The spinal cord extends from the foramen magnum to the lower border of the first lumbar vertebra(transpyloric plane). (Fig. VII, 5., Fig. XVII, 2.)
The cord follows the curves of the vertebral column, and presents also two enlargements, the intumescentia cervicalis and lumbalis. The former swelling lies between the third cervical and second dorsal vertebrae, the latter between the ninth and twelfth dorsal vertebrae. Near its termination the cord tapers away as the conus medullaris. The filum terminale, the prolongation of the cord, is continued onwards from the lower part of the body of the first lumbar vertebra to near the tip of the coccyx, (Fig. VII, 7., Fig. XVII, 3.) at which level it blends with the periosteum lining that bone.
The theca vertebralis, or dural sheath, extends as low as the third sacral vertebra,(Fig. VII, 6., Fig. XVII, 1.) at which level it is pierced by the filum terminale.
A line uniting the two posterior superior iliac spines cuts across the second sacral spine, (Fig. VII, 10., Fig. XVII, 15.) and the dural sac, therefore, terminates about 1/2 inch below the level of this interspinous line. At the third month of intra-uterine life the cord extends the whole length of the vertebral canal, whilst at birth it reaches as low down as the third lumbar vertebra.
A reference to Fig 7 will show that cerebro-spinal fluid might be withdrawn from the thecal canal anywhere between the termination of the cord at the level of the transpyloric plane and the base of the sacrum. A line drawn across the back, at right angles to the long axis of the body, at the level of the highest part of the iliac crests, cuts across the median posterior line at the level of the interspace between the laminae of the second and third or third and fourth vertebrae. It is at this point, or rather to one side of this point, that lumbar puncture is carried out.
A brief account only will be given, as, though the landmarks are most important, the tendency is great to drift into the question of surgical applied anatomy, a pitfall which the writer is most anxious to avoid.
The perineum is, in shape, roughly quadrilateral, the lateral boundaries being formed in front by the diverging rami of the pubis and ischium, and behind by the ischial tuberosity and the gluteus maximus muscle. The anterior and posterior angles of the space are formed respectively by the symphysis pubis and the tip of the coccyx. The subpubic angle is obtuse in the female and acute in the male. In the female, also, the ischial tuberosities are further apart and slightly everted. The perineum is divided into two areas by a line drawn between the anterior part of the ischial tuberosities, thus forming
(a) The genital area.
(b) The rectal area.
This transverse line passes about 1 inch in front of the anus, and represents the level of the two transverse perinei muscles, the posterior border of the triangular ligament, and the line along which Colles's fascia is reflected round the posterior border of the two transverse perinei muscles to become continuous with the posterior border of the triangular ligament. The "central tendinous point of the perineum" corresponds to the middle of this line, and forms the point of attachment of several muscles.