* 
ON THE VERTEBRATE SKELETON. 267 
broad pleurapophyses are occasionally ossified from two centres in the great 
land-tortoises of India and the Galapagos isles. The free extremities of the 
short cervical pleurapophyses of crocodiles and plesiosaurs are expanded and 
produced forwards and backwards, like axe-blades, whence the name of 
‘hatchet-bones,’ applied to them prior to the recognition of their true homo- 
logy. 
"The pleurapophyses are appended sometimes simply to the ends of par- 
apophyses ; sometimes to the ends of diapophyses; sometimes by a head and 
tubercle to both kinds of transverse processes ; sometimes directly to the 
side of the centrum; and sometimes they are shifted backwards over the in- 
tervertebral space, and are articulated equally to two centrums (human 
thorax), and sometimes to two centrums, to a neurapophysis and to a long 
diapophysis, as in the sacrum of the ostrich (fig. 27, pl). In the atlas of 
some fishes the pleurapophysis is detached from its centrum, and is suspended, 
with its heemapophysis, from the antecedent hzemal arch (scapulo-coracoid). 
In some sturgeons the abdominal pleurapophyses are composed of two or 
more cartilaginous pieces. I have observed some of the expanded pleurapo- 
physes in the great Testudo elephantopus ossified from two centres, and the 
resulting divisions continuing distinct but united by suture. The pelvic 
pleurapophysis is in two pieces, as a general rule (fig. 28, pl’ attached to 
D"); and the lower piece is the seat of that most common and simple kind 
of modification, viz. increase of size with change of form from the cylindrical 
to a flat bone (as indicated by the dotted line in fig. 27), whereby it comes 
into connection with the pleurapophyses of other vertebre besides the proxi- 
mal piece of its own; such pleurapophyses having their development stunted 
so as not to exceed in size the proximal portion of the pelvic pleurapophysis, 
whose expanded distal portion (62) receives the special name of ‘ilium.’ This 
bone retains its rib-like shape however in the chelonians, as in the batrachians: 
in most species it unites below with two hzmapophyses, called, on account 
of their modifications of form and proportions, ‘ischium’ and ‘ pubis.’ The 
pleurapophyses defend the hzmal or visceral cavity ; they are the fulcra of 
the moving powers which expand and contract such cavity in respiration, 
when its walls admit of those movements ; they frequently support ‘ diverging 
appendages,’ and give origin to muscles moving such appendages, or acting 
upon the vertebral column. In some exceptional cases the pleurapophyses 
become, themselves, locomotive organs, as in serpents and the Draco volans. 
The hemapophyses, as osseous elements of a vertebra, are less constant than 
the pleurapophyses ; although they sometimes exist in segments, e. g. the 
lumbar vertebra of certain saurians, and in the case of the ischium, or second 
“pelvic heemapophysis, in which the corresponding pleurapophyses are absent, 
or short, or anchylosed to the transverse processes. The only true bony 
hzmapophyses in the trunk of fishes appear to be those of the atlas, forming 
the lower piece of the epicoracoid ; and of the last (?) abdominal vertebra, 
forming the ischial or pubic inverted arch supporting the appendages called 
‘ventral fins.’ It is at least to the last abdominal vertebra solely that the 
homologous arch and appendages are connected, by the medium of the 
pleurapophyses (iliac bones) in the batrachians, and it needs but the removal 
of the pleurapophysis, or of its second complementary portion (pl! in fig. 
*28), to reduce that vertebral segment to the condition which it presents in an 
abdorainal fish. The so liberated inferior (hemapophysial) portion of the 
pelvic (last abdominal costal) arch is subject, in fishes, to changes of pesition 
far more extensive than have been observed in the neurapophyses or pleur- 
apophyses of the trunk-vertebra, without however preventing the recognition 
of the segment to which such shifted hemapophyses actually and essentially 
oe G Wa? 
