1014 THE NERVE SYSTEM 



passes forward between the vein and artery, and lower down in the neck becomes 

 superficial below the Digastric muscle. The nerve then loops around the occipital 

 artery, and crosses" the external carotid and its lingual branch below the tendon 

 of the Digastric muscle. It passes beneath the tendon of the Digastric, the 

 Stylohyoid, and the ftlylohyoid muscles, lying between the last-named muscle 

 and the Hyoglossus (Fig. 748), and communicates at the anterior border of the 

 Hyoglossus with the lingual nerve (Fig. 747); it is then continued forward in the 

 fibres of the Geniohyoglossus muscle as far as the tip of the tongue, distributing 

 branches to its muscle substance. 



Branches of Communication (Fig. 747). The branches of communication are 

 with the 



Vagus. First and second cervical nerves. 



Sympathetic. Lingual. 



The communication with the vagus takes place close to the exit of the nerve 

 from the skull, numerous filaments passing between the hypoglossal and the gan- 

 glion of the trunk of the vagus through the mass of connective tissue which unites 

 the two nerves. It also communicates with the pharyngeal plexus by a minute 

 filament as it winds around the occipital artery. 



The communication with the sympathetic takes place opposite the atlas by 

 branches derived from the superior cervical ganglion, and in the same situation 

 the nerve is joined by filaments derived from the loop connecting the first two 

 cervical nerves. 



The communication with the lingual nerve takes place near the anterior border 

 of the Hyoglossus muscle by numerous filaments which ascend upon it. 



Branches of Distribution (Fig. 747). The branches of distribution are: 



Meningeal or Dural. Thyrohyoid. 



Descendens hypoglossi. Muscular. 



Of these branches, the descendens hypoglossi and the branches to the Infra- 

 hyoid muscles are not actually derived from the hypoglossal nerve, but, as is 

 shown in Fig. 747, are branches from the loop formation (better called ansa 

 cervicalis) of the first with the second and third cervical nerves. A part of the 

 loop, commonly called the descendens hypoglossi, is enclosed, for a short distance, 

 in the sheath which invests the hypoglossal nerve. 



Meningeal or Dural Branches (Fig. 705). As the hypoglossal nerve passes 

 through the anterior condylar foramen it gives off, according to Luschka, several 

 filaments to the dura in the posterior fossa of the base of the skull. 



The Descendens Hypoglossi (ramus descendens) (Figs. 747 and 748) is a long 

 slender branch, which leaves the hypoglossal where it turns around the occipital 

 artery. It consists mainly of fibres which pass to the hypoglossal nerve from the 

 first and second cervical nerves in the above-mentioned communication. It 

 descends in front of or within the sheath of the common carotid artery, giving 

 off a branch to the anterior belly of the Omohyoid, and then joins the communi- 

 cating branches from the second and third cervical nerves, just below the middle 

 of the neck, to form a loop, the ansa hypoglossi. From the convexity of this loop 

 branches pass to supply the Sternohyoid, Sternothyroid, and the posterior belly 

 of the Omyhyoid. According to Arnold, another filament descends in front of 

 the vessels into the thorax, and joins the cardiac and phrenic nerves. 



The Thyrohyoid Branch (ramus thyreohyoideus) (Fig. 747) is a small branch 

 arising from the hypoglossal near the posterior border of the Hyoglossus; it 

 >asses obliquely across the great cornu of the hyoid bone and supplies the Thyro- 



ivoid 



