Occasionally the laminæ do not form completely and the membranes of the cord may bulge out and form a tumor, or the cord itself may come out also. This generally occurs in the lumbar region, where it is known as _spina bifida_. If in case of fracture of a vertebra there is paralysis of the parts below due simply to the pressure of a fragment of bone upon the cord, it may be completely cured by removal of the fragment. If, however, the cord suffers injury, the paralysis will remain. _Humpback_ or _Pott’s disease_ is caused by the tubercle bacillus, which eats away the bodies of the vertebræ so that the column caves in and the spinous processes are thrown out in a hump or kyphos. [Illustration: FIG. 34.--Muscles of the right side of the head and neck: 1, Frontalis; 2, superior auricular; 3, posterior auricular; 4, orbicularis palpebrarum; 5, pyramidalis nasi; 6, compressor naris; 7, levator labii superioris alæque nasi; 8, levator labii superioris; 9, zygomaticus major; 10, orbicularis oris; 11, depressor labii inferioris; 12, depressor anguli oris; 13, anterior belly of digastric; 14, mylohyoid; 15, hyoglossus; 16, stylohyoid; 17, posterior belly of digastric; 18, the masseter; 19, sternohyoid; 20, anterior belly of omohyoid; 21, thyrohyoid; 22, 23, lower and middle constrictors of pharynx; 24, sternomastoid; 25, 26, splenius; 27, levator scapulæ; 28, anterior scalenus; 29, posterior belly of omohyoid; 30, middle and posterior scalenus; 31, trapezius. (Dorland’s Dictionary.)]