108 



PLATE LIV. 



MUSCLES 



A Pericardium. 



B Pleural sacs. 



C Thyroid gland. 



D Crico-thyroid muscles. 



E Scalenus anticus. 



F Scalenus medius. 



G Trachea. 



H Cricoid cartilage. 



K Anterior mediastinal glands. 



VESSELS 



n Left innominate vein. 

 b Eight innominate vein. 

 c Internal mammary veins. 

 d Inferior thyroid veins. 

 e Subclavian vein. 

 / Internal jugular. 

 g Middle thyroid vein. 

 h Mediastinal veins. 

 i Transverse aorta. 

 k Innominate artery. 

 I Arteria thyroidea ima. 



m Common carotid arteries. 



n Subclavian arteries. 



o Inferior thyroid branches of subclavian 



p Transverse cervical. 



r Supra-scapular. 



s Internal mammary. 



t Anterior intercostal and perforating 

 branches of internal mammary. 



v Anterior mediastinal branches of in- 

 ternal mammary. 



1 Eight pneumogastric. 



2 Phrenics. 



NERVES 



3 Cords of brachial plexus. 



Mr. Tredgold draws the following conclusions from a close investigation of the 

 ribs of ten genera of primates : (1) that there is a gradual but marked reduction in the 

 total number as we rise in the scale ; (2) that there is a coincident and proportionate 

 reduction in the number of the sternal ribs, and (3) that the 8th rib tends to change 

 from a sternal to a costal one, and consequently (4) the thoracic cavity is shortened, 

 but the capacity is compensated by an increase in breadth. 1 



1 Journal of Anatomy and Physiology, vol. xxx. p. 289. 



