THE THORAX 1365 



Cervical ribs. — It occasionally happens that the rib element of the seventh 

 cervical vertebra, normally fused wdth the true transverse process, is segmented off 

 as a separate, though usually rudimentary, rib. This anomaly is generally 

 bilateral. It occurred in 3 of 260 subjects (1.16 per cent.) examined by Wingate 

 Todd.* 



The anterior extremity of a cervical rib may, according to the degree of its development 

 (1) lie free amongst the scalene muscles; (2) be connected with the sternum by a ligamentous 

 prolongation; (3) articulate with the upper surface of the first thoracic at about its centre by 

 a synchondrosis, or (4) form a complete rib, articulating by a costal cartilage with the sternum. 



The lowest trunk of the brachial plexus formed by the eighth cervical and first thoracic 

 roots, the subclavian artery and less commonly the subclavian vein, curve over the upper 

 surface of these ribs. The abnormality owes its clinical importance to the pressure effects 

 produced on the nerve trunk in a small proportion of the cases. This pressure is manifested 

 by (1) pain, going on to anaesthesia down the medial side of arm, forearm and hand; (2) paralysis 

 of the intrinsic muscles of the hand, producing the main en griffe, and to a less extent of the mus- 

 cles of the forearm; (3) vascular effects (anaemia, gangrene, etc.), manifested chiefly in the hand. 

 Todd has shown that these vascular effects are not due to mechanical pressure on the subclavian 

 artery by the cervical rib as was formerly supposed, but are trophic lesions of the sympathetic 

 (vasomotor) nerves. The vasomotor nerves to the arm mainly come from the second thoracic 

 root by the communication it gives to the lowest cord of the brachial plexus, and so are exposed 

 to pressure from the rib. 



Fig. 1105. — Cervical Rebs, Viewed from Above. (X 2-) NN, Impression for Lowest 

 Trunk of Brachial Plexus. AA, Impression for Subclavian Artery. (T. Wingate 

 Todd.) 



The same investigator has shown that similar symptoms may be produced occasionally by 

 a first thoracic rib in cases where the brachial plexus has migrated caudad. In the living 

 patient, unless a radiogram be taken showing all the vertebrae up to the base of the skull, it is 

 not possible with precision to ascertain with which vertebra the highest rib present articulates. 



Structures found in an intercostal space. — (1) Skin; (2) superficial fascia, 

 with cutaneous vessels and nerves; (3) deep fascia; (4) external intercostal; (5) 

 cellular interval between intercostals, containing trunks of intercostal vessels and 

 nerves; (6) internal intercostals; (7) thin layer of fascia; (8) subpieural connective 

 tissue; (9) pleura (fig. 1106). 



The intercostal arteries are nine aortic and two from the superior intercostal. An aortic 

 intercostal having given off its dorsal branch, lying beneath the plem-a, crosses the space ob- 

 liquely upward to gain the lower border of the rib above, enters the costal groove at the angle, 

 and runs forward between the intercostal muscles to anastomose with the anterior intercostals 

 from the internal mammary or musculo-phrenic. Hence the rule of making the incision in 

 empyema above the upper margin of the lower rib and in front of the angle. Along the dorsal 

 branch a vertebral abscess may track backward. 



Internal mammary artery. — This descends behind the clavicle, the costal 

 cartilages, and the first six spaces, about 1.2 cm. (| in.) from the edge of the ster- 

 num. In the sixth intercostal space it divides into musculo-phrenic and superior 

 epigastric acteries. Its venae comitantes uniting join the innominate vein of the 

 same side. A punctured wound of the artery is most easily secured in the second 

 and third spaces; below, resection of part of a costal cartilage will be needed. 



Structures passing through the upper aperture of the thorax. — If a section 

 is made passing through the manubrium sterni, upper border of the first rib, and 



* Journal of Anatomy and Physiologj', Vol. 47, 1913. 



