58 Proceedings of the Royal Physical Society. 



be correctly assigned between the ichthyic and mammal 

 types. The first approach is made in the chondrous skelon 

 of the rays, where opercular bones are in relation to their 

 proper function, as the arm, supported on the scapulo clavi- 

 cular zone, having the hand greatly enlarged — in fact, 

 forming the large portion of the body of the skate — while 

 the pectoral fin is supported by the coxal or pelvic zone near 

 the commencement of the tail, as the claspers in the male. 



The crowding of the limbs about the cranium of fishes 

 has been pre-typified in the invertebral Annulo-zoa and 

 Arthro-zoa, which are neurapods, from having their legs and 

 feet so bent as to appear on the neural aspect ; the osteo-zoa 

 are haemapods, from having their feet and legs on the ventral 

 or haamal aspect. 



The insects and Crustacea, with their neural axis or 

 myelon below both the visceral and haemal axes, may be said 

 to walk on their back, and have all the thoracic rings closely 

 placed at the head, the oesophagus passing through the 

 neural ganglia representing the brain, in its way to the oral 

 opening, which, in all non-sessile animals, opens towards the 

 ground on which they walk. In both these classes the oral 

 apparatus consists principally of the early representatives of 

 the cranial metavertebral neur-arcs. 



The Antennas = VI. The Apocranio-NasaL 



The Labrum — V. Frontal. 



The Mandible = IV. The Sphenoid Alas. 



The Maxilla with its palpi — III. The Parietal. 



The Labium — II. The Wormi-otic. 



The Mentum = I. The Occipital. 



These represent the metavertebral neur-arcs. 



The invertebrate scleron has neither a central kaulon, nor 

 the metavertabral nor prevertebral pedicles ; but the pro- 

 vertebral lamellaa and spines meet over the dorsal vessel or 

 haemaxis, resting its tubercle on that of the metavertebral 

 lamellae, whose spines are united under the neuraxis. 



The prothoracic or temporal zone supports the prototype of 

 the vertebrate maxilla. 



The mesothoracic ring supports the arms, and represents 



