472 Proceedings of the Poyal Society 
Monday , 29 th May 1871. 
Professor CHRISTISON, President, in the Chair. 
The following Communications were read 
1. On the Homologies of the Vertebral Skeleton in Osseous 
Fishes and in Man. By Professor Macdonald. 
Abstract. 
After a brief notice of the seven bi-vertebral segments of the 
cranium in man: — 
1. The liypo-cranial, or the axis and atlas vertebrae, which is 
adopted as a key to the cranial segments ; 
2. Para-cranial, or occipital; 
3. Wormi-epiotic parietal, or meta-cranial ; 
4. Sphenoidal, or meso-cranial ; 
5. Ethmo-frontal — pro-cranial ; 
6. Nasal, or apo-cranial. 
7. Rhino-nasal. 
Professor Macdonald gave a short outline of the osteology of the 
human cranium, in order to trace the homologous osteology of the 
osseous fishes, or ichthyia. 
The great characteristic of the vertebralia is the centro-chord, or 
axis, extending through the whole length of the animal from stem 
to stern, around or upon which the vertebral column has been 
developed This has been demonstrated in the very earliest type, 
both by the late Professor G-oodsir and Professor Owen in the 
Amphioxus, where the direction of the anterior portion, as far as 
the oral cleft, is to the tip of the nose from the anterior portion of 
the representative of the spinal marrow. The same proof may be 
adduced from the condition of the early human embryo, where 
the anterior of the embryo, consisting of the pro-cranium and part 
of the tubercles of the spine, are at once bent downwards, towards 
the upturned coccygeal extremity of the spine, where the umbilicus 
is afterwards formed, when the abdominal or ventral laminrn unite 
to close in the abdomen. There is another flexure of the pro-cranium 
and the meso-cranium in warm blooded vertebrata. 
