268 REPORT—1846. 
belong. The homologous hzmal arch exists in the same free and detached 
condition in cetaceans and enaliosaurs ; but in all other air-breathing verte- 
brates it is connected with the iliac bones and completes the typical character 
of the proper sacral vertebra. The bony hemapophyses of the lumbar vertebrae 
are found suspended in the fleshy abdominal walls of certain saurians: but in 
the region of the thorax in these and higher vertebrates, the heemapophysis 
(fig 15, h) articulates by one end to the pleurapophysis (pl) and by the 
other to the hzemal spine (sternal bone, fs) ; or its lower end is attached to a 
contiguous hemapophysis ; or it is suspended freely from the pleurapophyses 
(as in the ‘ floating ribs» of man and mammals), or it may be joined below 
to the sternum, and have its upper end free, as in the seventh dorsal vertebra 
of the Ciconia Argala. When the upper end of the hemapophysis articulates 
with the pleurapophysis in birds, it is usually by a distinct condyloid joint, 
with smooth articular cartilage and a synovial capsule. 
Where hemapophyses exist in the tail, they articulate directly to the 
under part of the centrum, or to two centrums at the intervertebral space ; 
and are either free at the opposite end, as in some caudal vertebre of ser- 
pents and in those of the enaliosaurs, or they are confluent with each other 
at their distal ends; when each pair of hemapophyses forms the so-called 
V-shaped or chevron-bone. The changes of position of that detached ‘ pubic 
arch’ or ‘chevron-bone’ which supports the ventral fins in fishes afforded 
Linnzeus the characters of the orders ‘ Abdominales,’ ‘ Thoracici,’ and 
‘Jugulares’ in the ‘ Systema Naturz’; and its immortal author, in giving the 
name ‘ Apodes’ to those fishes in which the ventral fins were absent, con- 
cisely indicates his perception of their relation to the hind-legs of batrachia 
and the lower limbs of man. If, then, mere change of relative position, 
however extensive, failed to conceal the special homology of the detached por- 
tion of the pelvic arch and its appendages from the keen-sighted naturalist, 
still less ought such a character to blind the philosophic anatomist to the 
general homology of such detached vertebral elements, or prevent his tracing 
them, wherever he may find them, to the remainder of their proper segment; 
especially when its place is so clearly and beautifully indicated, as it is by the 
condition of the pelvic arch in the perennibranchiate reptiles (fig. 28). 
The function of the hemapophyses is to complete, with or without a hemal 
spine, the hemal arch of the vertebral segment ; and, in so far to protect the 
hzemal or visceral cavities and support their contents. They give attachment 
to the lower or ventral portions of the primary muscular segments ‘myo- 
commata’*, called ‘intercostals’ in the thorax, and ‘recti abdominis’ in the 
abdomen of the higher vertebrata; and they thus serve as fulcra to the 
muscles that expand and contract the abdominal or thoracic-abdominal cavity : 
and sometimes more directly aid in these movements by the elasticity resulting 
from an arrest in their histological development at the cartilaginous stage, e.g. 
in the thorax of most mammals. Hzmapophyses may support or aid in sup- 
porting diverging appendages; and in giving attachment to the muscles of 
those appendages. The hemapophyses are usually slender, longer, or shorter 
simple bones; but are broad and flat, overlapping each other in the thorax 
of monotremes: they become broader and shorter in the expanded and fixed 
thoracic abdominal bony case of chelonians, and are still broader where they 
close the pelvic arch in the plesiosaurs. Inthe abdominal region of these ex-* 
tinct saurians and in crocodiles, the freely suspended heemapophyses are com- 
pounded of two or more overlapping bony pieces. 
* See the description of these segments, usually confounded under the name of the ‘ great 
lateral muscle’ or ‘ longitudinal muscles’ in fishes.—Hunterian Lectures on Vertebrata, 8vo, 
pp. 163-165. 
