SOCIETY OF THE UNIVKli.SITY OF ABKliDEEN. 7 



and if one assumes that two adjoining spines separate to the extent of | ! in., 

 the interval between the laminae increases by a half to two-thirds of that 

 distance, that is -| in. to J- in., since the axis of rotation is a transverse 

 one approximately through the middle of the intervertebral disc. The base 

 of the triangular interval is therefore movable. In order to get the largest 

 space possible, the patient is bent forward when the puncture is being made. 

 The space bears a considerable resemblance to the perineal segment of the 

 pelvic outlet and between the upper and lower lumbar regions are differences 

 which correspond very closely to the differences between the male and female 

 pubic arch. The width of the interval depends on the distance apart of the 

 two lower articular processes of the upper vertebra, and this varies in different 

 persons. As is known, it frequently increases steadily from the first to the last 

 lumbar vertebra, and the spaces broaden out accordingly. The width is often 

 about the same in the 2nd, 3rd and 4th interspaces varying from in. to over 

 f in., the average being almost f in. Between the 4th and 5th lumbar and 

 between the 5th lumbar and 1st sacral vertebrae, the width in the bones 

 examined lay between in. and 1-J in. 



For ordinary lumbar puncture, the needle is introduced usually opposite 

 the interval between the 3rd and 4th spine, in. to in. to one side of the 

 middle line in order to clear the spinous processes. It is pushed in with a 

 slight inclination upwards and inwards, aiming at reaching the middle line 

 at a point about 1 in. to If in (4 to 4'5 cm) deep from the tip of the nearest 

 spinous process. The patient should have the spine bent and may be either 

 sitting or lying on one side. The needle passes smoothly through the mass of 

 the Erector Spinae muscle with its tendinous bands, and meets with first 

 somewhat increased and then diminished resistance as it passes through the 

 Ligamentum Subflavum. In one case out of 17, the vertebrae and spinous 

 processes were so altered by pathological bony excrescences, that there was 

 considerable difficulty in getting the needle through the intervals between 

 the laminae. Puncture for the purpose of inducing spinal anaesthesia is by 

 nearly all surgeons practised in the middle line. This necessitates going 

 through the three ligaments, Supraspinous, Interspinous and Lig. Subflavium, 

 the latter two of which typically consist of two lateral sheets with looser 

 tissue between. The needle has to be guided forwards and very slightly 

 upwards between the margins of the adjacent spinous processes, which are 



