iio8 



A MANUAL OF ANATOMY 



(ansa hypoglossi). The convexity of the loop is directed downwards, 

 and from it branches are given off to (i) the sterno-hyoid, (2) the 

 stemo-thyroid, and (3) the posterior belly of the omo-hyoid, 

 muscles. 



The fibres of the descendens cervicis nerve are regarded as being of spinal, 

 act hypoglossal, origin. 



For the rami communicantes cervicis, see Cervical Plexus. 



Thyro-hyoid Nerve. — ^This nerve, which is composed of spinal 

 fibres, derived from the loop between the first and second cervical 

 nerves, arises from the hypoglossal at the lower border of the 



GH& 



I.J.V. P.N. S.N. 



,o.H. Fig. 45 IB. — Carotid 



Sheath. 



I.J. v., internal jugular vein; P.N., 

 pneumogastric nerve; S.N., sym- 

 pathetic nerve ; C.C.A., common 

 carotid artery; C.S., carotid sheath ; 

 S., septum ; D.C.N., descendens 



Fig. 451A. — Scheme of the Hypoglossal cervicis nerve. 

 Nerve, showing its Conkections with 

 Cervical Spinal Nerves. 



Sy., twig from sympathetic ; Pn., communicating with 

 pneumogastric ; ic, ac, 3c, first, second, and third cer- 

 vical ; C.H., oommunicans hypoglossi ; C.C., communi- 

 cantes cervicis; D.C., descendens cervicis; A.B.O.H., to 

 anterior belly of omo-hyoid ; A.C., ansa cervicis; S.H., 

 to sterno-hyoid ; S.T., to stemo-thyroid ; P.B.O.H., to 

 posterior belly of omo-hyoid; T.H., to thyro-hyoid; 

 G.H., to genio-hyoid ; G.H.G., to genio-hyo-glossus ; 

 H.G.. to hyo-glossus ; S.G., to stylo-glossua. 



posterior belly of the digastric. It passes forwards and downwards, 

 forming an acute angle with the parent trunk, and it disappears 

 beneath the posterior border of the thyro-hyoid muscle, immediately 

 after which it enters its deep surface. 



Carotid Sheath. — The carotid sheath, as stated in connection 

 with the deep cervical fascia, is derived from the posterior lamina 

 of the sheath of the stemo-cleido-mastoid muscle, and is intimately 

 connected anteriorly with the pretracheal process, and posteriorly 

 with the prevertebral process, of the deep cervical fascia. The 

 interior of the sheath is divided into three compartments — outer. 



