52 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
dorsal surfaces of two similar processes, prezygapophyses, borne on 
the anterior border of the next vertebra posterior. Laterally the 
neural arch is a thin plate, except at its middle third, from which 
the heavy transverse process, arising partly from it and partly from 
the centrum, projects in a postero-lateral direction. The transverse 
process is made up of two portions, one dorsal and one ventral, 
each of which articulates distally with the corresponding head of 
the proximally-forked rib. 
The vertebrae are principally bony, the cartilaginous parts being 
few and hardly distinguishable from the bony ones. 
The first vertebra bears no rib and is otherwise modified from the 
Fig. B.—Posterior caudal vertebrae, lateral view, x 12. H. S., haemal spine; N. S., 
neural spine. 
typical form. It bears three anterior processes, one median and two 
lateral, all of which articulate with the skull (odontoid vertebra of 
W. K. Parker). The median process has a flat, cartilaginous tip, 
partially encased in bone, which lies dorsal to the basi-occipital arch 
and is attached to it laterally. 
Posterior to this, it becomes 
thicker and broader and is bony, 
not cartilaginous, finally joining 
with the two lateral processes to 
form the body of the first verte¬ 
bra. The two lateral processes 
also have cartilaginous tips, en¬ 
cased in bone, which articulate 
with the occipital condyles. 
The body of the first vertebra is anteriorly very broad but narrows 
rapidly and assumes the hour-glass form. The neural arch is very 
broad anteriorly, its anterior border being slightly posterior to the 
joining of the anterior processes to form the body. The transverse 
process is much less developed than in the other trunk vertebrae. 
The sacral vertebra does not differ from the typical form, but the 
caudal vertebrae are much modified. 
Fig. C.— Attachment of pelvic girdle. 
X 12. Fe., femur; II., Ilium; Pub., 
pubo-ischium. 
