HEAD AND NECK OF THE HORSE 5 



which it is inserted in common with the sterno-hyoid muscle. In the 

 cranial half or more of the neck the omo-hyoid muscle lies between the 

 jugular vein and the common carotid artery. 



The small nerve of the muscle, derived from the first cervical, 

 should be sought a short distance from the hyoid attachment, 



A. CAROTIS COMMUNIS — As it lies ventral to the trachea at the 

 entrance to the chest, the bicarotid trunk divides into the right and left 

 common carotid ^ arteries. Each of these as it travels up the neck 

 crosses the line of the trachea very obliquely, so that, while the artery 

 at its commencement is ventral to the trachea, its termination is dorsal 

 to this tube. While the right artery is in contact medially with the 

 trachea, the left vessel is related also to the cesophagus. 



Running along the dorsal border of each common carotid artery is 

 the nerve cord formed by the vagus and the sympathetic, while along 

 the ventral border is the recurrent nerve. Dorsally each artery is in con- 

 tact with the longus colli and longus capitis muscles. The scalenus lies 

 lateral to the artery in the lower part of the neck, and the omo-hyoid 

 muscle is in a similar relation from the sixth (or fifth) cervical vertebra 

 onwards. As has already been noted, caudal to the fifth cervical 

 vertebra the carotid artery and the jugular vein lie together. 



The right and left common carotid arteries end on the wall of the 

 pharynx, about the level of the cricoid cartilage of the larynx, by divid- 

 ing into the occipital and the internal and external carotid arteries. 



The branches of the common carotid artery are as follows : — 



(1) Rami riiiiscidares. — Branches of varying size supply the 

 muscles ventral to the trachea, and the brachio-cephalic, longus colli, 

 longus capitis and scalenus muscles. 



(2) Rami ceso2)hagci and rami tracheale.s supply the oesophagus 

 and trachea respectively. 



(3) Very small rami lymphoglandulares supply the middle group 

 of cervical lymph glands. 



(4) A. parotidea. — An artery of considerable size supplies the 

 ventral part of the parotid gland. 



(5) A. thyreoidea (cranialis). — The thyroid artery is the largest 

 branch of the common carotid, from which it arises within a short 

 distance of the termination of this vessel. The artery pursues a curved 

 course round the cranial end of the thyroid gland, furnishing numerous 

 branches from the concave side of the curve to the gland itself and the 



^ KapuTLs (carotis) [Gr.], from Kdpos (caros), deep sleep. It is stated that the 

 ancients believed that sleep was induced by an increased flow of blood through the 

 arteries passing to the head. 



