MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 329 



ossified, but commonly a communicating aperture is left between the two terminal 

 cones, and in many cases the plates by which calcification attains the periphery of the 

 body leave interspaces permanently occupied by cartilage, forming cavities in the dried 

 vertebrae, especially at their under part, or giving a reticulate surface to the sides of the 

 centrum. The expanded bases of the neur- and par-apophyses usually soon become 

 confluent with the bony centrum — sometimes first expanding so as wholly to enclose 

 it ; as, for example, in the Tunny, where the fine of demarcation may always be seen at 

 the border of the articular concavity, though it is quite obliterated at the centre, as a 

 section through that part demonstrates." Again, page 256 : — " In saurians, birds, and 

 mammals, the notochord is enclosed by cartilage before ossification begins, which car- 

 tilage is continuous with the cartilaginous neurapophyses. In birds, the two histological 

 processes, chondrification and ossification, do not precisely follow the same route. In 

 the centrums of the dorsal and cervical vertebrae of the Chick chondrification is centri- 

 petal : it begins from two points at the sides, and proceeds inwards, the middle line of 

 the under surface of the primitive notochord resisting the change longest. But, when the 

 lateral cartilages have here coalesced, ossification begins at the middle line and diverges 

 laterally ; the primitive nuclei of the bony centres appearing as bilobed ossicles, and 

 its direction is centrifugal. The lobes ascend to embrace the shrivelled remnant of the 

 chorda, like the hollow vei-tebral centres in fishes. Only in the sacral vertebrae has 

 ossification been seen to begin from two distinct points at the middle line. The bases 

 of the separately ossifying neurapophyses extend over much of the centrum, and soon 

 coalesce with it." Remark here, that the carotid canals are formed by exogenous mar- 

 ginal processes from the lower centre of ossification. We must be allowed to make 

 another quotation. Speaking, in page 260, of the development of the anterior vertebrae 

 of ' a large South American siluroid fish,' which has ' the first five centrums rigidly 

 fixed together by continuous ossification below,' although ' the concave articular cavities, 

 with the elastic capsules and contained fluid,' were seen in a vertical section, Professor 

 Owen says, "The continuous bony plate supporting those centrums was perforated 

 lengthwise by the aorta, offering another mode of the formation of a haemal canal — viz. 

 by exogenous ossification in and from the lower part of the outer layer of the capsule 

 of the notochord ; the carotid haemal canal in the necks of birds seems to be similarly 

 formed ; and the neck of the ichthyosaurus derives additional strength and fixation 

 from apparently detached developments of bone in the lower part of the capsule of the 

 notochord, at the inferior interspace between the occiput and atlas, and at those ot two 

 or three succeeding cervical vertebrae." 



Note. — The odontoid process of the mammalian axis is considered by our author to 

 belong to the same category'; but in that delightful little work of his on ' The Nature 

 of Limbs' (1849), this ossific centre is described as the main or internal part of the 

 centrum of the atlas, whilst the basal part of the atlas is considered to be the cortical 

 or hypapophysial portion of that bone. See pages 94, 107, and 112. 



' See page 2G1 of the same Report. 



