378 Zoological Society. 
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 costz 
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- 
mity or coxal zone and limb as the divergent appendages of the 
occipital vertebra. As to the homologies of these parts, the Doctor 
postponed the consideration of them till another opportunity, and 
proceeded simply with the tarsus. This consists in Man and many 
mammals of seven bones, which are arranged in two rows ; each row 
has developed from it one or more digital phalanges when most de- 
veloped ; with the first row the thumb or great toe is developed, while 
the other toes having metatarsal and digital phalanges are connected 
with the anterior row or distal end of the tarsus, where the tarsal bones 
are fused or developed in a single bone. ‘This is beautifully seen in 
many of the birds, especially the Cursores and Grallatores: in the 
Apteryx, as figured in the ‘Zoological Transactions’ by Prof. 
