5-U CETACEA. 



able interspace between the dorsal extremities of the laminse. The transverse 

 process is situated between the upper extremities of the articular surfaces, external 

 to the base of the ossified neural arch. In a disarticulated skeleton, the vertebral 

 column of which is 19"50 inches in length, the atlas was found to be completely 

 ossified, but its constituent elements, the neural arch and hypapophysis, were not 

 united. The articulating surfaces are divided in their lower thirds by the suture 

 corresponding to the neurocentral suture of the other vertebrae, and which, when 

 the vertebra is in position with the axis, is seen to be continuous with the outer 

 margin of the odontoid. The laminae have almost united with each other. The 

 transverse process, which is ossified, is thus placed high above the neurocentral 

 suture, and corresponds to the superior processes of the cervical vertebrae as supposed 

 by Eschricht. It is continuous with the neural ossification, of which it is an 

 exogenous product. The lower arch is also fuUy ossified, and by the anterior 

 surface of its upper extremity it contributes to form the lower third of the anterior 

 articular surfaces of the atlas. 



In the axis of the foetus, the pedicles, posterior zygapophyses, and laminae are 

 ossified, but an interspace between the laminae above, and a considerable area external 

 to the centrum and involving the transverse process, are cartilaginous. The trans- 

 verse process is borne on the outside of the middle of the anterior articular surface 

 immediately below the inferior ossified extremity of the pedicle. In another specimen, 

 the process is seen to be entirely above the neurocentral suture and is imperforate, 

 so that Eschricht's view of the double nature of this process is not supported 

 by these facts. In the other foetus, there is no line of separation between the 

 centrum and the odontoid, but, in the anterior extremity of the latter, there is a well- 

 developed ossified mass. Anteriorly, the ossification of the neural arch is seen to be 

 spreading downwards into the anterior zygapophysis. The older specimen displays a 

 most instructive condition of the parts. The neural [arch, articular facets, and trans- 

 verse process are fully ossified, with the exception of the tip of the latter. The neuro- 

 central suture is intact, ciitting through the lower third of the anterior articular facets> 

 with the transverse process wholly above it and defining the outer limit of the odontoid. 

 This is fully ossified, but separated by a line of suture from the body of the axis ; 

 yet showing its double nature by a constriction in the middle of the posterior margin 

 of its lower surface, the halves of the centrum being still distinct and bulging 

 below to constitute the hypapophyses. 



In the third cervical, the inferior extremity of the ossified neural arch is separated 

 by a cartilaginous interval from the body of the vertebra ; this interval being con- 

 tinuous externally with a cartilaginous process investing the side of the centrum. 

 In the more matured specimen, a small foramen perforates the inferior extremity 

 of the base of the right transverse process ; but the neurocentral suture being intact, 

 the whole of the process is seen to lie above it. 



In the fourth cervical vertebra of the foetus, the lateral cartilaginous mass external 

 to the centrum is divided into two portions. The superior, lying below the neural 

 ossification, is broad and notched at its extremity, and is separated below by another 



