114 MAMMALIAN ANATOMY 



VENTRAL ASPECT. 



The ventral aspect of the vertebral column is less complicated than 

 either the dorsal or the lateral aspect ; it is merely a long strip formed 

 of the ventral surfaces of the vertebral bodies and the ventral edges 

 of their uniting intervertebral disks, and prolonged at each side at 

 intervals on the ventral surface of the transverse processes. 



The ventral surface of the column begins wide and flat at the atlas, 

 where the wing-like transverse processes are only slightly dorsal to the 

 ventral arch. It is abruptly narrowed at the axis, whereof the trans- 

 verse processes contribute little to its formation. It then widens to the 

 fifth cervical, where it begins to narrow again slightly to the seventh. 

 In this region, from the second to the seventh cervical, the ventrally 

 directed costal elements of the transverse processes convert the ventral 

 aspect of the neck into a wide but deep channel, which lodges the 

 ventral cervical flexor muscles. In the seventh cervical and the first 

 thoracic vertebra the bodies are flattened and almost continuous at 

 each side with the transverse processes, but as we proceed toward the 

 tail we observe that the bodies become more convex transversely and 

 the transverse processes rise higher on the pedicles, until they dis- 

 appear on the eleventh thoracic vertebra. Here the vertebral body 

 begins to assume the transversely flattened form it retains for the rest 

 of the thoracic and throughout the lumbar region. At the first 

 lumbar the transverse processes appear again on a level with the 

 ventral surface of the bodies, and are directed ventrally toward the 

 head and laterally, again converting the ventral aspect into a muscular 

 channel, which is continued on the cephalic end of the sacrum. In 

 the caudal part of the sacrum and in the tail there is no such median 

 channel, and the surface of the body and the surface of the transverse 

 processes lie almost in the same plane, with the bodies somewhat convex 

 transversely. In the region of the tail the transverse processes have a 

 caudal and lateral direction as far as the sixth or seventh vertebra, 

 where the cephalic transverse processes begin. 



The middle line of the ventral aspect of the vertebral column, in 

 the cervical and lumbar region, is raised into a longitudinal keel, and, 

 in the tail, tubercles at the cephalic end of each body support the 

 chevron bones. Since each vertebral body is more or less concave 

 in a cephalo-caudal line, the column, as a whole, is alternately concave 

 and convex in this direction. 



