546 CETACEA. 



centrum. In the seventh cervical vertebra, it would appear as if the process were 

 reversed and the head of the rib were merged in the tubercle. 



Erom these facts, regarding the development of the transverse processes of the 

 cervical region, it would appear that, as they occur in the atlas, axis, and third cervical 

 they are serially homologous with the superior transverse processes of the fourth, fifth, 

 sixth and seventh cervical vertebrae. The transverse process of the third vertebra is 

 occasionally, though rarely, perforated by a small foramen on one side, bat its position 

 is variable. Taking into account the foregoing observations relating to the develop- 

 ment of the processes before us, it is evident that this perforation is adventitious and 

 no guide to the ultimate nature of the process in question. It would appear also 

 that the whole area of the articular surfaces of the atlas and anterior facets of the 

 axis cannot be regarded as corresponding in position to the points of the attachments 

 of the heads of the ribs in the thoracic vertebrae, but only to that very limited 

 section which lies below the detached outer portion of the neurocentral suture ; 

 the superior aspect of those facets being apparently serially homologous with the 

 pedicles of the succeeding vertebral segments. 



In the thoracic region, in the younger foetus, the interval between the laminae 

 above the spinous processes is cartilaginous. The transverse processes of the first, 

 second, third, and fourth vertebrae are partially ossified at their bases, more especially so 

 in the first, but by far the greatest part of them is cartilage ; the succeeding transverse 

 processes of the thoracic vertebrae being wholly cartilaginous, as are also the 

 posterior zygapophyses. At the eighth vertebra, the pedicles become elevated from off 

 the side of the centra, till in the eleventh vertebra a wide interval intervenes between 

 the ossified base of the pedicle and the base of the transverse process. The first 

 indication of the metapophysis appears on the fifth dorsal. The heads and tubercles 

 of the ribs are only partially ossified. 



In the older skeleton, the first, second, and third laminae are not united, but all the 

 remaining ones are. The zygapophyses are entirely ossified. The neurocentral suture 

 is intact in all the vertebrae ; in the first four the transverse process is above 

 the suture, but in the fourth it occupies a much lower position than in the first, the 

 articular surface from the tubercle of the rib being brought close to the neurocentral 

 suture in all the dorsal vertebrae, the head of the rib being applied to the neuro- 

 central suture, so that with the downward removal of the transverse process there 

 is a corresponding confluence of the head and tubercle of the rib. In the fifth 

 vertebra, the transverse process is still lower, and its rib facet is distinctly prolonged 

 pn to the neurocentral suture. In the sixth, the confluent tubercle and head of the 

 rib is applied directly on the neurocentral suture, one-half to the inferior portion 

 of the pedicle, the remaining half over the neurocentral suture, and portion of the 

 body of the vertebra. In the seventh, eighth, and ninth, the articular surface from the 

 rib lies below the neurocentral sutures, being farthest removed from it in the ninth. 

 In the fifth vertebra, the transverse process is represented by a very slight expansion 

 of the outer extremity of the lamina and pedicle external to the metapophyses and 

 immediately above the neurocentral suture. In the sixth, it is still further reduced, 



