140 
the Vertebrate classes, and also as showing its analogy in the Annu- 
lose animals. The table which he exhibited points out these, from 
which it would appear that Dr. Macdonald considers the bodies of 
the vertebrze,as described by anthropotomists,—continued downwards 
through the sacrum and coccyx to the top of the tail, and the basilar 
process upwards to the sella turcica,—as so many portions or segments 
of a central axis formed around a centrochord,—and not a notochord 
as usually described,—from which the autogenous elements spring 
and radiate to the periphery, and, converging mesially along the dorsal 
aspect, enclose within the tunnel of the Neuro-Camera the whole 
cerebro-spinal axis, of varying dimensions in the different regions, 
and another set of radii meeting sternally, and forming the three 
thoracic regions, having a costal region interposed. The Rachedian 
development from the sella turcica to the tail, with its mesothorax and 
metathorax, is the longest, and forms the Rachal type; the anterior 
towards the nose—the facial or proboscidian—is the shorter, and has 
only one thorax, the cephalothorax, formed by the mandibular cost 
and palatine sternum. 
«This framework, like a large trunk, is enclosed by three cycloid 
or segmental zones :— 
1. The Temporal, formed by the squamo-temporal, zygoma and 
malar bones, and supporting its membral or epicycloid ramus, formed 
by the maxilla. 
2. The Humeral or scapular clavicle and manubrium sterni, with 
its epicycloid ramus, the brachium, cubit and carpodactyle portions. 
3. The Cozal or ilio-pubic, with its epicycloid ramus, femur, crus 
and tarso-digital portions. 
«In so extensive a subject Dr. Macdonald restricted his present 
communication to the consideration of a portion of the epicycloid 
ramus of the metathoracic or coxal zone, and pointed out the strong 
analogy which might be traced between the tarsus and the bones of 
the arm in the human skeleton, in order to facilitate the examination 
of the same organs in the lower classes, and more especially in the 
osseous fishes, where, from an early prejudice, resulting from what 
appears to Dr. Macdonald as the hasty observation of preceding ob- 
servers, it has long been overlooked and considered as the homologue 
of the pectoral limb. This great error has rendered the whole sub- 
ject confused and complicated, and has given rise to many of what 
Dr. Macdonald considers the extravagances of Geoffroy St. Hilaire 
and his followers in the French school, and constrained them to mis- 
take the true respiratory or humeral epicycloid ramus, and superadd 
to this class the additional zone and membral ramus, under the vague 
idea of its being greatly developed tympanic bones; whereas, had 
they seen the analogy of the human tarsus and carpus, they never 
would have mistaken the tibia for the scapula or brachia, or the calcis 
for the ulna, and the scaphoid for the radius; and had they even 
examined the higher or cartilaginous fishes, they would have seen the 
opercular bones removed somewhat further down the trunk, and the 
pelvic or coxal zone and epicycloid ramus more distant. This would 
have led Professor Owen not to have considered the posterior extre- 
