598 THE EMBRYOLOGY OF THE FROC. 



as the pharyngeal artery, while, as mentioned above, the hyoidean vein 

 disappears with the oral sucker. 



The Anterior, or Internal Carotid Arteries (Fig. 345, car). These 

 are the extensions of the lateral dorsal aortae into the head. 



Commissural arteries (Fig. 345, ac). These are the two transverse 

 connections between the internal carotids, which pass anterior and pos- 

 terior to the infundibulum. 



Lingual, or External Carotid Arteries (Fig. 345, 1.). These appear 

 before the time of the mouth opening as a pair of sinuses in the buccal 

 cavity. As the mouth opens, they extend backward to connect with the 

 ventral ends of the efferent branchial arteries of the first branchial arch 

 at the point where the carotid gland is to develop. 



Changes in Aortic Arches. As soon as the gills disappear, there 

 must naturally be a great modification in the branchial aortic arches 

 (Fig. 345). 



Carotid Arch. As already stated, a continuous aortic arch is re- 

 established in each of the four branchial arches when the afferent and 

 efferent arteries fuse. The first branchial aortic arch, which is the third 

 arch of the entire series, remains as the carotid arch. 



Systemic Arch. The lateral dorsal aorta between the carotid arch 

 and the aortic arch immediately posterior to it, is reduced to a solid 

 strand of connective tissue and no longer functions, so that the second 

 pair of aortic arches (the fourth of the whole series) form the roots of 

 the dorsal aorta and are called the systemic arches. 



Pulmocutaneous Arch. The third aortic arch (the fifth of the whole 

 series) also becomes a solid strand of tissue and then disappears entirely, 

 while the fourth (the sixth of the whole series) becomes the pulmo- 

 cutaneous arch. 



Pulmonary Arteries. These appear just after hatching as small out- 

 growths from the upper ends of the efferent branchial arteries of the 

 fourth branchial arch, which then extend backward to the lung rudi- 

 ments. 



Cutaneous Arteries. These leave the pulmonary arteries and extend 

 dorsally to spread out over the skin of both sides and back. 



Ductus Botalli. This, it will be remembered, from our study of the 

 chick, is that part of the fourth aortic arch between the lateral dorsal 

 aorta and the origin of the pulmonary arteries (Fig. 345). This portion 

 slowly atrophies and also becomes a solid strand. Three channels are 

 now formed in the truncus arteriosus by various septa which divide it 

 longitudinally. The carotid arches lead from one of these channels, 

 which receives blood from the left side, while another carries venous 

 blood from the right side of the heart to the pulmocutaneous arches. 

 The remaining one connects the systemic arches. 



