Anatomy of Notoryctes typhlops. 99 



innominate vessel, the left subclavian having its origin some 

 little distance to the left of the left carotid artery, and not close 

 beside it, as in Man. In this, Notoryctes resembles the broad- 

 chested Marsupials, such as the Wombat and Koala.^ Consequent 

 on these variations the lengths of these vessels vary also. In 

 relation to the nerves, the carotid artery lies ventral to the recur- 

 rent laryngeal, and pneumogastric nerves, crossing them obliquely 

 as it runs outwards towards its anterior end. The sympathetic 

 nerve appears to lie quite to the other side of the coiiniion carotid 

 artery on each side. Where the two common carotids and the 

 right subclavian artery are united at their origin from the aorta 

 the pneumogastric also lies to the outer side of each common 

 carotid, since the angle caused l)y this vessel in its course for- 

 wards is then considerably greater than where the vessels of the 

 right side only are united to form an innominate vessel. The 

 common carotid gives off no branches, but divides anteriorly into 

 the external and internal carotids. The e.xternal carotid lies at 

 first slightly below and distinctly nearer the median line than the 

 internal carotid. It soon gives off the superior thyroid artery, 

 which runs straight forwards and inwards to the thyroid gland. 

 The ascending pharyngeal artery appears sometimes to be given 

 off from the internal carotid just anterior to the bifurcation of 

 of the common carotid, instead of being associated with the 

 external carotid, as in higher forms. A little in front of the 

 superior thyroid, the lingual artery is given off, running above 

 the digastric and stylo-hyoid muscles, and continues under the 

 mylo-hyoid muscles, giving off a branch to them, and then supplying 

 the tongue and contiguous parts. Just where the lingual artery 

 is given off, the external carotid turns outwards, curving round 

 behind the masseter muscle. On its posterior side, as it curves 

 round the articulation of the jaw, the external carotid gives off" 

 the occipital and posterior auricular arteries, while from its 

 anterior side is given off the facial artery, the main vessel then 

 breaking up into temporal and internal maxillary arteries. The 

 four last mentioned arteries leave the main trunk very close 

 together, the occipital arising about half way between these and 

 the origin of the lingual artery. It will thus be seen that the 



1 Owen : Anatomy of Vertebrates, vol. iii., p. 539. 



7a 



