THE HEAD AND NECK iii3 



place freely between the external and internal carotid arteries of 

 opposite sides. (2) The inferior thyroid artery of the side operated 

 upon anastomoses freely with the superior thyroid of the same side, 

 which is a branch of the external carotid. (3) The deep cervical 

 branch of the superior intercostal, which latter is a branch of the 

 second part of the subclavian artery on the right side, and of the 

 first part on the left side, anastomoses with the ramus cer\dcaJis 

 princeps of the occipital, which is a branch of the external carotid. 

 (4) The vertebral artery undergoes much enlargement. 



Carotid Body or Ganglion. — This small body is situated behind 

 the common carotid artery close to its bifurcation. It is composed 

 of a few lobules, united by connective tissue, and it receives minute 

 twigs from the adjacent part of the common carotid artery. The 

 lobules consist of groups of polyhedral cells, permeated by blood- 

 capillaries and sympathetic nerve-filaments. Some of the cellular 

 constituents are chromaffin cells, similar to those which are met with 

 in the medulla of the suprarenal body and in the sympathetic 

 gangHa. These cells are derived from the contiguous ganglia of the 

 sympathetic system. The carotid body of each side is similar to the 

 coccygeal body and organs of Zuckerkandl. 



The carotid body may be regarded as being developed in part from the 

 sympathetic system, and as belonging also to the lymphatic system. 



Development. — The common carotid arteries are developed from the parts of 

 the ventraJ aortae which are situated between the third and fourth arterial arches. 



Internal Jugular Vein. — ^The internal jugular vein is the con- 

 tinuation of the intracranial lateral sinus. It commences in the 

 postero-extemal compartment of the jugular foramen, and termi- 

 nates behind the inner end of the clavicle by joining the subclavian 

 vein to form the innominate vein. At its commencement it presents 

 a slight dilatation, called the bulb. The vein descends vertically, 

 lying at first on the outer side of the internal carotid artery, and 

 subsequently on the outer side of the common carotid artery, 

 the pneimiogastric nerve being interposed in each case, and all 

 being enclosed within the carotid sheath. The relations of the 

 vessel for the most part correspond to those of the arteries which 

 it accompanies. 



Tributaries. — ^These are as follows : 



Inferior petrosal sinus. Pharyngeal. 



Common facial. Superior thyroid. 



Lingual. Middle thyroid. 



A small vein accompanying the occipital artery may occasionally 

 open into it. 



The inferior petrosal sinus leaves the cranial cavaty through the 

 antero-mtemal compartment of the jugular foramen, and opens into 

 the internal jugular vein close to the base of the skull. 



Development. — The internal jugular vein is developed from the anterior 

 cardinal or primitive jugular vein. 



