26 THE FROG 



into three aortic arches (131, 135, 138). (See also 

 p. 22.) 



131. The most anterior of the aortic arches is the common 

 carotid which soon divides to form 



132. the external carotid (lingual) artery, running to 

 the lower jaw and ventral structures of the head, and 



133. the internal carotid artery, a larger branch, running 

 to the dorsal side of the head. 



134. Note, at the juncture of these arteries, an oval dila- 

 tion, the carotid gland. 



135. The most posterior of the aortic arches is the pulmo- 

 cutaneous, which divides into 



136. a pulmonary artery to the lung and 



137. a great cutaneous artery to the skin. 



138. The middle arch is the systemic, which bends dor- 

 sally around the pharynx to unite with its mate from 

 the opposite to form 



139. the dorsal aorta, lying just ventral to the vertebral 

 column. From the systemic arches spring four 

 branches, 



140. the laryngeal artery, to the larynx, 



141. the occipito-vertebral artery to the skull and verte- 

 bral column, 



142. The oesophageal artery, to the oesophagus, and 



143. by far the largest, the subclavian artery. This 

 vessel extends laterally and supplies the arm. // 

 time permits, trace its branches. 



Caudad of the union of the systemic aortic arches by which 

 the dorsal aorta is formed, note the departure of the 

 cceliaco-mesenteric artery (61) and behind this, in se- 

 quence: 



144. four to six urogenital arteries supplying the kidney, 

 fat body, ovary or testis. 



