S6 ELEMENTARY BIOLOGY. [CHAP. 



a. The external ca7'otid {lingual artery) to the 

 tongue and jfioor of the mouth; it and the com- 

 mon carotid together accompany the external 

 jugular vein. 



/5. The internal earotid; passing outwards and up- 

 wards to reach the deep-seated parts of the 

 head. Its branches accompany most of the 

 .factors of the internal jugular vein. 



y. The earotid gland ; a pigmented enlargement at 

 the base of /?. 



b. The middle or aortic arcJi: this is the largest of the 

 three: it runs round the throat towards the verte- 

 bral column, and unites with its fellow to form the 

 dorsal aorta (this may best be followed in detail 

 later). It gives off, on either side, at the level of 

 the arm. 



a. The subclavian artery ; mainly distributed to the 

 fore-limb. 



/?. The vertebral artery; arising immediately in the 

 front of a, and distributed to the vertebral 

 column and the back, together with the super- 

 ficial parts of the head and face (occipital 

 branch). 



c. The posterior or pulmonary arc/i ; it runs to the 

 root of the lung, giving off on its way a cutatieous 

 brarich which passes out to the integument of the 

 trunk, and supplies most of the blood which is 

 carried back by the great cutaneous vein. 



9. The dorsal aorta and its branches. 



Follow the aorta back; it will be found to run along 

 the middle line beneath the vertebral column giving 

 off in order 



