1889. ] THE BODY-CAVITY IN LIZARDS, ETC. 459 
from spinal nerves ; while the nerves that supply the muscle in the 
antero-dorsal region of the “oblique septum’ seem comparable to 
parts of the sympathetic of Mammals, in which group the diaphragm 
is partly supplied from the solar plexus *. 
Uskow (5, p. 214), in giving a résumé of the different types of 
diaphragm, says that the condition in Man is like that in the Rabbit, 
except that a part of the diaphragm is fused with the pericardium ; 
and that the diaphragm of the Fowl is the same as that in Man, but 
the diaphragm has no muscle, and its ventral portion is entirely 
fused with the substance of the pericardinm. 
I do not, however, think, in the light of the clear description he 
gives elsewhere of the important differences between the mammal 
and bird, in the regions of the diaphragm (see below p. 462), that 
such remarks are necessarily to be taken as implying a belief in an 
approximate morphological homology. 
Huxley, on the other hand (4, p. 567), says “neither in Apteryx 
nor in any other bird has either of these [pulmonary aponeurosis 
and oblique septum] the slightest real resemblance to a Mam- 
malian diaphragm. For, as has been seen, the heart lies altogether 
behind both, and the muscular digitations of the pulmonary 
aponeurosis are supplied by the intercostal nerves, the phrenic being 
absent. The vertical and oblique septa” really answer to the fibrous 
tissue of the posterior and middle mediastinum in Mammals. In 
this, as in all other cases, the meaning of ornithic peculiarities of 
structure is to be sought, not in Mammals but in Reptiles.” And 
he goes on to mention certain avian characteristics which are 
elsewhere only represented in Reptiles, and to compare the Crocodile 
with the Bird. 
Huxley’s verdict on the question of the diaphragm, as thus 
tersely stated, failed to remove the suspicion that while the more 
central part of the avian diaphragm doubtless corresponded to 
mediastinal tissue, a considerable portion thereof, more lateral in 
position, might be homologous with the diaphragm of Mammals. 
And it was only after reading Ravn’s paper (9), in which, pp. 139- 
147, he goes at some length into the development of what His 
1 A rather similar line of reasoning occurred to the writer independently. 
For instance, in investigating the nature of the nerve-supply, the question at 
once presented itsel{—Where is one to look for the homologue of the phrenic 
nerve? What is the phrenic nerve? In Mammals it appears as a specialized 
trunk (supplying a specialized muscle), composed of factors from a rather in- 
definite number of spinal neryes of the cervical region. But seeing that there 
is this indefiniteness, and that the division into regions (thoracic, cervical, &e., 
&e.) of the vertebral column in Birds and Mammals is so very different, a 
definite answer was not reached. I was rather inclined, however, to regard as 
possibly to be reckoned in the same series with the phrenic nerve, those nerves 
which are connected with the spinal nerves in the thoracic region (of the Duck) 
rather after the manner of the sympathetic, and which, I presume, are the 
nerves referred to by Sappey, in his second category, as supplying fibres to the 
‘oblique septum.” In spirit-specimens, however, I did uot detect any nerve- 
fibres passing from them to that structure. 
2 It will be noticed that he does not refer to the pulmonary aponeurosis 
with the oblique septum as homologous with the mediastinal tissues. 
ol 
