THE COMMON CAROTID ARTERY 



637 



superficially with the jugular vein, but further forward the omo-hyoideus muscle 

 intervenes between the artery and vein. Near its termination the artery becomes 

 more deeply placed and is related laterally 

 to the mandibular and parotid glands, medi- 

 ally to the ossophagus. In some cases it is in 

 contact ventrally with the lateral lobe of the 

 thyroid gland, especially when the latter is 

 more dorsally situated or larger than usual. 

 The left common carotid artery (A. 

 carotis communis sinistra) differs from the 

 right one in that it is related deeply to the 

 cesophagus also, which usually separates it 

 from the trachea in part of its course. 



The left carotid is commonly in contact with 

 the trachea for a short distance (ca. 8-10 cm.) at the 

 root of the neck, but this contact may be even less 

 when the oesophagus is more ventral than usual and 

 the bicarotid trunk long. On the other hand, the re- 

 lation to the trachea may be more extensive. 



The collateral branches of the common 

 carotids are in the main small. They com- 

 monly comprise the following: 



1. Muscular branches (Rami muscu- 

 lares) of variable size go to the ventral 

 muscles of the neck and the skin. 



2. (Esophageal and tracheal branches 

 (Rami cesophagei et tracheales). Small 

 twigs go to the cervical lyriiph glands also. 



3. The parotid artery (A. parotidea) 

 comes off near the termination and enters 

 the ventral part of the parotid gland. It 

 also sends twigs to the adjacent lymph 

 glands, and sometimes detaches a branch to 

 the mandibular gland. It is inconstant. 



4. The anterior thyroid or thyro-laryn- 

 geal artery (A. thyreoidea cranialis), the 

 largest collateral branch of the carotid, 

 arises from the latter two or three inches 

 before it divides. It curves over the anterior 

 end of the thyroid gland, into which it sends 

 several branches. It gives off the laryngeal 

 artery (A. larjmgea), which sends branches 

 to the external muscles of the larynx and the 

 constrictors of the pharynx, passes between 

 the cricoid and thyroid cartilages, and sup- 

 plies the internal muscles and the mucous 

 membrane of the larynx. A small pharyn- 

 geal branch (A. pharyngea ascendens) runs 

 upward and forward to the crico-pharyn- 

 geus, and supplies twigs to the posterior 

 part of the pharynx and the origin of the 

 oesophagus. Small innominate twigs are 



given off to the trachea, the oesophagus, and the sterno-thyro-hyoideus and omo- 

 hyoideus muscles. 



Fig. 557. — Cross-section of Nece of Horse, 

 Passing through Fifth Cervical Ver- 

 tebra; Anterior \'iew. 



a. Branches of cervical nerves; a', nuchal fat; 

 b, intertransversalis muscle; c, longissimua mus- 

 cle; d, vertebral artery; e, vertebral vein; /, ner- 

 vus trans"\'ersarius; g, spinal accessory nerve (dor- 

 sal division); h, recurrent nerve; i, vago-sympa- 

 thetic trunk; k, tracheal b'mph duct; /, body of 

 fifth cervical vertebra; /', transverse process of 

 same; m, common carotid artery; n, jugular vein; 



0, deep cervical artery; o\ satellite vein of o; 

 p, spinal cord; q, dura mater; r, spinal vein; s, 

 ligamentum nucliEe; t, rhomboideus muscle; u, 

 splenius; v, complexus; w, multifidus; x, serratus 

 cervicis; y, brachiocephalicus; z, sterno-cephali^jts; 



1, rectus capitis ventralis major; S, omo-hyoideus ; _ 

 S, cutaneus; 4> sterno-thyro-hyoideus; 6, longus 

 colli; 6, 7, longissimus capitis et atlantis; 8, trape- 

 zius; 9, spinalis; 10, oesophagus; 11, trachea, with 

 cartilaginous ring (11'), mucous membrane {11"), 

 and muscular layer (11'"). (After EUenbferger, 

 in Leisering's Atlas.) 



