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 costae 

 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 stemi, with 

 its epicycloid ramus, the brachium, cubit and carpodactyle portions. 



3. The Coxal 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. 



