aHantal foramen 



prezygapophysis (articular surface) spine 



articular surface 



neural spine 

 transverse process 



transverse canal 

 A ATLAS 



neural spine 



■ I neural canal 



transverse canal 



postzygopopliysis 



B AXIS 



prezygapophysis (articular surface) 

 postzygapophysis / ^„-_,^^spine 



postzygapophysis 



C 3rd CERVICAL 



nsverse process 



transverse process 



diapophysis 

 parapophysis 



D 5th THORACIC g 2rd LUMBAR 



Figure 6-1. Some of the vertebrae of the cat as seen in anterolateral ond slightly dorsol view 



ntercentral haemal arch 

 F MIDDLE CAUDAL 



bral construction. In the case of the mammal, the body is 

 usually formed from the centrum (and its epiphyses); there- 

 fore, the terms can be interchanged, although the former 

 term is less ambiguous. In some animals (or individual 

 vertebrae — see account of axis below) the body is not 

 formed entirely from the centrum; it includes the intercen- 

 trum. In other animals the body may be largely intercentral 

 in origin or it might not be known whether centrum, inter- 

 centrum, or both, are involved. In these situations, body 

 and centrum are not synonyms. 



Anteriorly the base of the neural arch and the body of 

 the axis have broad, somewhat laterally directed articular 

 surfaces for the atlas. Between these surfaces is the finger- 

 like odontoid process. The transverse process is small, pos- 

 terolaterally directed, and perforated at its base by the 

 vertebral foramen. 



In the young animal, six ossification centers are apparent; 

 bilateral neural arches meeting dorsally to form the crest or 

 spine and forming the postzygapophyses, the transverse 

 processes, and most of the atlas articular pads; and four 

 midline bones forming the body, which, from behind for- 

 ward, are the epiphysis, centrum, and intercentrum of this 

 vertebral segment, and the centrum of the atlas forming the 

 odontoid process. The articular surface for the atlas involves 

 both the atlas centrum and the base of the neural arches of 

 the axis. The anterior tip of the odontoid process may also 

 include the centrum of a pro-altas vertebra. 



The third cervical is like the rest of the cervicals in hav- 

 ing a dorsal spine, both pre- and postzygapophyses on the 

 neural arch, and transverse processes drawn out and back. 



each with a vertebral foramen through its base (the foramen 

 is lacking in the seventh cervical of the cat and in many other 

 animals). The anterior margin of the transverse process is 

 drawn out forward and medially so as to lap inside the pos- 

 terior end of the transverse process of the axis. This over- 

 lapping is better marked in the opossum and is related to 

 muscle attachment rather than articulation of vertebrae. 

 The seventh cervical lacks the forward extension of the trans- 

 verse process and, in the cat, only the dorsal root of the proc- 

 ess is present. 



In the young animal, each cervical arises from five ossifi- 

 cations: there is a pair of neural arches, which meet dorsally, 

 extend upward as a dorsal spine (particularly evident in the 

 opossum), and basally form the transverse processes; and 

 below them is the centrum, with its separate anterior and 

 posterior epiphyses. 



The thoracic vertebrae have tall neural spines with pre- 

 and postzygapophyses lateral to the neural canal. The 

 transverse process of either side has a single root above the 

 vertebral artery and distally has an articular facet for the 

 dorsal head of the rib, the diapophysis. The posterior mar- 

 gin of one body and the anterior margin of the next poste- 

 rior body form the socket for the ventral head of the rib, the 

 parapophysis. As one progresses posteriorly through the 

 thoracic series, the neural spines slant more posteriorly and 

 become shorter. The pre- and postzygapophyses become re- 

 duced to facets. The prezygapophysis facet faces dorsally at 

 the anterior base of the spine, and that of the postzygapophysis 

 faces ventrally at the posterior base. The transverse process 

 becomes more and more anterior in position on the body 



142 • THE VERTEBRATE BODY SKELETON 



