G PROCEEDINGS OF THE ANATOMICAL AND ANTHROPOLOGICAL 



The relation of the lumbar spinous process to the body of the vertebra 

 is such that, when the latter is placed horizontally, the upper margin of the 

 spine is at the level of the horizontal plane through the middle of the body, 

 and the lower margin about in. lower than the under surface of the body. 

 The 5th spine is often altogether below the level of the body. It is to be 

 noted, however, that the lumbar spinous processes are practically horizontal, 

 at least in the lower ones, bee vuse of the oblique position of the body of 

 the vertebra. 



The interval between the neural arches of two adjoining lumbar vertebrae 

 is a somewhat triangular opening with the base below, the apex pointing 

 upwards and backwards, and the angles rounded. It is bounded externally 

 by the inferior articular processes of the upper vertebra and the lower margin 

 of the laminae running from these articular processes upwards, inwards and 

 backwards to meet in the base of the spinous process of the same vertebra. 

 The plane of this boundary therefore runs downwards and forwards, making 

 an angle of about 45 with the vertical and the horizontal. The lower 

 boundary or base of the triangle is formed by the upper margin of the 

 laminae of the vertebra below. To one looking from behind, this boundary 

 usually appears as one straight line, but it really consists of two lines running 

 inwards and somewhat backwards to meet in the base of the spinous process, 

 i.e., two lines meeting at a very wide angle but lying in a horizontal plane. 

 Sometimes the plane is not horizontal, when the middle of the lower boundary 

 is, at a higher level than the two extremities and so encroaches on the interval 

 between the laminae, giving a somewhat kidney-shaped opening. The lower 

 boundary lies deeper from the surface than the upper one owing to the fact 

 that the lamina, especially in the lower two or three vertebras, slopes from its 

 upper to its lower border down and back at an angle of about 45 to the vertical. 

 Hence an exploring needle would strike the upper boundary of the space at 

 a depth of about 1 in. from the level of the tip of the spinous process, whereas 

 the lower boundary is about | in. deeper. It follows from this that in punctur- 

 ing outside the middle line, one gets the widest interval by directing the needle 

 .somewhat upwards as well as forwards and inwards. 



.As regards the actual size of the interval, this varies with the flexion and 

 extension of the spine. In full extension the spinous processes practically 

 touch each other. Flexion is the freest movement in the lumbar region, 



