STYLO-PHARYNGEUS MUSCLE. 107 



sels a loop of the first and second cervical nerves over the transverse 

 process of the atlas is to be defined ; and from it branches of communica- 

 tion are to be traced to the large ganglion of the sympathetic beneath the 

 artery, and to the vagus and hypoglossal nerves. Ascending to the 

 cranium, on the inner side of the carotid, the ascending pharyngeal artery 

 will be met with. 



To open the carotid canal in the temporal bone, and to follow the con- 

 tained artery into the cranium, make a cut along the side of the skull in 

 the following manner : the saw being placed beneath the mastoid process, 

 cut forwards to the foramen spinosum in the wing of the sphenoid bone 

 (to which spot the side of the skull has been already taken away), and let 

 the instrument be directed through the stylo-mastoid foramen and the root 

 of the styloid process, but rather external to the jugular foramen and the 

 carotid canal. AVhen the piece of bone has been detached, the carotid 

 canal may be opened with the bone forceps. 



In cleaning the artery in the canal, large and rather red branches of the 

 superior cervical ganglion of the sympathetic will be found on it ; and in a 

 fresh part two small filaments may be recognized with care one from 

 Jacobson's nerve, joining the sympathetic at the posterior part of the 

 canal ; the other from the vidian nerve, at the front of the canal. 



On the piece of bone that has been cut off, the dissector may prepare 

 very readily the tympanum with its membrane and chain of bones, and 

 the chorda tympani nerve. 



The internal carotid artery (fig. 25, <f) springs from the bifurcation of 

 the common carotid trunk. It extends from the upper border of the thy- 

 roid cartilage to the base of the skull ; then through the petrous portion of 

 the temporal bone ; and lastly along the base of the skull to the anterior 

 clinoid process, where it ends in branches for the brain. This winding 

 course of the artery may be divided into three parts : one in the neck, an- 

 other in the temporal bone, and a third in the cranium. 



Cervical part. In the neck the artery ascends almost vertically from 

 its origin to the carotid canal, and is in contact with the pharynx on the 

 inner side. The line of the common carotid artery would mark its posi- 

 tion in the neck. Its depth from the surface varies like that of the ex- 

 ternal carotid ; and the digastric muscle may be taken as the index of this 

 difference. Thus, below that muscle, the internal carotid is overlapped 

 by the sterno-mastoid and covered by the common teguments, fascia, and 

 the platysma, and is on the same level as the external carotid, though 

 farther back. But, above that muscle, the vessel is placed deeply beneath 

 the external carotid artery and the parotid gland, and is crossed by the 

 styloid process and the stylo-pharyngeus muscle. Whilst in the neck the 

 internal carotid lies on the rectus capitis anticus major muscle, which 

 separates it from the vertebrae. 



Vein. The internal jugular vein accompanies the artery, being con- 

 tained in a sheath with it, and placed on the outer side. 



Small vessels. Below the digastric muscle the occipital artery is 

 directed back over the carotid ; and the offset from it to the sterno-mastoi- 

 deus may run down on the carotid trunk. Above the digastric the poste- 

 rior auricular vessels cross the carotid. 



Nerves. The pneurnogastric is contained in the sheath between the 

 artery and vein, being parallel to them ; and the sympathetic, also run- 

 ning longitudinally, lies behind the sheath of the vessels. Crossing the 

 artery superficially, from below up, is the hypoglossal, which sends the 



