1360 HUMAN ANATOMY. 



joins the superficial cardiac plexus. In some instances the nerve remains behmd the 

 carotid artery and joins the deep cardiac plexus. 



A pretracheal branch, derived from the loop between the superior cervical 

 cardiac nerve and the inferior laryngeal, descends anterior to the trachea and is dis- 

 tributed to the pericardium and the anterior pulmonary plexus (Drobnik. ) 



The superior cervical cardiac nerve communicates freely in the neck with the 

 middle cardiac and other branches of the sympathetic, and with the external laryngeal 

 and superior cervical cardiac branches of the vagus. In the thorax it inosculates 

 with the inferior laryngeal nerve. 



Variations. — The superior, as well as the other cardiac nerves, presents a considerable 

 degree of variation, sometimes to so grea; an extent as to show no resemblance to the accepted 

 typical plan of arrangement. It is sometimes absent, especially on the right side, and in such 

 event appears to be replaced by a branch from the vagus or from the external laryngeal nerve. 

 It may have no independent course, but join one of the other sympathetic cardiac nerves and 

 reach its destination as a part of the latter. 



3. The vascular branches comprise plexiform nerve-structures which accom- 

 pany the terminal divisions of the common carotid artery. They consist of : (a) the 

 external cai-otid branch and {b) the internal carotid branch. 



a. The external carotid branch (n. caroticus externus) (Fig. 1061) joins 

 the external carotid artery and furnishes subsidiary plexuses which accompany the 

 branches of that vessel. In addition to supplying vasomotor fibres to the external 

 carotid tree, sympathetic filaments are furnished to two of the ganglia of the trigem- 

 inal nerve. A branch (radix g. submaxillaris) from the plexus on the facial artery 

 (plexus maxillaris externus) joins the submaxillary ganglion as its sympathetic 

 root, and one or more, the smallest deep petrosal nerve, from the plexus on 

 the middle meningeal artery (plexus meningeus), forms the sympathetic root of the 

 otic ganglion. 



Ganglia of microscopic size have been described on these vascular plexuses. 

 The most important of these, the ternporal ganglion, is situated on the external 

 carotid at the point of origin of the posterior auricular artery and is said to receive 

 a filament of communication from the stylo-hyoid branch of the facial nerve. 



b. The internal carotid branch (n. caroticus internus) is apparently an 

 upward, cranial extension of the superior ganglion (Fig. 1061). Ascending beneath 

 the internal carotid artery, it accompanies that vessel into the carotid canal, where it 

 divides into two plexuses, the carotid and the caveriioiis, the former ramifying on the 

 lateral and the latter on the mesial aspect of the artery. While the individuality of 

 these two is distinct, there are numerous fine fibres connecting them as they pass 

 upward into the cranium. 



The carotid plexus (plexus caroticus internus) is located on the lateral or outer 

 surface of the internal carotid artery at its second bend. In addition to supplying 

 line plexuses which accompany the branches of the artery to their ultimate ramifica- 

 tions, the following arise from the carotid plexus : (a«) the carotid branches, {bb^ 

 the communicating branch to the abducent nerve, (^cc^ the commiaiicating bj'anches 

 to the Gasserian ganglion, (^dd ) the great deep petrosal nerve and (^(?) the small 

 deep petrosal nerve. 



aa. The carotid branches consist of numerous fine twigs which are supplied to the internal 

 carotid artery. 



bb. The communicating branch to the abducent nerve consists of one or two twigs which 

 join the nerve as it lies in the wall of the cavernous sinus in close proximity to the internal 

 carotid artery. 



cc. The communicating branches to the Gasserian ganglion comprise several small fila- 

 ments which pass to the ganglion ; they usually arise from the carotid but sometimes are derived 

 from the cavernous plexus. 



dd. The great deep petrosal nerve courses forward to the posterior end of the Vidian canal, 

 where it joins the great superficial petrosal to form the Vidian nerve (page 1059), finally en- 

 tering Meckel's ganglion as its sympathetic root. 



ee. The small deep petrosal nerve or n. carotico-tympanicus joins the tympanic plexus 

 (page 1075), a structure formed by the tympanic branch of the glosso-phar^-ngeal, a filament 

 from the geniculate ganglion of the facial nerve and the small deep petrosal nerve. In addition 



