CAROTIDS, AND THEIR BRANCHES. 199 



the upper extremity of the sympathetic nerve, and gives one or 

 more small branches to the petrous bone; it also gives a few 

 branches to the dura mater and to the nerves about the caver- 

 nous sinus. But, for the full exposition of the distribution of the 

 internal carotid, see the arteries of the Brain and of the Eye. 



The External Carotid Artery (Carotis Externa) extends from 

 the termination of the primitive carotid, to the neck of the lower 

 jaw. In the early part of its course, where it is situated in front 

 of the internal carotid, and between the pharynx and the sterno- 

 mastoid muscle, it is comparatively superficial, being only enve- 

 loped by its sheath, and covered by the platysma myodes and 

 the skin. Just above this place it is crossed externally by the 

 hypoglossal nerve, which detaches the descending branch along 

 the front of its sheath and of that of the primitive carotid. Some- 

 what above this nerve, it is also crossed externally by the digas- 

 tric and the stylo-hyoid muscle, and lies there on the side of the 

 superior constrictor muscle of the pharynx, near the tonsil gland. 

 About its middle, it is crossed internally by the stylo-glossus and 

 the stylo-pharyngeus muscle ; it then ascends through the sub- 

 stance of the parotid gland, between the ramus of the lower 

 jaw and the ear, to its termination. 



Several very important branches are given off from the ex- 

 ternal carotid ; they are as follow : 



The Superior Thyroid Artery (Art. Thyroidea Superior) arises 

 from the external carotid, about a line above its root, and is dis- 

 tributed to the larynx and to the thyroid gland. It goes at first 

 inwards and forwards on the side of the larynx, being covered 

 by the omo-hyoideus muscle, and by the platysma myodes; it 

 then descends under the sterno-thyroideus to the upper margin 

 of the lobe of the thyroid gland. In this course it performs 

 .several flexuosities, of considerable variety, in different indivi- 

 duals. 



The Laryngeal Branch comes from it near the superior mar- 

 gin of the thyroid cartilage; this branch glides in between the 

 thyreo-hyoid muscle and the middle thyreo-hyoid membrane or 

 ligament; after a short course, it penetrates the latter, and is then 

 distributed in a gfeat number of small twigs to the muscles and 

 to the lining membrane of the larynx. A small trunk, either 



