40 THE SKELETON OF THE HORSE 
is thick, the lateral part thinner, narrower, and curved forward. The medial part 
of the fifth is also somewhat thickened. Medial to the articular surfaces the edges 
of the transverse processes are cut into by notches, which form foramina by apposi- 
tion with each other and the sacrum. 
The spinous processes resemble those of the last two thoracic vertebrie. 
wae 
Spinous process 
~ Mammillary process 
A 
rticular process 
Transve Tse pracess 
Notch See a 
Vertebral foramen 
Body 
Ventral spine 
Fic. 16.—Seconp LumMBar VERTEBRA OF Horse; Posterior View. 
They are usually about equal in height, but minor differences are common, and the 
width diminishes in the last three. 
Development.—This is similar to that of the thoracic vertebra. The extremi- 
ties of the transverse processes remain cartilaginous for some time after ossification 
is otherwise complete. 
The transverse processes of this region are considered equivalent to the proper transverse 
process + the costal element, and hence the distinctive term processus lateralis (s. costarius) 
CO . ~ 
Spinous process 
Vertebral foramen 
} Articular processes 
m, 
Transverse process 
Notch Body Articular surface for 
wing of sacrum 
Fic. 17.—Last Lumpar VertTeBRA OF Horse; Posterior VIEW. 
has been proposed. The occurrence of a rib in connection with the transverse process of the first 
lumbar vertebra is common. Reduction of the number to five has been observed frequently, and 
may or may not be compensated by an additional thoracic vertebra. Very few cases are recorded 
of seven lumbar vertebra—especially with the normal thoracic number. An anomalous vertebra 
with mixed thoracic and lumbar characters sometimes occurs at the junction of the two regions. 
