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humerus in the Apteryx, the true muscles of the back, which correspond to the second
layer of the dorsal muscles in Man, become immediately visible on removing the dorsal
integuments and fasciae ; they consist of the sacro-lumbalis, longissimus dorsi, and spinalis
dorsi. The first two muscles are blended together at their posterior origins, but soon
assume the disposition characteristic of each as they advance forwards.

The sacro--lumbalis (Pl. XI. XII. l) is a strong and fleshy muscle, six lines in breadth,
and three or four lines in thickness : it is, as usual, the most external or lateral of the
muscles of the back, and extends from the anterior border of the ilium to the penulti-
mate cervical vertebra. Origin. By short tendinous and carneous fibres from the outer
half of the anterior margin of the ilium, and by a succession of long, strong, and flat-
tened tendons (Pl. XII. l 1-l 5) from the angles of the fifth and fourth ribs, and from
the extremities of the transverse processes of the third, second, and first dorsal vertebrae ;
also by a shorter tendon ( l 6) from the transverse process of the last cervical vertebra ;
these latter origins represent the musculi accessorii ad sacro-lumbalem ; to bring them
into view, the external margin of the sacro-lumbalis must be raised, as in Pl. XII.fig. 2.
These accessory tendons run obliquely forward, expanding as they proceed, and are lost
in the under surface of the muscle.

Insertion. By a fleshy fasciculus with very short tendinous fibres into the angle of the
sixth rib, and by a series of corresponding fasciculi, which become progressively longer
and more tendinous into the angles of the fifth, fourth, third and second ribs (Pl. XI. l*),
and into the lower transverse processes of the first dorsal and last two cervical vertebrae :
the last insertion is fleshy and strong ; the four anterior of these insertions are concealed
by the upper and outer fleshy portions of the sacro-lumbalis, which divides into five elon-
gated fleshy bundles (Pl. XI. l **), inserted successively into the upper transverse pro-
cesses of the first three dorsal and last two cervical vertebrae. These last insertions
seem to represent the continuation of the sacro-lumbalis in Man, which is termed the
cervicalis descendens or ascendens.

Longissimus dorsi (PL. XI. XII. m). - This muscle is blended posteriorly both with the
sacro-lumbalis and the multifus spinoe, and anteriorly with the outer portion of the
spinalis dorsi. It extends as far forward as the thirteenth cervical vertebrae. Origin.
From the inner or mesial half of the anterior margin of the ilium ; from a strong apo-
neurosis attached to the spines of the eigth, seventh and sixth dorsal vertebrae ; and from
the transverse processes of the sixth, fifth, fourth and third dorsal vertebrae. Ins. The
carneous fibres continued from the second origin, or series of origins from the spinous
processes, incline slightly outward as they pass forward, and are inserted into the poste-
rior articular processes of the first three dorsal vertebrae, receiving accessory fibres from
the spinalis dorsi. The fasciculi from the transverse processes incline inwards, and are
also inserted into the posterior oblique processes of the vertebrae anterior to them ; they
receive fibres from the iliac origin, and soon begin to form a series of oblique carneous
fasciculi, which become more distinct as they are situated more anteriorly ; they are at