_septum
transversum_, and in this the central tendon is formed. The fleshy
portion is developed on each side in two parts, an anterior or
sterno-costal which is derived from the longitudinal neck musculature,
probably the same layer from which the sternothyroid comes, and a
spinal part which is a derivative of the transversalis sheet of the
trunk. Between these two parts is at one time a gap, the _spino-costal
hiatus_, and this is obliterated by the growth of the
pleuro-peritoneal membrane, which may occasionally fail to close and
so may form the site of a phrenic hernia. With the growth of the body
and the development of the lungs the diaphragm shifts its position
until it becomes the septum between the thoracic and abdominal
cavities. (See A. Keith, "On the Development of the Diaphragm," _Jour.
of Anat. and Phys._ vol. 39.) A. Paterson has recorded cases in which
the left half of the diaphragm is wanting (_Proceedings_ of the
Anatomical Society of Gt. Britain, June 1900; _Jour. of Anat. and
Phys._ vol. 34), and occasionally deficiencies are found elsewhere,
especially in the sternal portion. For further details see Quain's
_Anatomy_, vol. i. (London, 1908).

_Comparative Anatomy._--A complete diaphragm, separating the thoracic
from the abdominal parts of the coelom, is characteristic of the
Mammalia; it usually has the human structure and relations except that
below the Anthropoids it is separated from the pericardium by the
azygous lobe of the lung. In some Mammals, e.g. Echidna and Phocoena,
it is entirely muscular. In the Cetacea it is remarkable for its
obliquity; its vertebral attachment is much nearer the tail than its
sternal or ventral one; this allows a much larger lung space in the
dorsal than in the ventral part of the thorax, and may be concerned
with the equipoise of the animal. (Otto Muller, "Untersuchungen uber
die Veranderung, welche die Respirationsorgane der Saugetiere durch
die Anpassung an das Leben im Wasser erlitten haben," _Jen. Zeitschr.
f. Naturwiss._, 1898, p. 93.) In the Ungulata only one crus is found
(Windle and Parsons, "Muscles of the Ungulata," _Proc. Zool. Soc._,
1903, p. 287). Below the Mammals incomplete partitions between the
pleural and peritoneal cavities are found in Chelonians, Crocodiles
and Birds, and also in Amphibians (Xenopus and Pipa). (F. G. P.)

DIARBEKR[1] (_Kara Amid_ or Black Amid; the Ro