mi. J. MUKIE ON THE ANATOMY OP THE SEA-LION. 537 



proceeds forward with a usual course outside the trachea ; its subsequent distribution 

 will be included with that of the left side, which it resembles. 



Common carotid and branches. — The left common carotid, as thick as a swan's quill, 

 springs, as mentioned, from the middle and back part of the aortic arch, and crossing 

 over the left bronchus continues alongside of the trachea for a distance of 9 inches, 

 when it gives off the superior thyroid. This is a small branch, less than 2 inches 

 long, which curves inwards below the internal jugular vein, opposite the posterior 

 inferior angle of the cricoid cartilage, and splits into three branchlets. One of these 

 runs down the surface of the oesophagus, and sends four short arched twigs to the 

 diminutive thyroid body. The second passes deeply between the thyroid gland and the 

 trachea, supplying the latter. The third divides immediately beyond its origin, a twig 

 entering the upper end of the thyroid gland, another being sent to the outer side 

 of the sterno-thyroid muscle as it lies on the cricoid cartilage. Besides, minute 

 vascular twigs pierce the muscular wall of the oesophagus, and arc also freely distributed 

 to the tissues intervening between the latter and the trachea, and also partly to the 

 crico-thyroid and inferior constrictor muscles. The superior laryngeal artery is derived 

 directly from the trunk of the common carotid, and is not a branch of the superior 

 thyroid, as is more usually the case in Man. It leaves the common carotid about 

 2 inches apart, or anterior to the superior thyroidal branch, and from the opposite side 

 of the vessel. At its origin the superior laryngeal artery is placed upon the outer 

 aspect of the thyro-hyoid muscle, and, crossing a portion of the inferior constrictor 

 gains the interspace between that muscle and the middle constrictor, where it accom- 

 panies the superior laryngeal nerve. The hindermost of the parotidean arteries is 

 another small offshoot from the common carotid instead of the external carotid. It 

 springs from the inner or lower side of its parent trunk, an inch distant from the 

 superior laryngeal artery, and, running across the middle constrictor muscle, penetrates 

 the parotid gland posteriorly and on its inner surface. The second and anterior 

 parotidean twig is as long but scarcely so large as the posterior one ; it is derived 

 from the angle of division of the common into internal and external carotids, as noted 

 below. 



External carotid artery and its subdivisions. — The common carotid J of an inch 

 beyond the first parotidean twig above described, just below and posterior to the 

 osseous stylo-hyal and stylo-pharyngeus muscle, divides into two main trunks of equal 

 calibre, the external and internal carotid arteries. At the angle where these divaricate 

 several small arterial branches, muscular and glandular, are given off. The former 

 supply the middle constrictor, stylo-pharyngeus and adjoining muscles ; the latter is the 

 second parotidean twig mentioned above. 



The lingual artery, of moderate thickness, arises about an inch from the commence- 

 ment of the external carotid, and, pursuing a course parallel with and crossed by the 

 lingual nerve, supplies the tongue from its body to the tip. At first it lies on the superior 



