118 
ORIGINAL ARTICLES. 
the dorsal transverse processes. The outermost tubercle on the 12th 
dorsal vertebra, although not furnished with a cartilaginous facet like 
the processes above it, is closely attached to the rib by ligamentous 
union; and where a 13th rib is present, this rib is similarly connected 
with the transverse process of the first lumbar vertebra. This con¬ 
nection is beautifully exhibited in a series of specimens collected by 
Professor Thomson, and used by him in illustrating his lectures. In 
one specimen, a short rib is anchylosed to the front of the left trans¬ 
verse process of the first lumbar vertebra, and has no other point of 
contact with the vertebral column; and in others there is a similar 
disposition without anchylosis. Thus the transverse processes of the 
lumbar vertebrae correspond to the parts of the dorsal transverse 
processes which support the ribs; and, being longer, to a certain extent 
they take up the functions of their prolongations the ribs themselves, 
for the external row of intertransverse muscles in the lumbar region 
are in series with the levatores costarum of the thorax, while the 
internal row of lumbar intertransverse muscles, passing from mam¬ 
millary to mammillary process, are in series with the intertransverse 
muscles of the thorax. # 
I have thus dwelt on those manifest relations of the dorsal trans¬ 
verse process to the lumbar processes, because they lead to important 
general conclusions. They show that a process in one segment may 
be serial with more than one process in another segment, or, in other 
words, may become expanded in another segment into several pro¬ 
cesses. To put the matter more generally: structures which lie 
in series are not necessarily morphologically identical. Thus the 
mere suppression of the lumbar transverse and accessory processes 
would not render the mammillary processes complete representatives 
of the dorsal transverse processes; and hence we are prepared to 
meet with series in which the anterior members of the series have a 
different morphological value from the posterior members. 
Let us now very shortly recount the principal facts with regard 
to the disposition of ribs and vertebral processes in. different animals, 
and some of the theories which have been brought forward to ex¬ 
plain them. 
In mammals, birds, and reptiles the transverse process in the 
trunk arises in common with the neural arch, and is in serial con¬ 
nexion with processes in the tail which strike out transversely and 
are completely separated from the inferior arches frequently found in 
that region. Between the transverse and spinous processes other 
processes may appear; viz. the mammillary and accessory processes, 
which may become merged in the transverse processes. 
Bibs tending to surround the visceral cavity are in the majority 
of cases articulated both to the tips of the transverse processes and to 
points close to the bodies of the vertebrae, variable in their exact 
* This is noticed by Muller, Yergl. Anat. der Myxinoiden, p. 245. 
