328 _ REPORT—1846. 7 
? 
The special homologies of these elements of the pelvis being thus deter- 
mined, it follows, that their general homology, as ‘it may be revealed by the 
simple condition of the pelvic arch in the species in which the pelvis, as 
complete and fixed to a sacrum, makes its first appearance in the animal 
kingdom, will be equally applicable to the parts under all their metamor- 
phoses in the higher air-breathing vertebrates. 
The correspondence of the segment of the endoskeleton in the menopome 
D’, Pl’, H, A, with the typical vertebra, as illustrated by fig. 15, is such, 
that any other explanation of its essential nature than as a representative or 
repetition of such fully developed segment or vertebra seems contrary to ~ 
nature. The chief modification has its seat in the most peripheral part or 
appendage A. as compared with its simple homologue in the thoracic segment 
of the bird (fig. 15). If 62 and 61 are to be regarded as strangers to the 
vertebral system, new parts introduced for special purposes, and not as 
normal elements modified for special purposes, I am at a loss to know on 
what principles, or by what series of comparisons we can ever hope to attain 
to the higher generalizations of anatomy, or discover the pattern according 
to which the vertebrate forms have been constructed. It may be said thatthe 
arch which they constitute performs a new function, inasmuch as it sustains 
a locomotive limb which reacts upon the ground. But this new function 
arises in the menopome, rather out of the modifications of the appendage 
than of the arch itself. In so far as the mere support of the appendage is 
concerned, the inverted or hemal arch Pl’, H, performs no new function, but 
one which is common to such arches inthe thorax of birds, and to the less com- 
pletely ossified homologous arches in the abdomen of fishes, where moreover 
the simple diverging appendages do give attachment to the muscles of locomo- 
tion. Comparing, then, the hemal arch in question with that of the typical 
vertebra (fig. 15), we find that, like the scapulo-coracoid arch in fishes 
(fig. 5, H 1), its parts are open to two interpretations. The upper piece of 
Pl' may be thewhole pleurapophysis, the lower, 62, the heemapophysis, and the 
part, 64, the half of an expanded and bifid hemal spine: or Pl’ with 62, may 
be two portions of a teleologically compound pleurapophysis, and 64 the heem- 
apophysis, which would join with its fellow without, or with a mere rudiment 
of, a hemal spine intervening. From the analogy of the scapulo-coracoid 
arch in fishes, which is proved by its modifications in higher animals to 
want the hemal spine, it is most probable that such is the condition and 
true interpretation of the correspondingly simple pelvic arch under considera- 
tion. But the genera] relation of this arch to the hemal one of the typical 
segment is not affected by the alternative. ~ 
I regard, therefore, Pl’, 62, as two portions of a fully developed pleurapophy-- 
sis; and the pleurapophyses, Pl’, P/ of the contiguous vertebree as answering 
only to the upper portion of the pelvic one. In ascending from the meno- 
pome to the crocodile, we find the homologue of 62 broader than it is long, 
and articulated to the thickened proximal portions of the pleurapophyses of 
two segments ; and we observe, likewise, the pelvic arch completed below 
by two pairs of hemapophyses: for the anterior pair the name of ‘ossa 
pubis’ is retained ; to the posterior pair that of ‘ischia’ is given. In general 
homology these bones complete, as hemapophyses, the two vertebral seg- 
ments modified to form the sacrum of the crocodile; and the intermediate 
connecting piece (ilium) may be interpreted, as either the confluent distal 
portions of the pleurapophyses of both vertebree, or as an expansion of one 
such portion, answering to 62 in the menopome, and intruding itself between 
the stunted pleurapophysis and distant hemapophysis of the second sacral 
vertebre in the crocodile. 
Saag 
