58 
Proceedings of the Royal Physical Society. 
be correctly assigned between the iclithyic 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 hsemapods, from having their feet and legs on the ventral 
or haemal 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 Antennae = VI. The Apocranio-Nasal. 
The Labrum = V. Frontal. 
The Mandible = IV. The Sphenoid Alse. 
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 lamellae and spines meet over the dorsal vessel or 
haeraaxis, 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 
