. cerebral a. 



supra-orbital br. 

 of stapedial a. 



II. div.Vth n. 

 infra-orbital a. 



stapedial a. 



III. div. Vtt n 

 inf. dental a. 



int. carotid a. 



aortic arch 



pulmonary 

 arch 



pulmonary artery 



dorsal aorta 



FIG. 277. DIAGRAM TO ILLUSTRATE THE FATE OF THE AORTIC ARCHES AND THE ORIGIN OF THE 



MAIN BRANCHES OF THE CAROTID SYSTEM OF ARTERIES. (Founded On Tatldler.) 



to loop round the persistent fourth arch i.e. the first portion of the subclavian 

 artery. 



Carotid system (fig. 277). The dorsal aortce, now the internal carotids, are 

 seen at an early stage to be continued from the dorsal roots of the first arches 

 to the developing brain. Each divides into an anterior and a posterior branch. 

 The anterior stem ends at first in the mesial nasal process and afterwards in 

 the septum nasi. This terminal branch is, however, afterwards obliterated, and 

 the stem ends in the ophthalmic to the developing eye (the future central artery 

 of the retina), the anterior cerebral, and middle cerebral. The posterior branch 



