GREAT VESSELS AND NERVES OF NECK 213 



it at the level of the lower border of the posterior belly of the 

 digastric, the posterior auricular, at the level of the upper 

 border of that muscle, and the sterno-mastoid branch of the 

 occipital artery at the point where the hypoglossal nerve 

 turns forwards. 



The relationship of the external carotid artery to the 

 internal carotid is a varying one. At first the external 

 carotid lies antero-medial to the internal carotid ; but soon, 

 owing to its inclination backwards, it comes to lie superficial 

 to the internal carotid. The following structures intervene 

 between the two vessels : 



1. Styloid process. 



2. Stylo-pharyngeus muscle. 



3. Glosso-pharyngeal nerve. 



4. Pharyngeal branches of vagus 



and sympathetic. 



5. A portion of the parotid gland. 



Posterior to the internal carotid are the longus capitis 

 (O.T. rectus capitis anticus major) and the sympathetic 

 trunk ; postero-laterally are the glosso-pharyngeal, the vagus, 

 the accessory and the hypoglossal nerve ; and still more 

 laterally and posteriorly is the internal jugular vein. On 

 its medial aspect the internal carotid is related to the con- 

 strictors of the pharynx, the ascending pharyngeal artery and 

 the levator veli palatini. 



Before leaving the internal carotid artery, note that, 

 near the base of the skull, four nerves appear in the interval 

 between it and the internal jugular vein ; they are the glosso- 

 pharyngeal, the vagus, the accessory, and the hypoglossal. 



Vena Jugularis Interna. The internal jugular vein is the 

 largest venous channel of the neck. It enters the neck through 

 the postero-lateral compartment of the jugular foramen, where 

 it is directly continuous with the transverse blood sinus of 

 the cranium. From the jugular foramen it proceeds down- 

 wards, until it reaches the posterior aspect of the medial end 

 of the clavicle, where it joins the subclavian vein to form the 

 innominate vein (Fig. 78). Its commencement in the jugular 

 foramen shows a slight dilatation, termed the bulb, the lumen of 

 which remains at all times patent owing to the connection of 

 walls of the bulb to the margins of the foramen. The skull cap 

 should be removed and a probe should be passed from the 

 transverse sinus into the internal jugular vein, to demonstrate 

 the continuity of the two channels. 



Relations. At its commencement the internal jugular 



m 14 & 



