No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 439 
that the fluid should find its way along this channel first, and 
then extend into the body cavity from this point, giving pic- 
tures which in transverse section are like Fig. 40. Surface 
views could not decide that these cavities communicate freely ; 
and these sections which I have studied were no doubt made 
after Budge had written the rough draft of his manuscript, as 
they are not referred to in his paper. 
Although the body cavity of the bird is formed after the 
same manner as it is in the human embryo, there is one marked 
difference in the formation of the pericardial space. In the 
bird the mesoderm does not extend throughout the head fold 
of the blastoderm, leaving a portion of the ectoderm in direct 
contact with the entoderm. Later the mesoderm grows into 
this region, and at the same time the pericardial cavity extends 
to the outside of the body. This condition continues for a long 
time, allowing the pericardial cavity to communicate with the 
false amnion after the embryo is well formed. Duval’s excel- 
lent Atlas shows how the pericardial cavity first communicates 
with the exterior of the body, and after the body walls have 
united the heart still lies in apposition with the liver, as there is 
no septum transversum. The only trace of a septum trans- 
versum that I can find in young chicks is at the point the 
Cuvierian ducts enter the heart. Here a bridge of tissue passes 
transversely to the body. The liver does not grow into it, but 
accompanies the single omphalomesenteric vein before it enters 
the heart? 
Development of the Diaphragm.— Our knowledge of the 
development of the diaphragm is based upon the researches of 
von Baer,? Cadiat,? His,t Uskow,® and Ravn.6 Each contrib- 
uted his portion: von Baer that the diaphragm is at first 
located high in the neck and must descend in its development, 
and, because of its high position at first, is innervated by a 
1 Since the above has been written this subject has been studied thoroughly 
by Ravn, whose paper will be found in His’s Archiv, 1896. 
2 Von Baer: Entwicklungsgeschichte, 1837. 
8 Cadiat: Jour. de l’Anat. et de la Physiol., 1878. 
4 His: Anat. mensch. Embryonen, Th. I, 1880. 
5 Uskow: Arch. f. mik. Anat., 1883. 
® Ravn: His’s Archiv, 1889. 
