24 VERTEBRAL COLUMX. 



cannot be entirely omitted in a work on human anatomy. At the same time, it 

 is oln-ious that the complicated nature of the suliject, and the necessity for 

 frequent reference to details of comparative anatomy for its elucidation make it 

 impossible to enter fiiUy into its consideration here, so that our remarks must be 

 limited to those points in which the views of homolopry have the most immediate 

 bearing upon the knowledge of human anatomy. Tlie accomjianying views of 

 the several vertebras and some of their varieties from above (in fig. 21) may assist 

 the reader in comparing their forms. 



1. The series of centra or bodies, suiTounding the pi-imaiy axis of the noto- 

 chord, is complete in man. fi-om the jirocessus dentatus of the second vertebra to 

 the caudal extremity. In the head it is ascertained to be prolonged into the basi- 

 occipital and basisphenoid i^arts of the base of the skull. It is apjDarently absent 

 in the atlas, or rather the part coiTesponding to the centmm or body of that 

 vertebra is united with the body of the axis iii the odontoid process : while the 

 anterior arch of the atlas belongs to a different series of paits. not yet accu- 

 rately determined, perhaps to the precentral or subcentral parts or hi/pajwphyfic.-!. 

 The proofs of this view are derived mainly from. 1st. the remains of the noto- 

 chord having been actually traced in the foetus through the odontoid process 

 (and not through the anterior arch of the atlas) into the basioccijiital bone ; 

 2nd. the separate ossification in cartilage of the odontoid process : and Brd, the 

 existence in some animals, as the oniithorj-nchus and some reptiles, of a bone 

 coiTesponding to the odontoid process, in a separate condition, without any other 

 part representing the body of the atlas. 



2. The series of neural arches is complete in the whole vertebral column of 

 man. with the exception of the three lowest coccygeal vertebrce, and in jjart 

 of the upper coccygeal and lowest sacral vertebras. The neural spines are also 

 complete in nearly the same vertebras as the arches. The spme is absent or little 

 developed m the atlas, bifid at its extremity' in the next five cervical veilebrte. but 

 simple in all the remaining vertebras in which it is present. 



8. The articular processes, or zyg-apophyses, superior and inferior (ante- 

 rior and posterior iu animals). coiTesjiond m their relations throughout the whole of 

 the vertebras in which they exist, with the exception of both of those of the atlas 

 and the superior of the axis. In these last mentioned vertebras the articular ju-o- 

 cesscs are not in the series of zygapophyses. being situated at the place of union of 

 the pedicles with the bodies, or nearly in the place of the capitular articulation of 

 the ribs with the vertebral bodies, and therefore anterior to the jjlace of exit of 

 the spinal nerves, instead of jjosterior to it as in the other vertebras. In the 

 sacral vertebras the articular processes, existing as such in early life, come to be 

 m the adidt miited by anchylosis. In the three lower coccygeal vertebras they 

 are absent. 



4. It is in the comparison of the parts kno-mi in human anatomy under the 

 general name of transverse processes, that the main difiiculty of establishing 

 homologies exists. In all the cervical vertebras the processes so called are pierced 

 by a vertebrarterial foramen, and the most of them have two tubercles. Those of 

 the dorsal vertebrte are for the most part simple, but are articulated at two places 

 with the ribs. At these two places are situated processes, sometimes projecting in 

 animals to a considerable extent, which receive respectively the names of di- 

 nj>iij>hi/,siii a,nd jm ?-a J) np hi/. '<!.•>■ ; the first (diapophysis) being the tubercular or costo- 

 transverse, the posterior or upjjer articulation of the rib : the second, or par- 

 apophysis, being the capitular or costo-central articulation, the lower or anterior, 

 of the rib. placed close to the body but sejiarated from it by the neiu-o-central 

 sutm-e. It is very generally admitted that the part in front of the vertebrar- 

 terial foramen of the cervical vertebras con-esponds in series to the first part of a 

 rib ; as is illustrated by the separate ossification of that piece of bone in the 

 seventh cervical vertebra in man. and by the occasional occmTcnce of more fully 

 developed cervical ribs in that situation. 



The vascular passage in the dorsal region is between the neck of the rib 

 and the vertebra. In the lumbar vertebras the transverse processes are elongated 

 laterally, and at their root two other processes become apparent, viz., the mam- 

 millary or vwtcqfoplnjsis, looking upwards in man or forwards in animals, and the 



