T43 HUMAN ANATOMY. 



to the body next below it. With the fourth or fifth thoracic they point much more 

 strongly downward, so as to be opposite the disk below the succeeding body. This 

 continues to the tenth, where they are opposite the body below. In the loins the 

 spines have a considerable posterior surface, which is opposite the disk and the 

 upper part of the body below it. The tips of the spines are not always in a straight 

 line, but sometimes describe a zigzag. The transverse process of the atlas can be 

 felt below the tip of the mastoid process, moving with the head when the latter is 

 turned. The transverse processes below this are felt with great difficulty through 

 the muscles of the side of the neck. Those of the back and loins are too thickly 

 covered to be felt. The laminae are also thickly covered with muscles, so that the 

 operation of laminectomy necessarily involves a deep wound, and in the thoracic 

 region this difficulty is increased by the backward projection of the ribs. 



As landmarks the spines of the vertebrae, on account of their accessibility, have 

 great value. These spines have the following relations. The fourth cervical spine 

 corresponds to (i) the opening of the larynx ; (2) the bifurcation of the carotid 

 artery, and hence the point of origin of both the external and internal carotid 

 arteries. The sixth cervical indicates the level of the carotid tubercle (transverse 

 process of the sixth vertebra) and the entrance of the vertebral artery into the bony 

 canal. The seventh cervical spine is a guide to (i) the lower border of the cricoid 

 cartilage ; the lower opening of the larynx and the beginning of the trachea ; (2) 

 the lower end of the pharynx and the upper opening of the oesophagus ; (3) the 

 crossing of the omo-hyoid over the common carotid ; (4) the level of the apex of 

 the lung and to the summit of the arch of the subclavian artery. The fourth thoracic 

 spine corresponds to the level at which the aorta reaches the spinal column, the 

 trachea bifurcates, and posteriorly the apex of the lower lobe of the lung is found. 

 It is on the same level as the root of the spine of the scapula. The seveyith thoracic 

 lies on a level with the inferior angle of the scapula. The eighth thoracic indicates 

 the lower level of the heart and that of the central tendon of the diaphragm and the 

 level at which the inferior vena cava passes through the diaphragm. The 7iinth tho- 

 racic marks the level at which the upper edge of the spleen is found in health, and at 

 which also the oesophagus pierces the diaphragm. The tenth thoracic corresponds 

 to the lower edge of the lung, the spot at which the liver comes to the surface poste- 

 riorly. The spines of the third to the ninth thoracic correspond to the heads of the 

 fourth to the tenth ribs respectively. The eleventh thoracic is a guide to the normal 

 situation of the lower border of the spleen and to the upper part of the kidney. 

 The twelfth thoracic marks the lower limit of the pleura, the passage of the aorta 

 through the diaphragm, and the situation of the pyloric end of the stomach, and 

 is on a level with the head of the last rib. The first lumbar spine is on the line of 

 the renal arteries and the pelvis of the kidney. The second lumbar spine corre- 

 sponds to (i) the termination of the duodenum and the commencement of the 

 jejunum ; (2) the opening of the ductus communis choledochus into the intestine ; 

 (3) the lower border of the kidney ; (4) the lower border of the pancreas ; (5) the 

 upper end of the root of the mesentery ; (6) the point of origin of the superior 

 mesenteric artery ; (7) the commencement of the thoracic duct ; (8) the commence- 

 ment of the vena porta ; (9) the termination of the spinal cord and the origin 

 of the Cauda equina; (10) the upper end of the receptaculum chyli. The third 

 lumbar corresponds to the level of the umbilicus and the origin of the inferior 

 mesenteric artery ; the fourth lumbar spine marks the point of bifurcation of the 

 abdominal aorta into the two common iliac arteries, and lies on a level with the 

 highest part of the ilium ; and, finally, the fifth lumbar spine is a little below the 

 beginning of the inferior vena cava. 



Direct cocainization of the spinal cord has recently been employed in surgery in 

 operations on the lower abdomen, pelvis, and lower extremities. The injection into 

 the subarachnoid space surrounding the cord is made through the space between 

 the fourth and fifth lumbar vertebrae. To find this space, draw a line connecting 

 the highest points of the crest of the ilium posteriorly. This will pass through the 

 spine of the fourth lumbar vertebra. The point for injection is one centimetre below 

 and one centimetre to the outer side of the point at which the transverse line crosses 

 the vertebral spine in the median line. 



